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Superheat vs Subcooling Explained

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Superheat vs Subcooling Explained

In this article, we’re breaking down a topic that every HVAC tech needs to understand—superheat versus subcooling explained. What are they? Why do they matter? And how do they help you diagnose a system?

Subcooling versus explained


Superheat

Superheat is the temperature of a vapor refrigerant above its boiling point at a given pressure. In other words, it tells us how much heat the refrigerant has absorbed after it has completely boiled into a vapor in the evaporator.


We measure superheat at the suction line, just before the refrigerant enters the compressor. This helps us confirm that only vapor—not liquid—is entering the compressor, which is critical for protecting it from damage.  


Here is an example, if the boiling point at a certain pressure is 40 degrees Fahrenheit (4.4 degrees Celsius), and the actual line temperature is 55 degrees Fahrenheit (12.8 degrees Celsius), then the superheat is 15 degrees Fahrenheit (8.3 degrees Celsius)

Superheat versus subcooling
Superheat versus Subcooling

Subcooling


Subcooling is the temperature of a liquid refrigerant below its condensing point at a given pressure. It tells us how much the refrigerant has been cooled after it has fully condensed into a liquid in the condenser.


Subcooling is measured at the liquid line, just before the metering device. Proper subcooling ensures that only liquid—not flash gas—is entering the TXV or cap tube.

Example:
If the saturation temperature is 100 degrees Fahrenheit (37.8 degrees Celsius) and the line temp is 90 degrees Fahrenheit (32.2 degrees Celsius), then your subcooling is 10 degrees Fahrenheit (5.6 degrees Celsius),


Here’s a quick side-by-side comparison:

  • Superheat is measured on the low-pressure side, after the evaporator
  • Subcooling is measured on the high-pressure side, after the condenser
  • Superheat protects the compressor
  • Subcooling protects the metering device
  • Both help ensure your system is charged properly


So why are these so important?


Too low superheat could mean liquid is getting to the compressor—bad news.
Too high superheat means the system is undercharged or the evaporator isn’t getting enough refrigerant. This indicates refrigerant vaporized too early, reducing cooling capacity and efficiency.


On the other side, too low subcooling can mean undercharging or flashing in the liquid line.
Too high subcooling might point to an overcharge or a restriction in the condenser.”


Superheating & Subcooling Target Temperatures

Superheat: 10 to 20 degrees Fahrenheit (5.6 to 11.1 degrees Celsius) depending on system and load

Subcooling: 8 to 15 degrees Fahrenheit (4.4 to 8.3 degrees Celsius) is common on most systems
But always refer to the manufacturer’s specs!”


And that’s the difference between superheat and subcooling! Two small measurements that make a huge difference in system performance.

If you found this article helpful, be sure to check out our HVAC and Plumbing Estimating Spreadsheets to streamline your construction bidding process, checkout our HVAC, Electrical and Plumbing Construction Forms to help you run your business and explore our Online Courses for in-depth training.

How to Calculate Bathroom Exhaust Air

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How to Calculate Bathroom Exhaust Air

How to Size Bathroom Exhaust

In this article, we’ll walk you through how to size commercial bathroom exhaust fans based on the 2024 Uniform Mechanical Code, the 2024 International Mechanical Code, and ASHRAE Standard 62.1.
We’ll take you step-by-step through real examples for a men’s and women’s public restroom.”

How to Size Bathroom Exhaust


Proper exhaust fan sizing in public restrooms isn’t just about odor control. It’s critical for indoor air quality, moisture removal, and meeting mechanical code compliance.
Undersized fans can cause lingering odors, humidity issues, and even damage building materials over time.


2024 UMC on Restroom Exhaust:

  • Light-use public toilet rooms require 50 CFM per water closet or urinal.
  • Heavy-use areas like stadiums or airports may require 70 CFM per water closet or urinal.

2024 IMC Exhaust Rates

  • 50 CFM per water closet or urinal if the fan operates continuously.
  • 70 CFM per fixture if the exhaust system runs intermittently.

ASHRAE Standard 62.1 supports similar rates but emphasizes overall airflow balance and indoor air quality targets.

Public Restroom Exhaust Air Rates per Fixture
Public Restroom Exhaust Air Rates per Fixture


Now let’s size the fans CFM for a real-world example.

Men’s Public Restroom:

  • 5 water closets
  • 5 urinals
  • Total: 10 fixtures

Women’s Public Restroom:

  • 5 water closets
  • Total: 5 fixtures
How to Calculate Bathroom Exhaust Air
How to Calculate Bathroom Exhaust Air

Step 1: Determine which code applies.

For our example we’ll use the IMC 2024 which using the terminology of continuous or intermittent operation. Determine if ventilation will be intermittent or continuous.

In this case, we’ll assume intermittent operation — the fans turn on with the lights or an occupancy sensor.

Step 2: Apply the exhaust rate.

Using IMC 2024 for intermittent operation of exhaust system for the restrooms gives us: 70 CFM per fixture.

Step 3: Calculate the total airflow:

For the men’s restroom:
10 fixtures times 70 CFM equals 700 CFM required

For the women’s restroom:
5 fixtures times 70 CFM equals 350 CFM required

Step 4 Determine Exhaust Makeup Air Method

Providing makeup air for exhausted air is essential to maintaining proper pressure balance. ASHRAE recommends ensuring air doesn’t flow from dirty areas into clean spaces and maintaining a negative pressure. This means providing enough make-up air from adjacent spaces or dedicated systems.

Common Exhaust Makeup Air Methods Include:

  1. Transfer Air: Air from adjacent spaces flows into the bathroom via door undercuts or grilles.
  2. Dedicated Conditioned Air: Supplied directly to the restroom through the HVAC system.
  3. Combination Method: A mix of transfer and limited conditioned air.

Step 5: Select exhaust fans.

Size fan or design ductwork to meet or exceed these total CFM requirements.

ASHRAE 62.1 - 2022 Table 6-2
ASHRAE 62.1 – 2022 Table 6-2


To summarize:

For private use restrooms the required exhaust is 25 CFM for continuous or 50 CFM for intermittent system operation.

Size exhaust fans based on fixture count and usage intensity.

UMC 2024, IMC 2024, and ASHRAE 62.1 work together to guide airflow requirements.

Always confirm whether the fans operate intermittently or continuously, and if using UMC, whether the public use is light or heavy to apply the correct rates.

Toxic Chemicals in Kids’ Mattresses: What Every Parent Should Know

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Toxic Chemicals in Kids’ Mattresses: What Every Parent Should Know

Toxic Chemicals in Kids Mattresses

Could your child’s mattress be affecting their health? A new scientific study just revealed something alarming about the air around children’s beds — and every parent needs to hear this. This channel is dedicated to good indoor air quality, so we thought this would be important for our readers and their friends and families to be aware of the toxic chemicals in kids mattresses.

Researchers from the University of Toronto, in collaboration with the Green Science Policy Institute, conducted a study measuring air quality in the bedrooms of 25 children aged 6 months to 4 years. They discovered elevated concentrations of harmful chemicals, including phthalates, flame retardants, and UV filters, particularly in the air surrounding children’s beds.

A companion study analyzed 16 commonly available children’s mattress brands and found that all contained concerning levels of these chemicals. Notably, one mattress was composed of 3% flame retardants by weight, and another exceeded Canada’s legal limit for a specific phthalate by more than double. Checkout safer options.

Health Risks Associated with Chemical Exposure

The chemicals identified in the study are linked to various health issues:​

  • Phthalates: Used to make plastics more flexible, these compounds are associated with hormonal disruptions, reproductive harm, and developmental issues.
  • Flame Retardants: Added to meet flammability standards, certain flame retardants have been connected to cancer, neurological damage, and lower IQ levels in children.​
  • UV Filters: Used to prevent fabric discoloration, some UV filters are suspected of causing hormonal disruptions and other health concerns.

Children are particularly vulnerable to these chemicals due to their developing bodies, higher respiration rates, and behaviors such as frequent hand-to-mouth activity

Recommendations for Parents

To minimize children’s exposure to these harmful chemicals, experts suggest the following measures:

How to Protect your Children from Toxins in Mattresses
How to Protect your Children from Toxins in Mattresses
  • Choose Safer Mattresses: Opt for mattresses made from natural materials like organic cotton or wool, which are less likely to contain harmful chemicals.​
  • Use Protective Barriers: Place a protective cover, such as a terry cloth towel, between the child and the mattress to reduce direct contact with potential toxins.​ Checkout safer options
  • Allow Off-Gassing: Air out new mattresses in a well-ventilated area for several days before use to allow volatile compounds to dissipate.​ Some chemicals take years to dissipate.
  • Regular Cleaning: Wash bedding and sleepwear frequently to remove any accumulated chemicals.​
  • Limit Bed Items: Reduce the number of items like pillows and stuffed animals on the bed, as they can absorb and re-emit chemicals.​
  • Air Purifiers: Use air purifiers to remove as much toxins as possible with a HEPA and Carbon filtration unit. Checkout the latest Air Purifiers.

While these steps can help reduce exposure, researchers emphasize that the ultimate responsibility lies with manufacturers to eliminate the use of toxic chemicals in children’s products. Get a Free Checklist below on what to look for to make a safe choice.

Calls for Regulatory Action

The study’s authors and health advocates are urging for stricter regulations to prevent the use of harmful chemicals in children’s mattresses. They highlight that many of these substances are not essential for meeting safety standards and pose unnecessary risks to children’s health

As awareness of indoor air quality issues grows, especially concerning children’s health, it’s crucial for both consumers and policymakers to advocate for safer manufacturing practices and more transparent product information.​

Free Toxic Chemicals in Kids Mattresses Checklist – Protect Your Child’s Health

Want to see which chemicals to avoid and what safer alternatives to look for? Download our free checklist below and subscribe for more updates on indoor air quality and family safety.

📥 Kids Mattress Toxic Chemicals Checklist (PDF)

HVAC Piping Labor Analysis

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HVAC Piping Labor Analysis

If you’re involved in HVAC piping—whether you’re an estimator, project manager, or contractor—there’s one critical skill that can make the difference between winning profitable jobs and constantly playing catch-up: labor analysis.

In fact, labor is often the largest and most unpredictable part of any mechanical piping estimate. And yet, it’s the area where most mistakes are made.

That’s why we created our online course: HVAC Piping Labor Analysis—a focused training designed to help you analyze labor accurately, avoid costly estimating errors, and take full control of your project’s financial outcomes.

Why Labor Analysis Matters

Materials are easy to price. Equipment comes with a quote. But labor? That’s where the real challenge begins.

Misjudging labor can lead to:

  • Underbidding jobs
  • Lost profit margins
  • Frustrated crews and delayed schedules
  • A reputation for missing the mark

HVAC Piping Labor Analysis gives you the tools and structure to prevent that. It’s not about guesswork—it’s about using real-world historical feedback data, industry knowledge, and practical estimating logic to create accurate and reliable labor projections.

What Impacts Labor in HVAC Piping?

Factors Affecting HVAC Piping Labor
Factors Affecting HVAC Piping Labor

Our full course dives deep into this, but here’s a high-level view of what you’ll need to understand (and what we train you to master):

  • Conditions Affecting Field Labor – Learn how jobsite access, working heights, climate, and project congestion impact crew productivity.
  • Pipe Rigging Methods – Explore how your choice of installation method can dramatically change labor hours.
  • Crew Size – Bigger isn’t always better. Understand how crew composition affects productivity rates.
  • Field Labor Productivity – Measure and apply realistic productivity factors instead of relying on generic charts.
  • Labor Analysis – Learn how to break down labor by system, area, and activity to pinpoint your true labor burden.
  • Estimating Review Meeting – Know how to present and defend your labor numbers in meetings with clarity and confidence.

These are the real-world estimating conversations that are happening every day. And if you’re not on point with your labor numbers, someone else will be.

The Missing Tool Most Estimators Wish They Had

What really sets this course apart? We’re not just teaching concepts—we’re giving you the tools to put them into action.

Every student gets access to our exclusive HVAC Piping Labor Productivity Calculator, a customizable Excel spreadsheet that helps you analyze, adjust, and calculate labor more accurately—every time.

Whether you’re building budgets, validating subcontractor quotes, or trying to tighten your bid margins, this tool saves time and increases confidence.

Take Control of Your Labor Estimates

If you’re serious about mastering HVAC piping labor estimation, don’t rely on guesswork, old habits, or outdated multipliers.

👉 Enroll in HVAC Piping Labor Analysis today and get the knowledge, system, and calculator you need to estimate smarter.

This course is ideal for:

HVAC Estimators
Project Managers
Mechanical Contractors
Engineers moving into estimating roles

Stop leaving money on the table. Start estimating labor with precision.

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