Essential Tools for Every Refrigeration Technician: A Comprehensive Review
Are you intrigued by the inner workings of refrigeration systems and the vital role they play in our everyday lives? Whether you’re an aspiring refrigeration technician or a seasoned pro, understanding the tools of the trade is essential.
In this comprehensive review, we delve into the top tools that every refrigeration mechanic should have in their arsenal. These tools are not mere conveniences; they are the very instruments that empower technicians to diagnose, repair, and maintain refrigeration systems efficiently and effectively.
1. Manifold Gauge Set: Refrigeration mechanics rely on manifold gauge sets to simultaneously measure high and low side pressures in refrigeration systems. These sets are like the eyes of the technician, providing critical insights into the system’s condition. By providing real-time data, refrigerant gauges are essential for diagnosing issues and ensuring optimal system performance.
2. Vacuum Pump: A vacuum pump may seem unassuming, but its role is monumental. It evacuates air and moisture from refrigeration systems before the introduction of refrigerant, ensuring that the system operates efficiently without unwanted contaminants.
3. Leak Detection Tools: Finding elusive refrigerant leaks is a challenge without the right tools. Leak detection tools, including electronic detectors and bubble solutions, play a crucial role in environmental protection and system efficiency by pinpointing these leaks.
4. Digital Multimeter: An HVACR technician’s electrical diagnostic prowess relies heavily on a digital multimeter. This tool measures voltage, current, and resistance in electrical components, making it indispensable for troubleshooting electrical issues.
5. Pipe Cutters and Flaring Tools: Copper pipes are the lifeblood of many refrigeration systems, and pipe cutters and flaring tools ensure these essential components are accurately cut and shaped for the job.
6. Pipe Benders: The importance of smooth, kink-free bends in copper pipes cannot be overstated. Pipe benders are the secret to achieving these precise bends without compromising the integrity of the pipe.
7. Thermometers and Thermocouples: When it comes to temperature measurement, accuracy is key. Thermometers and thermocouples help technicians monitor temperatures at various points in the system, assisting in both diagnostics and cooling optimization.
8. Tubing Tools: Properly preparing tubing for installation is a fundamental step in any refrigeration project. Tubing tools, such as deburrers and reamers, ensure that tubing is ready for action.
9. Hex Key Set: Hexagonal screws and bolts are commonplace in refrigeration systems. A set of hex keys is a technician’s trusty companion for swiftly disassembling and reassembling components.
10. Oil Pump and Oil Injector: Lubricating oil is the lifeblood of compressors. Oil pumps and injectors ensure that the compressor functions optimally by delivering the right amount of lubrication.
11. Torque Wrench: Precision matters in refrigeration systems. Torque wrenches guarantee that bolts and nuts are tightened to precise specifications, safeguarding components and maintaining proper seals.
12. Digital Scale: In the intricate world of refrigeration, precision is paramount. This is where a digital scale steps in as a silent but indispensable partner for refrigeration mechanics. Why? Because refrigerants, lubricants, and various chemicals must be added to systems with meticulous accuracy.
A digital scale ensures that the right quantities are added, helping maintain the system’s efficiency, performance, and, perhaps most importantly, the environment. It’s not just about getting the job done; it’s about getting it done right, and that’s where the digital scale shines. So, let’s weigh in on the importance of this often-overlooked tool in the refrigeration technician’s toolkit.
These tools are the cornerstone of any refrigeration technician’s toolkit. Stay tuned as we dive deeper into each of these essential instruments, unveiling the art and science behind their usage, and why they’re indispensable for refrigeration technicians around the globe.
In this article we’ll answer a question that we get all the time. What filter, if any, can filter out the SARS-CoV-2 virus which leads to COVID-19, the disease? We’ll show you how efficient the different air filters are at filtering out various items for asthma and allergy sufferers, and the virus that leads to COVID-19.
If you prefer to watch the Video of this presentation, then scroll to the bottom or click on the following link. Air Filters vs COVID-19
The ability of an air filter to remove microorganism, dust, pollen, dust mites, mold spores, pet dander, bacteria and viruses is indicated by a numerical value. This number, which is indicated as a MERV rating, states the filter’s efficiency at removing various sizes of these items. We’ll show you which filters, if any, work the best to protect you from these potentially harmful organisms.
Minimum Efficiency Reporting Values, or MERVs, indicate the filter’s ability to capture larger particles, those 0.3 microns and larger. The higher the numerical rating, the greater the air filter is at removing particles from the air stream. A MERV-13 is better than a MERV-11 filter at removing particles, but how good are they against bacteria and a very small virus that leads to COVID-19.
Virus and Bacteria Removal
According to ASHRAE, research has shown that the particle size of the SARS-CoV-2 virus that leads to COVID-19 is around 0.1 microns. This is much smaller than what may be picked up by these air filters. As this chart shows, the virus lives in the invisible region, while others like dust, cat dander and human hair are visible to the human eye.
Sizes of various items shown in Microns. Invisible items in black area on chart, including the SARS-CoV-2 Virus.
Luckily, the SARS-CoV-2 virus doesn’t travel through the air own its own. It rides on respiratory droplets and droplet nuclei (dried respiratory droplets) that are predominately 1 micron in size and larger. These filters have various efficiencies at capturing the viruses that are in the 1-to-3-micron range according to ASHRAE.
The SARS-CoV-2 virus riding a respiratory droplet in the 1 to 3 micron range
ASHRAE
As the chart shows, ASHRAE recommends using a minimum of a MERV 13 filter, which is at least 85% efficient at capturing particles in the 1 to 3-micron size range. A MERV 14 filter is at least 90% efficient at capturing those same particles. High-efficiency particulate air (HEPA) filters are even more efficient at filtering human-generated infectious aerosols.
MERV Rating and Air Filter Efficiency for Particle sizes 1 to 3 microns in size
By definition, a HEPA air filter must be at least 99.97% efficient at capturing particles 0.3 micron in size. This 0.3-micron particle approximates the most penetrating particle size (MPPS) through the filter. HEPA filters are even more efficient at capturing particles larger AND smaller than the MPPS. Thus, HEPA air filters are more than 99.97% efficient at capturing airborne viral particles associated with SARS-CoV-2 which leads to COVID-19.
HEPA filters can capture and trap microorganisms, including viruses and bacteria, helping to reduce the risk of respiratory infections. So, if possible, use the highest MERV rated air filter with your system, or get a portable HEPA air filter for your room or office. HEPA filters are the most efficient at capturing small microorganisms like the SARS-CoV-2 virus.
Where are HEPA Filters used?
HEPA air filters are used in residential, commercial, and industrial facilities. In homes there are portable types that can be moved from room to room, and others that can be installed in a central air conditioning system serving the whole house.
HEPA air filters are also used along with ULPA filters in cleanrooms, labs, and other spaces requiring a very clean environment.
Asthma and Allergy Management
For individuals with asthma, HEPA filters help reduce asthma triggers like airborne irritants and respiratory allergens. According to the Asthma and Allergy Foundation of America (AAFA), nearly 26 million people have asthma in the United States. There are 4.8 million children under the age of 18, and nearly 21 million adults suffering from asthma. On average, 10 people in the unites States die every day from asthma. A total of 3,517 deaths in 2021.
According to the AAFA over 100 million people each year in the United States experience various types of allergies. Allergies are the sixth leading cause of chronic illness in the U.S. HEPA filters are highly effective at removing allergens such as pollen, dust mites, and pet dander, providing relief to allergy sufferers.
Editorial Process:
Some of the links in this article may be affiliate links, which can provide compensation to the MEPAcademy at no cost to you if you decide to purchase. Our reviews and articles are made by an industry professional experienced in the engineering and construction of commercial buildings.
Are you paying too much for your HVAC equipment? How do you know if the quote you received for your equipment is a fair price? Do you have a method of comparing what you have paid for various HVAC equipment with what is being quoted currently?
Keeping track of the cost of HVAC Equipment allows you to quickly provide budgets and check the cost of equipment before you purchase. This database allows you to easily keep track of the most common HVAC equipment.
HVAC Equipment Cost Database
Using an HVAC Equipment cost database will save you a lot of money by avoiding the costly mistake of paying too much for equipment.
Air Conditioners in Historical Pricing HVAC Equipment Database
The HVAC Equipment Cost database keeps track of all your equipment quotes or purchases for easy reference and parametric checks, such as cost per ton ($/Ton), cost per CFM ($/CFM)
For an HVAC Piping Estimators the need for quick budgets for the installation of piping is best handled with a spreadsheet of different material types and sizes. Having an estimating software program can make this process a lot easier, as the material pricing is always up to date and can be entered into the spreadsheet quickly. You can get a copy of this spreadsheet to help you price piping fast and efficiently.
Often the requirements of the RFP or bidding instructions will call for the price per foot to install piping beyond that which is required by the contract drawings. Such pricing maybe used for change-orders. Having these numbers available and updated often also gives you a quick reference for budgeting projects. It’s good to know when doing job site comparisons of different piping options or during discussions with engineering, what the cost is for the various piping sizes and types of materials.
HVAC Piping Unit Pricing Calculator for Copper and Carbon Steel from 1/2″ to 14″
COST PER FOOT
The cost per foot for the installation of piping needs to include fittings and hangers prorated into the value. It’s best to look at a standard length of pipe and then figure that you will have a Tee and 90 degree elbow in that length.
So for example, using twenty feet of copper water pipe with a Tee and 90 degree elbow plus the hangers to build a unit price would represent a field condition of a fitting every ten feet.
For higher density projects like Hospitals you could put more fittings in your unit pricing. Total those cost up and then divide by 20 to derive at a cost per foot for that particular size and material type.
20 feet of pipe + 2 Fittings + 3 Hangers / 20 = Cost per Foot
If the piping is insulated, you can also put the values in for insulation.
The Estimating Wizard provides two spreadsheets for tracking unit pricing, one for HVAC Piping and the other for Plumbing piping. Get a copy and start tracking your cost per foot, or be prepared to give a quick budget based on your knowledge from your spreadsheet of unit prices. Watch the video below to see how quick and easy it is to track the cost per foot for various sizes and material types.
MEP Academy HVAC Piping Unit Pricing Spreadsheet
The MEP Academy provides a spreadsheet that makes calculating unit pricing simple. The spreadsheet is available by following this link, HVAC Piping Unit Pricing Spreadsheet
HVAC Piping Unit Pricing Calculator Example
In the screenshot above there is a place for you to build your hanger requirements (#1), and a place to put your tax rate and hourly labor rate (#2).
For each size of pipe and material type you would insert the unit cost for Material (#3) and Labor (#4).
Under item (#5) you would build your typical run of pipe and enter the quantity of fittings you might expect for the type of building and system. You would add whatever you think will be required for every so many feet of pipe. In the example above we are showing that for every 20 feet of pipe you will have 1 Elbow and 1 Reducing Tee.
Under item (#6) you would add the cost per lineal foot for insulation if required. You could also look at insulation as a separate value and leave the pipe bare.
Line item (#7) is where you indicate the hanger spacing, and for each hanger you defined under item (#1) you will get the quantity as defined by the linear feet in item (#5) divided by your hanger spacing, which will affect your cost.
Line item (#8) is the calculated cost per linear foot of piping for that size and material type of pipe.
Summary Sheet
After you have all your unit pricing information inputted into the spreadsheet, all you have to do to get a budget for installing piping is to enter the quantity of piping (#9) for each size and material type (#10). The system will automatically calculate the cost (#11) to install that run of piping based on your unit pricing data. The total cost will be shown at the top of the spreadsheet (#12).
The proper sizing and layout of condensate drain lines is important for the protection of property and for the proper functioning of the air conditioning equipment.
If you prefer to watch our YouTube version of this presentation, scroll to the bottom.
The size required for the condensate pipe is dictated by the local code. Enclosed you will find the requirements for many local codes, but be sure to check your code for your local requirements. If the outlet size of the equipment’s condensate drain is larger than what’s shown in this chart then your required to use the larger outlet size.
Minimum Condensate Drain Pipe Sizing Chart
Slope to be at least 1/8” per foot or 1 percent, that is for every 12” horizontally there must be at least an 1/8” drop vertically.
Condensate drain piping to slope a minimum of 1/8″ per every 12″ horizontal
Attics or Furred Spaces
If the Air Conditioner is suspended above an inaccessible ceiling, such as a gypsum board ceiling or attic space then you will need to provide a means for protecting the building elements from the overflow of the primary drain and for indicating that there is a leak.
Also, drain pans that are poorly drained can cause water to stay in the pan risking the possibility of algae and bacteria growth. Below are some possible solutions, but as always check your local code for the approved method.
Option 1 – Secondary drain pan with drain piping. This would hang below the Air Conditioning unit in case the A/C units primary pan overflowed. Also, there is a requirement to provide secondary drain piping to a point of termination that would provide notification to the occupants that there is a leak, such as terminating above a window or doorway.
Option 1 – Secondary drain pan with piping terminating in observable location
Option 2 – An additional drain pipe connection that sits above the primary drain connection and whereby the secondary drain piping terminates in a location to alert the occupants of the clogged primary drain.
Option 2 – Secondary drain piping connection to primary drain pan
Option 3 – Leak detection device that automatically shuts down the Air Conditioner if the primary drain becomes clogged.
Option 3 – Primary drain with leak detection device
Option 4 – Secondary drain pan with leak detection, located beneath the coil that shuts down the unit upon a leak.
Option 4 – Secondary drain pan with leak detection
The additional drain pan or drain pan connection shall be provided with a drain pipe that will determinate in an observable area, such as in front a window or above a doorway, and be of a size not less than 3/4”. Secondary drain pan shall not be less than 1-1/2” in height and extend 3” wider on each side of the coil or AC unit.
Secondary drain piping terminating above window. Pipe doesn’t have to be visible as shown.
Drain Termination
Where can and can’t you terminate the air conditioners condensate drain piping? There are several options where you can terminate the condensate drain line;
Indirect Drain
Condensate Pump to Indirect Drain
Drywell
Leach pits
Landscaped areas that are properly designed to handle the volume of condensate
To Properly designed stormwater treatment systems.
Indirect Drain
Lavatory tailpiece in the same tenant space as the air conditioner
Laundry standpipe
Janitors Sink
Inlet of Bathtub Overflow – Must be accessible
Collect and send to cooling tower (See description below)
Cooling Coil condensate to sink tailpiece.
The connection to a plumbing fixtures tailpiece has to be made within the same tenant space as the air conditioner cooling coil that is generating the condensate.
Drywell
A drywell can be used for the termination of your air conditioners condensate drain. Check your local code for the specifics, but generally it includes some or all of the following depending on whether it’s for residential or a commercial project:
A minimum size hole, such as 2 foot by 2 foot by 3 feet deep, or a round hole such as 12” diameter by 3 feet deep.
A minimum of 6” of soil or concrete shall provide cover above the rocks
Some form of barrier between the soil and the top of the drywell where the rock begins, such as building paper or plastic
Drywell to be filled with gravel or crushed rock, often with a stated minimum size rock such as 1 inch diameter
The termination of the condensate drain pipe shall connect indirectly to the drywell drain pipe.
The drywell drain pipe to be a minimum of 1-1/2” PVC or other approved material.
Drywell to be at least three feet away from the building structure or any footings.
Drywall for Air Conditioner Cooling Coil Condensate
There are various methods of providing drywells depending on the local code. There are prefabricated drywells that can be used and ones that are made by using a large diameter piece of PVC pipe or similar material.
Some codes will require you to collect the condensate from cooling coil drain pans and return it to the cooling tower if the equipment is served by a cooling tower and the total combined capacity of the HVAC cooling coils exceeds a certain amount like 65,000 btu/hr.
This is a water conservation measure, and there are some exceptions to this requirement, such as if the total capacity of the AC Equipment cooling coils are less than 10% of the total capacity of the cooling tower, or if the location of those AC Cooling coils are in a remote location, far from the tower.
Some locations where you can’t terminate condensate;
Public ways
Sidewalks
Driveways
Alleys
No termination of condensate on public area ways
Excluded from Code Requirements
Excluded from these codes are non-condensing type of equipment like radiant cooling panels that are designed to prevent condensate from occurring by keeping the temperature of the chilled water above the dew point temperature/vapor pressure of the surrounding air. These are system designed to operate in sensible cooling only modes.
Piping Material
The material types that can be used for condensate drain piping varies by jurisdiction but the most commonly cited materials are:
Copper
PVC – DWV
CPVC
ABS – DWV
Polyethylene
Galvanized steel
Cast iron.
Also the use of short radius 90-degree elbows are often prohibited. You can normally use standard fittings until you reach a certain size at which point you might be required to use drainage pattern fittings (DWV)
Traps
Traps are to be installed as required per the manufactures recommendation. No traps are required on the secondary drain pan, this is to allow immediate notification that the primary drain has failed.
Cleanouts
Cleanouts are required in case of plugged drain pipes. Provide as required to prevent the need to cut drain pipes for unplugging. Some of the following maybe used for cleanouts if approved by your local code authority;
Plugged tees
Union connections
Short clamped hoses at the unit (see image above)
When you have more than one air conditioning unit condensate tied to a main condensate pipe, then every change of direction shall have some method of cleanout. Check your local code as this maybe a requirement for even a single air conditioners condensate piping.
Condensate Pumps
Condensate pumps can be used to elevate the condensate vertically to a point where it will then discharge into a code approved gravity sloping condensate drain line. The condensate pump should be interlocked with the Air Conditioning Unit to prevent its operations if the condensate pump is inoperable.
Please remember that code requirements are always changing, so check for the most current code in your area at the time of design and installation. Or ask an inspector for the current installation practice.
Having an MEP Academy Estimating Spreadsheet that automates portions of your estimates, will save you valuable time that could be used to make more sales. All aspects of the cost of furnishing and installing an HVAC and/or a Plumbing system is contained in one spreadsheet made specifically for the MEP industry. For plumbing only see below.
For a Plumbing only Spreadsheet, use this Commercial & Residential Version. Plumbing Only. For a simple Residential HVAC & Plumbing Spreadsheet. Residential version.
The Main Dashboard provides you with all the information you need to make a quick decision on whether to make further adjustments, or if one of the metrics looks out of place based on historical data. The Dashboard gives you a quick overview of all that is going on within the Estimating Spreadsheet.
Estimating Dashboard within the MEP Academy Estimating Spreadsheet
Your MEP Academy Estimating Spreadsheet needs to be able to handle rental equipment, general conditions, subcontractors, piping and plumbing takeoffs, sheet metal, labor rate tables with crew mix capabilities, , and a bid summary. Each sheet in the estimating spreadsheet automatically calculates the values you enter, showing you a new total bid amount.
Will cover portions of the MEP AcademyEstimating Spreadsheet starting at the back of the Excel spreadsheet and working our way toward the front summary page last.
Choose your crew mix based on the level of experience and the different pay scales based on each project. Pick any combination and quantity of tradesman based on the requirements of the project.
Labor Rates and Crew Size within the MEP Academy Estimating Spreadsheet
There is a separate crew labor rate for HVAC Piping Shop & Field, Sheet Metal Shop & Field, and Plumbing.
Enter the project equipment price and labor to rig the HVAC and Plumbing equipment into place. Compare supplier pricing easily side by side. The MEP Academy Estimating Spreadsheet automatically selects the lowest bidder but lets you override that decision.
HVAC Equipment page within the Estimating SpreadsheetHVAC & Plumbing Equipment Sheets
Do you need a jobsite trailer or onsite management? Enter the quantity and level of the staff required to run the project, whether one person or dozens. Set the quantity and duration of each general condition, along with the rate. General Conditions is broken down into three sections as follows: #1 – Management, #2 – Construction Office (Non-Reoccurring Expenses), and #3 – Construction Office (Reoccurring Expenses).
HVAC & Plumbing contractors often subcontract out for Air & Water Balance, Sheet Metal & Piping Insulation, Water Treatment, Building Automation, Excavation and other specialty trades that they don’t self-perform. This spreadsheet was made especially for the HVAC & Plumbing contractor and their most often used subcontractors.
For those contractors that do plumbing the following Plumbing Fixture sheet will give you a place to record your vendors quotes and the labor it takes to install each type of fixture. What is also revealed is the overall cost per fixture.
Plumbing Fixtures page within the Estimating Spreadsheet
Each trade has a specialty sheet for those items that aren’t considered equipment or a fixture, but for which there is a cost impact. The MEP Academy Estimating Spreadsheet includes Sheet Metal, HVAC Piping & Plumbing Specialty sheets.
HVAC and Plumbing Specialty Pages within the Estimating SpreadsheetSpecialty Sheets in Estimate Spreadsheet
Material & Labor Summary Sheets
You will find a Sheet Metal, HVAC Piping & Plumbing material & labor summary sheets where all of the other specialty sheets are summarized for your review and last minute edits. Each sheet will be divided between field & shop fabrication work. The first section covers the field installation items.
Sheet Metal Material and Labor Summary – Estimating Spreadsheet
Each of the field labor summary sheets contain a row to add for the following
Material Handling
Consumables
Punch List
Cleanup
Detailing
Supervision
Shop Fabrication Summary Section
For those of you that have a fabrication shop, there is a section to add material and labor.
Shop Fabrication Summary
Rentals
For those HVAC air conditioning and Plumbing projects that require a crane, fork lift, scissor lift or any other equipment that you don’t own but will be required on the project. Having a spreadsheet that maintains a list of the most common equipment you normally rent along with their rental rate will save you time and money while avoiding having to call for pricing on every job.
Rental Sheet in Estimating Spreadsheet
Engineering
If you do your own design then you should have a sheet of each of the personnel responsible for spending time on the engineering task. If you’re doing design/build work, but don’t do the engineering yourself, but hire a third party, then you should add some engineering review time. It’s your responsibility to manage your third-party engineer to make sure they design within your cost parameters.
All of your estimates are summarized on the last tab of the MEP Academy Estimating Spreadsheet for easy review. You can quickly scan each of the categories to see where all the project cost has shown up. There is the labor and material summary for HVAC Sheet Metal, HVAC Piping, and Plumbing and another section for Subcontractors, General Conditions, Rentals, etc.
Estimating Spreadsheet Summary PageMEP Academy Estimating Spreadsheet Summary
The MEP Academy Estimating Spreadsheet contains a bid risk assessment form that rates the success of winning any particular project that you are contemplating pursuing. The risk assessment form will help you determine if the project is worth bidding based on a set of questions that rate your answers.
Bid Risk Assessment
The answers to these questions will give you a score from which you can use to see how the project rates on a scale of risk and reward. The total risk assessment score will also inform you which level of approval is required within your company depending on how you rate your risk values as the example shown below. The total score is 25, which according to this contractor would require the Vice President to sign-off on the project or approve the decision to pursue bidding on the project.
The MEP Academy Estimating Spreadsheet is used to gather all the information for estimating a project, putting it into a format where you can make quick adjustments and decisions while the spreadsheet gives you an immediate update on the price.
Purchase this spreadsheet at its currently reduced price of ONLY $245.00, which usually sells for $599.00
Watch the YouTube video below to see the MEP Academy Estimating Spreadsheet in action.
An HVAC VFD retrofit is one of the most common energy efficiency upgrades applied to existing fans and pumps in commercial buildings. When designed and commissioned correctly, a VFD retrofit can significantly reduce energy consumption at part-load conditions. However, many HVAC VFD retrofit projects underperform due to overlooked mechanical limits, poor controls integration, or incomplete commissioning.
However, in real projects, many VFD retrofits fail to deliver their expected savings—or introduce operational and comfort problems—because the system was never designed for variable-speed operation.
This article walks through the actual retrofit process, the engineering constraints, and the common pitfalls encountered when retrofitting fans, pumps, and motors with VFDs.
Flow or airflow is controlled mechanically (dampers or valves)
Energy is wasted during low-demand conditions
After the VFD retrofit:
Motor speed varies based on demand
Mechanical throttling is reduced or eliminated
Energy consumption drops significantly at partial load
The key takeaway: Energy savings come from reducing speed—not simply installing a drive.
2. When a VFD Retrofit Makes Sense
Not every fan or pump is a good candidate for a VFD retrofit.
Strong VFD candidates include:
Systems with variable demand
Long annual operating hours
Equipment that can tolerate turndown
Systems with a measurable control variable
Poor VFD candidates include:
Systems with strict minimum airflow requirements
Fans operating near surge or stall conditions
Equipment with no viable process variable
Systems with unresolved comfort or control issues
A VFD does not fix a poorly behaving system—it exposes it.
3. The HVAC Retrofit Process (Step-by-Step)
Step 1: Existing System Evaluation
Before any hardware is specified, the existing system must be understood.
Key questions:
What type of fan or pump is installed?
Is the motor original or a replacement?
Is the system belt-driven or direct-drive?
What safeties and interlocks exist today?
Field verification is critical. As-built drawings are often unreliable on older systems.
Here are two possible applications.
Pumps serving Two-way valve system
Remove the existing 3-way control valves and associated bypass piping, and replace them with 2-way modulating valves. This allows chilled water flow to vary with load instead of maintaining constant flow from the supply to the return.
Chilled water constant flow system with 3-way valves before retrofit.
Install a Variable Frequency Drive (VFD) to control the pump motor, first confirming that the motor is rated for VFD duty. If the motor is not VFD-rated, it must be replaced.
Next, install a differential pressure sensor to monitor system pressure as the control valves close. As differential pressure increases, the controller sends a signal to the VFD to reduce pump speed, lowering energy consumption.
Chilled water constant flow system with VFD and 2-way valves after retrofit.
Finally, verify that the chiller receives the minimum flow required for proper operation. Install a bypass line between the chilled water supply and return near the chiller, sized to maintain minimum evaporator flow when most valves are closed.
Garage Exhaust Systems.
Instead of operating the garage exhaust fan at full speed continuously, install a carbon monoxide (CO) monitoring and control system with multiple CO sensors throughout the garage. These sensors are connected to a Variable Frequency Drive (VFD), which modulates the exhaust fan speed to maintain carbon monoxide concentrations within safe limits.
Garage exhaust system with VFD controlling the fan based on CO levels.
When vehicle activity is low and carbon monoxide levels are minimal, the VFD reduces fan speed, significantly lowering energy consumption. As vehicle traffic increases and CO levels rise due to combustion engine operation, the controller automatically increases fan speed to provide the required ventilation and maintain code-compliant indoor air quality.
Step 2: Mechanical Constraints
Mechanical limitations are one of the most overlooked retrofit risks.
Key considerations:
Minimum airflow or flow requirements
Fan surge and pump cavitation limits
Bearing lubrication requirements at low speed
Resonance issues on belt-driven equipment
If the equipment cannot operate safely at reduced speeds, energy savings will be limited or nonexistent.
Step 3: Electrical Compatibility
Electrically, a VFD changes how the motor is powered.
Items that must be evaluated:
Motor insulation and VFD-duty rating
Distance between VFD and motor (reflected wave voltage)
Grounding and bonding
Harmonics and power quality impacts
Existing feeders and disconnect ratings
Many older motors survive VFD retrofits—but not all, and not without risk.
4. Controls: The Most Common Point of Failure
Most underperforming VFD retrofits fail due to controls, not hardware.
A VFD requires a process variable to modulate speed effectively.
Sizing electrical conductors for an air conditioner is a common task for HVAC professionals, electricians, estimators, and inspectors—but it is also one of the most misunderstood.
This article walks through how to properly size wire for an air conditioner using the National Electrical Code (NEC), explains why air-conditioning circuits follow different rules than standard branch circuits, and clears up common points of confusion related to ampacity tables, temperature ratings, and nameplate values.
Disclaimer: This article is for educational and informational purposes only. Electrical systems can be hazardous. Always comply with applicable electrical codes and regulations. Electrical work should be performed or reviewed by qualified or licensed professionals.
Air conditioners are not treated like general lighting or receptacle circuits under the NEC.
The compressor inside an air conditioner uses a hermetic motor, meaning the motor is sealed inside the compressor and cooled by refrigerant rather than open air. Because of these unique operating characteristics, air-conditioning and refrigeration equipment is governed by Article 440 of the National Electrical Code, not the general motor rules found elsewhere in the code.
This is why air-conditioning circuits often look “wrong” to people accustomed to standard wiring rules—but are fully code-compliant when evaluated correctly.
Always Start With the Equipment Nameplate
The most important rule when sizing conductors for an air conditioner is simple:
Always start with the equipment nameplate.
Every listed air-conditioning unit is required to have a visible nameplate that provides the electrical information needed for proper installation. Two values are critical:
Minimum Circuit Ampacity (MCA)
Maximum Circuit Breaker or Fuse Size
These values are determined by the manufacturer and already account for motor characteristics, starting current, and internal loads. When MCA and maximum breaker values are provided, you do not recalculate them—you verify and apply them.
Where the 125 Percent Rule Fits In
The NEC requires that branch-circuit conductors supplying air-conditioning equipment be sized at 125 percent of the rated load.
In modern equipment, this calculation has already been performed by the manufacturer. The result of that calculation is shown directly on the nameplate as the Minimum Circuit Ampacity (MCA).
In other words:
MCA already includes the 125 percent factor.
That is why you will not see us manually multiplying values by 125 percent when MCA is provided.
Most Air Conditioner Manufacturer include the 125 Percent in their MCA numbers.
Typical Residential Outdoor Condenser Wiring
For a typical residential outdoor HVAC condenser, the most common wiring method is:
THHN / THWN-2 copper conductors
Installed in PVC or metal conduit
Transitioning to liquidtight flexible conduit at the unit
These conductors are rated for wet locations, which is required outdoors. Although THHN/THWN-2 insulation is rated for higher temperatures, conductor ampacity is still governed by termination ratings, not insulation alone.
Why We Intentionally Use the 60°C Column
Even though many conductors have insulation rated for higher temperatures, ampacity must be based on the lowest temperature rating of any termination in the circuit, including:
Circuit breaker terminals
Disconnect lugs
Equipment terminals
Wiring method limitations
In many small HVAC branch circuits, these terminations are rated 60 degrees Celsius. Because of that, the safest and most universally applicable approach is to size conductors using the 60°C ampacity values from NEC Table 310.16.
This avoids assumptions, aligns with real-world inspections, and prevents misapplication of higher ampacity columns.
Simplified ampacity reference for educational purposes only. Always verify conductor sizing using the current NEC and applicable termination ratings.
Important Clarification: THHN / THWN and the 60°C Column
A common point of confusion is that THHN and THWN conductors do not appear under the 60°C column headingin NEC Table 310.16.
This does not mean they cannot be sized using 60°C ampacity values.
Manufacturers produce THHN and THWN conductors with 90°C insulation, which is why they appear under higher temperature headings. However, the NEC requires installers to limit conductor ampacity to the lowest-rated termination in the circuit.
That means installers can install 90°C-rated conductors and limit their ampacity to 60°C values when terminations require it—and this practice is completely normal and fully code-compliant.
Electrical wire sizing should consider the temperature rating of the weakest link including Breakers and Lugs.
This practice is standard in the field and expected by inspectors.
When a Higher Temperature Column May Be Used
If—and only if—all terminations in the circuit are clearly identified as rated 75°C, including:
Breaker terminals
Disconnect lugs
Equipment terminals
and the wiring method permits it, the NEC allows conductor sizing using the 75°C column.
This requires positive verification, not assumption.
In this article, we intentionally use the 60°C column because it is the most conservative and defensible approach, and it avoids relying on termination ratings that may not be clearly marked or verifiable in the field.
Worked Example Using the 60°C Column
Let’s walk through a real-world example using an actual air-conditioner nameplate.
Nameplate Information
Minimum Circuit Ampacity (MCA): 17.8 amps
Maximum Circuit Breaker: 30 amps
Step 1: Select the Conductor
Using NEC Table 310.16 and the 60°C copper column, we find:
#14 copper = 15 amps
#12 copper = 20 amps
Because the required MCA is 17.8 amps, #14 copper is not sufficient. The next standard conductor size is #12 copper, rated at 20 amps, which exceeds the MCA.
Result: ✔ #12 copper conductor is required.
Step 2: Verify the Circuit Breaker
The nameplate allows a maximum circuit breaker of 30 amps.
Under the special rules of Article 440, the Code permits this breaker size even though electricians typically associate #12 conductors with smaller breakers in general-purpose circuits.
As long as:
The conductor meets or exceeds the MCA, and
The breaker does not exceed the nameplate maximum
the installation is code-compliant.
Why the Breaker Can Be Larger Than the Wire
This is one of the most misunderstood aspects of air-conditioning circuits.
In these applications, installers do not size the breaker to protect the conductor from overload in the traditional sense. Instead, they size it to
Handle motor starting current
Provide short-circuit and ground-fault protection
Proper ampacity selection using MCA protects the conductor, while Article 440 permits the breaker to be larger.
The nameplate allows a maximum circuit breaker of 30 amps. Under the special rules of NEC 440.22, this section allows the breaker size to accommodate motor starting current, even though electricians typically associate #12 conductors with smaller breakers in general-purpose circuits. As required by NEC 440.6(A), the breaker does not exceed the manufacturer’s marked maximum.
Additional Considerations
Even after meeting MCA and breaker requirements, other factors may require upsizing conductors:
Ambient temperature derating
Voltage drop on long conductor runs (typically limited to 3 percent)
Bundling or conduit fill adjustments
These adjustments affect conductor size, not breaker size.
Final Compliance Summary for Sizing wire for an air conditioner.
For the example shown:
Required ampacity: 17.8 amps MCA
Selected conductor: #12 copper, 20 amps at 60°C
Circuit breaker: 30 amps, per nameplate
This installation meets NEC requirements for air-conditioning equipment.
Key Takeaways
Air conditioners follow NEC Article 440, not general wiring rules
Always start with the equipment nameplate
MCA already includes the 125 percent requirement
Termination temperature ratings limit conductor ampacity.
Using the 60°C column is often the safest and most defensible approach
Breakers may be larger than expected due to motor starting characteristics
Final Reminder for Sizing wire for an air conditioner.
Sizing wire for an air conditioner is not about memorizing formulas. It is about understanding which NEC rules apply, verifying nameplate information, and selecting conductors conservatively and correctly.
When in doubt, verify termination ratings, consult the current NEC, and involve qualified professionals.
Frequently Asked Questions
The following questions address common points of confusion about sizing electrical conductors for air-conditioning equipment. These answers clarify NEC requirements, nameplate values, ampacity tables, and real-world installation considerations to help you understand how HVAC circuits are evaluated and why the Code permits certain conductor and breaker combinations.
Common Questions About HVAC Wire Sizing
1) What size wire do I need for an air conditioner?
The unit’s nameplate Minimum Circuit Ampacity (MCA) determines the wire size. Choose a conductor with an ampacity equal to or greater than the MCA, using the correct NEC ampacity column based on termination temperature ratings.
2) What does MCA mean on an air conditioner nameplate?
MCA stands for Minimum Circuit Ampacity. The manufacturer provides MCA — the minimum conductor ampacity required for that unit’s branch circuit — in accordance with NEC air-conditioning rules.
3) Do I need to multiply by 125% when sizing wire for an air conditioner?
Usually, no. If the nameplate lists MCA, the manufacturer has already applied the 125% requirement. You size the conductor to meet or exceed the MCA.
4) Why can the breaker be larger than the wire for an air conditioner?
Air-conditioning circuits follow NEC Article 440, which allows installers to size the overcurrent device to handle motor starting current and provide short-circuit/ground-fault protection. As long as the conductor meets the MCA and the breaker does not exceed the nameplate maximum, it can be code-compliant.
5) Why does NEC Table 310.16 show #14 copper as 20 amps at 75°C?
#14 copper has an ampacity of 20 amps in the 75°C column, but you can only use that column if all terminations in the circuit are clearly rated 75°C and the wiring method allows it. Otherwise, you must use lower ampacity values.
6) If my terminals are rated 75°C, can I use the 75°C column to size the wire?
Yes—only if breaker terminals, disconnect lugs, and equipment terminals are all identified as 75°C rated, and the wiring method permits it. This requires positive verification, not assumption.
7) THHN/THWN doesn’t appear in the 60°C column—can I still use the 60°C ampacity values?
Yes. THHN/THWN-2 conductors typically have 90°C insulation ratings, but the lowest-rated termination in the circuit limits their ampacity. It is normal and code-compliant to use 60°C ampacity values when terminations require it.
8) What is the most common wire type used for a residential outdoor HVAC condenser?
Most residential outdoor condensers use THHN/THWN-2 copper conductors in conduit, transitioning to a liquidtight flexible whip near the equipment (depending on local practice and installation requirements).
9) Do I need to consider voltage drop when sizing HVAC wire?
Yes. For long runs, voltage drop may require installers to upsize conductors even if the MCA is met. A common design target is keeping branch-circuit voltage drop to around 3%.
10) Does ambient temperature affect the wire size for an air conditioner?
Yes. Higher ambient temperatures can reduce allowable ampacity and may require conductor upsizing. Always apply NEC adjustment factors when conditions warrant.
11) Should I rely on the nameplate or the breaker size to choose wire?
Use the nameplate MCA to choose the wire size and the nameplate maximum breaker to choose the overcurrent device. The breaker size alone is not a reliable way to select wire for HVAC equipment.
12) Is it safe for homeowners to work on air conditioner electrical wiring?
Electrical work can be hazardous. Qualified or licensed professionals should perform or review it in accordance with applicable codes and regulations.
How do engineers, facility managers, and property owners fairly compare energy use between different buildings? The answer lies in ENERGY STAR’s Portfolio Manager, a free benchmarking tool developed by the U.S. Environmental Protection Agency (EPA). While most people recognize the ENERGY STAR label from household appliances—such as refrigerators, washers, dryers, water heaters, and air conditioners—many are unaware that ENERGY STAR also evaluates and rates entire buildings using standardized performance metrics. Two of the most important of these metrics are Energy Use Intensity (EUI) and the ENERGY STAR 1–100 building score.
Portfolio Manager provides a consistent, nationwide framework for measuring, comparing, and tracking building energy performance over time, allowing similar buildings to be evaluated on an equal basis.
One of the primary metrics used to compare buildings is Energy Use Intensity (EUI). EUI is calculated by dividing a building’s total annual energy consumption by its gross floor area:
EUI = Total Annual Energy Use ÷ Building Square Footage
The result is expressed in kBtu per square foot per year, and it allows for quick, normalized comparisons between buildings of different sizes. A lower EUI generally indicates a more energy-efficient building.
EUI Comparison Example
Consider an example where two buildings—an office building and a hospital—each consume 8 million kBtu per year:
The office building is 50,000 square feet, resulting in an EUI of 160
The hospital is 17,000 square feet, resulting in an EUI of approximately 470
Although both buildings consume the same total amount of energy annually, the hospital uses nearly three times more energy per square foot. EUI reveals this difference clearly, whereas total energy use alone does not.
Table 1 — Energy Use Intensity (EUI) Comparison Example
Purpose: Visually demonstrates why EUI matters more than total energy use alone.
Building Type
Annual Energy Use (kBtu)
Building Size (ft²)
EUI (kBtu/ft²·yr)
Office Building
8,000,000
50,000
160
Hospital
8,000,000
17,000
470
Key Insight: Even with identical annual energy consumption, the hospital uses nearly 3× more energy per square foot, making it significantly more energy intensive.
The Golf Score Analogy
EUI can be compared to a golf score. In golf, the objective is to achieve the lowest score possible. Similarly, with Energy Use Intensity, a lower EUI represents better energy performance. Just as golf scores allow players to compare performance regardless of course length, EUI allows buildings to be compared fairly regardless of size.
Site Energy vs. Source Energy (Why the Difference Matters)
When benchmarking buildings, it is important to distinguish between site energy and source energy, as the two represent very different views of energy use.
Site energy is the amount of energy consumed directly at the building and is what appears on utility bills. It includes electricity used at the meter, natural gas burned on site, fuel oil, and district energy delivered to the building. While site energy is useful for tracking operating costs, it does not account for how that energy was produced or delivered.
Source energy, on the other hand, represents the total amount of raw fuel required to operate the building. It includes the energy consumed at the building plus all upstream losses associated with electricity generation, fuel processing, and transmission and distribution. Because electricity requires significant energy losses before it reaches a building, source energy provides a more complete and equitable picture of total energy impact.
ENERGY STAR uses source energy and source EUI for national benchmarking because it places all energy sources—electricity, natural gas, district steam, and others—on a common basis. This prevents buildings from appearing artificially efficient or inefficient simply due to regional utility infrastructure or fuel mix differences.
Table 2 — Site Energy vs. Source Energy Comparison
Purpose: Clarifies why ENERGY STAR prefers Source Energy for benchmarking.
Category
Site Energy
Source Energy
Measured At
Building utility meter
Power plant + transmission + building
Includes Generation Losses
❌ No
✅ Yes
Includes Transmission Losses
❌ No
✅ Yes
Fuel Comparability
Limited
Fully normalized
Used for ENERGY STAR Score
❌ No
✅ Yes
Best For
Utility cost tracking
National benchmarking
Key Takeaway: Site energy tells you what you paid for. Source energy tells you what it really took to produce it.
Benchmarking Similar Building Types
Meaningful benchmarking requires comparing similar building types. Just as it would be inappropriate to compare a professional golfer to a 10-year-old, it would be misleading to compare an office building to a hospital or data center. Instead, ENERGY STAR Portfolio Manager compares buildings within the same category—offices to offices, hospitals to hospitals—using a large national database.
Engineers assist property owners by benchmarking buildings against:
Other buildings within their portfolio
The national median for similar building types
Peer buildings nationwide within Portfolio Manager
This process helps identify underperforming buildings and target energy efficiency improvements where they will have the greatest impact.
Table 3 — Typical Median Source EUI Benchmarks (U.S.)
Purpose: Provides context for what “good” or “poor” performance looks like nationally.
Building Type
Median Source EUI (kBtu/ft²·yr)
Warehouse (Non-Refrigerated)
~80
Multifamily Housing
~124
K–12 School
~153
Office (All Sizes)
~167
Retail (Non-Refrigerated)
~160
Hotel
~208
Medical Office
~237
Hospital
~426
Grocery Store / Supermarket
~500–600
Data Center
600+
Interpretation Guide:
Below median → Better than at least 50% of similar buildings
Above median → Opportunity for efficiency improvements
ENERGY STAR 1–100 Building Score
For eligible commercial and institutional buildings—including offices, schools, hospitals, retail stores, and multifamily housing—ENERGY STAR provides a 1–100 ENERGY STAR score through Portfolio Manager.
Key points:
A score of 50 represents median (average) performance
A score of 75 or higher indicates top-tier performance, better than at least 75% of similar buildings nationwide
Buildings scoring 75+ may qualify for ENERGY STAR certification
Certification is awarded annually, requires verification by a licensed professional (such as an engineer or architect), and formally recognizes superior energy efficiency. Advanced programs, such as ENERGY STAR NextGen, further recognize buildings with exceptionally low emissions.
Thousands of buildings across the United States have earned ENERGY STAR certification, and owners can benchmark their own buildings or search certified properties at energystar.gov/buildings.
ENERGY STAR Score vs. Energy Use Intensity (EUI)
The ENERGY STAR score and EUI are closely related metrics within Portfolio Manager, but they serve different purposes.
Key Similarities
Both normalize energy use by building size (kBtu/ft²·yr)
Both rely on national survey data, primarily the Commercial Buildings Energy Consumption Survey (CBECS)
The ENERGY STAR score is derived from source EUI, which accounts for upstream energy losses in fuel production and delivery
Differences and Relationship
EUI (site or source) is an absolute metric: total annual energy use divided by floor area. While lower EUI typically indicates better performance, raw EUI alone does not adjust for differences in climate, occupancy, or operating hours.
The ENERGY STAR score compares a building’s actual source EUI to a predicted source EUI, calculated using regression models that account for weather, occupancy, operating hours, and building characteristics.
A ratio of actual-to-predicted energy use near 1.0 results in a score of approximately 50
In short, EUI is the foundational intensity metric, while the ENERGY STAR score is a normalized, percentile-based benchmark built on EUI for fair peer comparisons. For building types that are not eligible for a 1–100 score, Portfolio Manager typically defaults to displaying EUI as the primary performance indicator.
Table 4 — EUI vs. ENERGY STAR Score
Purpose: Explains the relationship and differences between the two metrics.
Feature
EUI
ENERGY STAR Score
Metric Type
Absolute
Relative (Percentile)
Units
kBtu/ft²·yr
1–100
Normalized for Size
✅ Yes
✅ Yes
Normalized for Weather
Optional
✅ Yes
Adjusted for Operations
❌ No
✅ Yes
Peer Comparison
Manual
Automatic
Certification Eligible
❌ No
✅ Yes (≥75)
ENERGY STAR vs. LEED
ENERGY STAR for buildings focuses primarily on operational energy efficiency, providing performance-based benchmarking and certification. Portfolio Manager also supports tracking of water use, waste, materials, and greenhouse gas emissions.
In contrast, LEED is a broader green building rating system that evaluates energy performance alongside water efficiency, materials, indoor environmental quality, site impacts, and innovation through a point-based framework.
The two systems are highly complementary. Strong ENERGY STAR performance often contributes directly toward LEED credits, particularly in energy and performance-related categories.
Comparing Current Performance to Historical Energy Use
Engineers also use historical energy use data to analyze trends over time. By comparing year-over-year energy consumption and EUI values, they can identify patterns such as seasonal peaks, long-term increases, or improvements resulting from equipment upgrades, operational changes, or retrofits.
This historical analysis helps distinguish between weather-driven variability and true efficiency gains, supports capital planning decisions, and provides measurable evidence of performance improvements. When combined with benchmarking against national medians and peer buildings, historical energy analysis becomes a powerful tool for managing energy costs, reducing emissions, and improving overall building performance.
How to size tankless water heaters correctly is all about math and realistic assumptions, not guesswork. If you undersize the unit, showers go lukewarm or the flow drops to a trickle when multiple fixtures run. Oversize it, and you may pay more for equipment and infrastructure than you need.
This guide walks through the process step by step so you can confidently determine what size tankless unit you actually need (and then confirm it with manufacturer tools and a professional).
A tankless water heater is sized by how much hot water it can produce at a given temperature rise, not by storage gallons.
Three key concepts:
Flow rate (GPM – gallons per minute) How many gallons of hot water your fixtures demand at the same time.
Temperature rise (ΔT) How many degrees you need to heat the incoming (groundwater) water to reach your desired hot water temperature.ΔT=Tout−TinΔT=Tout−Tin
Heater capacity (BTU/h or kW) The gas input (for gas units) or electrical power (for electric units) required to deliver that flow and temperature rise.
Manufacturers publish charts or calculators that tell you, for example, “this model can deliver 5.0 GPM at a 70°F temperature rise.”Rheem+1
Your job is to calculate:
Required GPM at peak use + Required temperature rise → Select a model that meets or exceeds both.
Step 1 – Define the Application
Before any math, be clear about what you’re sizing for:
Whole-house tankless (most common)
All showers, sinks, laundry, etc.
Point-of-use (single fixture or small group)
Example: one bathroom group, or a remote studio sink/shower.
Residential vs. small commercial
Commercial may have different diversity and fixture types.
Also consider:
Number of bathrooms
Typical household size (people)
Any high-demand fixtures: large soaking tub, body spray shower, commercial dishwasher, etc.
This will drive what “peak simultaneous use” actually looks like.
Step 2 – List Your Hot-Water Fixtures and Their Flow Rates
Next, list all fixtures that use hot water, plus their typical flow rates. You can find exact flow on product spec sheets or measure with a bucket, but here are common ranges from tankless sizing resources:PlumbingSupply.com+1
Typical residential flow rates
Standard shower: 1.5–2.5 GPM
Water-saving shower: 1.2–1.8 GPM
Bathroom sink faucet: 0.5–1.5 GPM
Kitchen faucet: 1.5–2.2 GPM
Clothes washer: 1.5–3.0 GPM
Dishwasher: 1.0–2.0 GPM
Large tub filler: 4.0–6.0+ GPM
Body spray/“carwash” shower systems: often 4.0–8.0+ GPM total
Create a simple table like this for your project:
Fixture
Flow (GPM)
Notes
Shower #1
2.0
Primary bathroom
Shower #2
2.0
Hall bath
Bathroom sink (same bathroom)
0.7
Brushed nickel low-flow faucet
Kitchen sink
2.0
High-arc faucet
Dishwasher
1.5
Spec sheet list
Clothes washer
2.0
Top-load
Step 3 – Decide What Really Runs at the Same Time
You don’t size for every fixture running at once. You size for a realistic peak scenario.
Examples of reasonable peak scenarios:
Family home (3–4 people)
Two showers running + one bathroom sink intermittently
Small home / couple
One shower + kitchen sink or dishwasher
Home with large soaking tub
Either tub filling or one shower + one sink (not both scenarios at once unless that’s realistic for that client)
For each project, write down one or two “design scenarios” you actually want the system to support.
Example design scenario
Two showers running at the same time, plus a bathroom sink occasionally.
From the table above:
Shower #1: 2.0 GPM
Shower #2: 2.0 GPM
Bathroom sink: 0.7 GPM
Total design flow = 2.0 + 2.0 + 0.7 = 4.7 GPM (Round to 4.5–5.0 GPM for simplicity.)
Step 4 – Determine Incoming Water Temperature and Temperature Rise
Now estimate your incoming (groundwater) temperature. This varies by climate. Many sizing tools and guides use groundwater temperature maps and typical desired hot water temperature around 120°F.energy.gov+1
You can:
Look up your region on a groundwater temperature map from a sizing tool.
Use local data (well temp, etc.) if you have it.
Use conservative values for winter conditions (coldest likely incoming temp).
Typical incoming temps:
Cold northern climates: 35–50°F
Mixed / temperate: 50–60°F
Warm southern climates: 60–75°F
Most households are happy with 115–120°F at fixtures, even if the water heater is set slightly higher.
Example
Incoming water: 50°F (cool climate)
Desired outlet temp: 120°F
ΔT=120°F−50°F=70°FΔT=120°F−50°F=70°F
So this home needs about a 70°F temperature rise at their design flow rate.
Most residential gas tankless units are in the 150,000–199,000 BTU/h range, so in this example you’d likely be looking at the larger end of that range to comfortably meet 4.5–5.0 GPM at a 70°F rise.
Rule of thumb: For typical homes in cool climates, whole-house gas tankless systems often land in the 180k–199k BTU/h range. Electric whole-house tankless units may require very large electrical service to match this performance.
Step 6 – Match Your Numbers to Manufacturer Sizing Charts
Now that you know GPM and ΔT, you compare that to manufacturer data.
PDF charts and spec sheets showing max flow at different temperature rises.Gateway ACPro+1
Look for a table or chart that says something like:
70°F rise → 4.5 GPM
60°F rise → 5.5 GPM
50°F rise → 7.0 GPM
Then compare your requirement:
Need ≥ 4.5 GPM at 70°F rise
Pick a model that meets or exceeds this capacity.
If a model only provides 3.5 GPM at a 70°F rise, it’s too small for our example home. Either:
Move up to a larger model, or
Decide that your realistic design scenario is less demanding (e.g., only one shower + a small sink at once).
Step 7 – Check Fuel Type and Site Constraints
Even if the math says a certain size will work, your building infrastructure has to support it.
Gas tankless units
Check:
Gas line size and pressure – High-input gas models (e.g., 180k–199k BTU/h) often require upgraded gas piping and proper inlet pressure.
Venting – Condensing models may allow PVC/CPVC/polypropylene venting and have higher efficiency; non-condensing may need metal venting.Navien+1
Combustion air – Especially for indoor installations.
Condensate drain – Required for condensing units; you need a place to route neutralized condensate.
Electric tankless units
Check:
Available service amperage and voltage – Whole-house electric tankless units may require multiple 40–60A double-pole breakers and heavy conductors.Stiebel Eltron USA+2Stiebel Eltron USA+2
Panel capacity – Many homes don’t have enough spare capacity without a service upgrade.
Local code requirements for electric water heaters.
If the site can’t support a large enough unit, you may need:
Multiple smaller point-of-use units, or
A high-efficiency tank or heat pump water heater instead of whole-house tankless.
Step 8 – Decide Between One Large Unit or Multiple Units
If one heater can’t cover everything (or would be very expensive to support with gas/electric infrastructure), consider multiple units:
Two smaller tankless units in parallel (“ganged”) to share load. Many manufacturers specifically allow this, and some calculators will flag when ganging is recommended.PlumbingSupply.com+1
Separate zones:
One unit for “main house” (showers, laundry)
One smaller unit for “kitchen/guest wing” or remote structures
This can also offer redundancy and shorter hot-water runs (less wait time, less wasted water).
Step 9 – Adjust for Special Fixtures and Recirculation
High-demand fixtures
If the home includes:
Large soaking tub,
Multi-head shower or body sprays,
Commercial-style kitchen equipment, or
Multiple simultaneous uses in a big family,
You must account for those extra GPM in your design scenario, or accept that they can’t all run at once.
Often this pushes designers toward:
Two tankless units, or
Hybrid solutions (tankless feeding a small buffer tank, etc., in some designs).
Recirculation systems
Tankless units with recirculation:
Don’t change the peak GPM the heater must produce,
But they do impact control strategy, pump sizing, and standby losses.
Many manufacturers offer built-in recirc pumps or recirc-ready models, with specific piping diagrams and control options that should be followed.Navien+1
Step 10 – Confirm Everything with Manufacturer Tools and a Pro
Once you’ve worked through the sizing yourself, sanity-check your decision using:
Important fine print: many of these tools explicitly state that they’re guides only, and that the contractor or engineer is responsible for the final selection and ensuring code compliance.naviensizing.com+2Gateway ACPro+2
Work with a qualified installer or engineer to:
Verify your load calculations
Confirm gas/electric capacity and venting
Ensure code compliance and proper safety/clearance provisions
Common Sizing Mistakes to Avoid
1. Using number of bathrooms only Bathroom count is a rough screening tool, but real sizing needs actual fixture flow and realistic concurrency.
2. Ignoring cold-climate conditions If you size using average or summer groundwater temperatures, you may be under-sized in winter.
3. Not checking gas or electric infrastructure Discovering after purchase that your gas line or electrical panel is too small is an expensive surprise.
4. Forgetting about special fixtures Body sprays, big tubs, and commercial appliances are GPM hogs—don’t ignore them.
5. Assuming any “199k BTU” unit is automatically enough Different models can have different actual delivered GPM at your ΔT. Always check the flow vs. temperature rise table.
Quick Sizing Checklist
Use this as your “don’t guess” checklist:
List all hot-water fixtures and their flow rates (use spec sheets or typical values).
Define a realistic peak use scenario (what’s actually on at once).
Add up GPM for that scenario.
Determine incoming groundwater temperature and desired outlet temperature; compute ΔT.
Use BTU/h ≈ 500 × GPM × ΔT to estimate needed capacity.
Compare your GPM & ΔT to manufacturer flow-vs-rise charts or calculators.
Verify gas line, venting, and electrical capacity can support the chosen unit.
Decide whether you need one whole-house unit or multiple / point-of-use units.
Factor in high-demand fixtures and recirculation if present.
Confirm selection with manufacturer tools and a qualified installer.
Follow that process and you’ll be sizing tankless systems deliberately, not guessing.
