The fan blows or sucks air through a duct and exits or enters a piece of air distribution. There are different types of air distribution devices based on types of ceilings and the engineer’s preference. In the image below there are three different ceiling types (1, 2, 3) shown for the Supply Air Diffusers.
Ceiling Types
#1 – No ceiling (There is no ceiling in this room because it’s used for the engineering dept.)
#2 – Gypsum board ceiling.
#3 – Acoustical tile (2’ x 4’)
Ceiling Types for Air Distribution
Remember that the Architectural Reflected Ceiling Plan shows the type of ceiling for each area. The Mechanical engineer may use that reflected ceiling plan has the starting background image before they design the HVAC system over it.
Supply air grilles and registers have options on the directional throw as shown in the image above, you have Supply Ceiling Diffuser (#1) shown as a 3-way throw, hence the three arrows. Supply Ceiling Diffuser (#2) is shown as a 2-way throw, and Supply Ceiling Diffuser (#3) is shown as a 4-way throw.
Have you ever been in a restaurant or other place of business and felt a draft drop down over you while you were sitting eating or conducting business? This is poor air distribution design, as you should never feel the air, it should just blend in without any draft on you.
Linear Diffusers
Linear diffusers are used in areas that require a more aesthetically pleasing look due to the ceiling design or layout.
The plenum will be installed first and then once the sheet rock is installed, the sheet metal field technician will return to install the actual linear diffuser.
Linear Slot Diffusers
Shown below is what a linear supply and return diffusers looks like on the actual drawings. Each engineer draws them slightly different, but it should show as a skinny long grille. The blue arrows show the supply linears and the orange arrow shows the return linear.
In this design, the return air is ducted as shown by the single line duct leading from the center of the back of the linear. Often in commercial buildings the return air will be non-ducted, in which case the air will travel back to the HVAC equipment through the attic space.
Linear Diffusers as Represented on Drawings
HEPA and ULTRA HEPA Filter Grilles
HEPA filters are used when cleanliness is a requirement for a space. This could be a pharmaceutical or micro-chip manufacturer, hospital or laboratory. There are various levels of cleanliness from ISO-1 through ISO-9, or Class 1 through Class 100,000. You don’t have to worry about this right now, but you will need to get pricing and provide labor to install. Watch the video below to see what a 2’ x 2’ HEPA filter grille looks like.
HEPA Filter
Fan Powered HEPA Filters
This is a special type of air distribution device where a fan is located within the housing that supply’s air through a HEPA filter to provide clean air to a critical space such as a cleanroom or operating room. You would request a quote from the manufactures representative and provide the appropriate labor to install them. It takes much longer to install these special air distribution devices than a normal diffuser, possibly 2 to 4 hours each depending on the type and hanging requirements.
Fan Powered HEPA Filtration
Flexible Duct Connections
The majority of air distribution connections from branch ducts are made with a flexible duct connector. This is represented by a little squiggly mark between the duct and the air distribution diffuser.
Flexible Duct Connection
Some air distribution diffusers won’t need a flexible connector as they maybe located where there isn’t a ceiling as shown in the below image. In this case you would use a hard 90-degree elbow. In some jurisdictions, the use of a 90-degree elbow is mandated by code, so check your local code authority.
No Flex
The following shows the proper method of attaching flexible duct to either the can or collar on the Air Distribution Diffuser or the branch duct.
Item #1 shown in the image below shows that a bead or lances provide the best method for keeping the flex secured in place. If the flex will be hanging vertically with gravity and its own weight pulling down, then its recommended to add sheet metal screws (#2) to hold it from slipping off.
Flex Duct Assembly
Estimating Spreadsheet
Enter the information on your estimating spreadsheet under the HVAC Equipment Tab. Indicate the Quantity of each type (#2), the Total Quantity (#3), Unit of Labor per each (#4), the Vendor Name and Pricing (#5). This estimating spreadsheet from MEP Academy automatically picks the lowest bidder, but can be overwritten by the estimator by entering a different value in the “Plug or Quote” box highlighted in yellow.
There are several sources for equipment labor values. But none is better than the contractors own historical data of the actual time required to set a piece of HVAC equipment in place. Below is a list of published data on equipment rigging and setting time. Read carefully the information contained in each reference as to what the labor units include and exclude, so that you can make any necessary adjustments.
MCAA (The Mechanical Contractors Association of America)
MCAA
MCA publishes labor hours for various pieces of HVAC equipment such as, Air Handlers, Chillers, Pumps, Cooling Towers and accessories. Each category of HVAC equipment has a range of sizes with varying amounts of labor required to set in place. Depending on the geographical location of your project, you will apply a factor to these values. Members get access to their online database of labor.
SMACNA (Sheet Metal and Air Conditioning Contractors National Association)
SMACNA publishes labor units for sheet metal duct and fittings in addition to certain HVAC equipment and accessories based on National averages. Air Conditioning Units, Coils, Fans, Filters, Sound Traps and miscellaneous items are available with various units of labor based on the size and or weight of the item. The SMACNA labor manual also provides a means to adjust labor based on difficult and very difficult conditions. The labor data was derived from surveys of sheet metal and air conditioning contractors in the United States and Canada, which included data from actual projects.
RS Means (Gordian)
Gordian publishes material and labor values for a wide range of construction components and assemblies for all trades. Many municipalities use the Gordian system for their procurement of construction services. The material and labor database is maintained and updated regularly by the Gordian Group.
PHCC publishes labor data which you can purchase. Their database covers a wide range of pipe, valves and fittings in addition to some equipment.
Company Historical Data
Historical Data that your company keeps from projects that have been completed is the best data available for your estimates. The problem is that most companies done take the time or effort to document these values, so they will need to rely on one or more of the industry published databases mentioned above for their benchmark labor.
If your company doesn’t keep track of the time it takes to rig and set in place the various pieces of HVAC equipment, I would suggest starting such effort in order to understand what it takes in the way of man hours and effort. It doesn’t matter what some industry database says it should take if your company can do it faster or slower than the published productivity rate. So begin to establish a company standard with the cooperation of your project managers and field personnel to record the time it takes to rig and set equipment and the various factors and conditions involved.
Basic Assumptions in Published Labor Databases
The industry published labor data for the time required to rig and set HVAC equipment is based on certain assumptions which are usually listed at the beginning of their labor manuals. Be sure to read any of the footnotes (MCA) or Correction Factors (SMACNA) on any of the equipment labor tables contained within these industry databases, as they will indicate any additional conditions or assumptions to be aware of. Assumptions might include some of the following which you should be thinking about when you go to labor the equipment and accessories.
Part of the process of dealing with equipment and accessories is the unloading, stockpiling, assembling, erecting and preparing the equipment for startup and testing. Depending on how your company prefers to allocate their labor, there might be a separate category of labor called material handling in which different pay rates are utilized.
Things to Consider When Figuring Equipment Labor
Location of Equipment
The industry equipment labor databases assume that the equipment will be within a certain distance from where it is to be installed, such as with MCA it’s assumed to be received within 100 feet from its final destination.
Size and Weight of HVAC Equipment
Equipment that weights under 250 Lbs (per MCA) is considered to be handled by a two person crew with the use of chain falls, hi-jacks or similar tools.
Chain Falls
Equipment that is over 250 Lbs might require a Roustabout, chain falls, crane, forklift, lift jacks, rollers, etc. to move them and get them in place. Below is a Genie Lift with varying capacity based on the model you own.
Genie Lift
How heavy is the equipment? Cooling Towers, Chillers, Large Boilers and Air Handlers will require rigging by a crane, forklift or helicopter depending on its location in the building or on the roof. Is the physical size of the equipment too large to be handled safely by workers? Will you need equipment rollers or the use of a hoist? Does the equipment come in several pieces in order for it to fit on a truck from the factory?
roustabout
You must become familiar with each piece of equipment and what is required to get it rigged and set in the location shown on the drawings. Is the equipment located indoors or outdoors?
Access to Equipment Location
How will the equipment get into its designated location?
If it is an existing building will the equipment fit in the service elevator or through doorways to its final resting spot?
Does the equipment easily breakdown into smaller pieces for rigging?
Is there room for a crane to setup on the side of the building closet to the equipment?
Do you need a street closer permit in order to block traffic during the rig so the crane can setup in the street?
Are there electrical overhead wires preventing a crane from operating in the area?
Do you need a helicopter?
Do you have to move other equipment or services to get your equipment in position?
Above are just a few of the things to think about when laboring equipment. You will need to adjust the standard labor based on the perceived risk and jobsite conditioned expected to be encountered during construction.
Method of Support
Is the equipment hung from above or set on the floor or roof? Does the equipment sit on vibration isolation? Do you need to build a support frame to hold the equipment, or does the equipment come with its own supports? Are seismic restraints required, as they add additional time to your equipment setting labor because of the additional time to install the restraints? Look at the detail pages on the drawings to find any engineered attachment or support methods.
Equipment Accessories
Does the equipment come with parts unattached for field assembly? Large filter racks need to be built up in place and then have their filters inserted. Sound traps can come with many modules needing assembling. Economizers are sometimes shipped loose and need to be attached. Backdraft dampers and roof curbs for exhaust fans. Vibration isolators for all types of equipment are a separate component that gets installed with the equipment. Cooling towers have ladders, motor davits and vibration isolators that ship separately.
HVAC Equipment Accessories
Multiple Pieces
Does the equipment come in several pieces because they are too large to ship in one piece, or are too large to fit through an existing doorway? Air handlers can be shipped broken down into fan, coil and filter sections all separated for easy shipment and field assembly. Cooling towers and fluid coolers also come in multiple sections. Talk to your vendor about how they plan to ship any large equipment that could possibly come in multiple pieces.
Crew Size
How many men are required to rig and set in place each piece of equipment? Composite crews made up of piping and sheet metal union workers will set anything that has piping and sheet metal attached to it, each union claiming a part of the work. As such, any piece of equipment that has only sheet metal attached will be claimed by the sheet metal union and vice versus for the piping union. If you work for a non-union company then worrying about jurisdictional labor allocation isn’t a problem. (See chapter on Labor Crew Size)
What Information Should You Record
Most of the information that you will need to labor the equipment can be found on the equipment schedule of the plans and specifications, or from the equipment submittal of the manufacture. Below is a list of a few items and what characteristics you might list for each piece of equipment on your estimating spreadsheet to help you provide a value for labor.
Air Compressors: List the HP (Horsepower), Receiver Capacity, Dimensions and Weight.
Air Conditioners: List the type, Tons, CFM (Cubic Feet per Minute), Dimensions and Weight. Types might include “Self-Contained”, “Water-Cooled Vertical”, “Packaged Rooftop Gas/Electric”
Air Handlers: List the type, CFM, Dimensions and Weight. Types may include Multi-Zone, Floor or Ceiling mounted, Custom, Roof Mounted.
Boilers: List the Type, HP (horse power), If steam Lbs/Hr, BTUH (BTU per Hour), Weight.
Chemical Feeders: Tank Capacity, size and weight
Chillers: Type, Tons, Air or Water-Cooled, Accessories
Coils: Type, Area FT2, Dimensions, rows of coils and weight.
Compressors: Type, Tons and weight
Condensate Return System: GPM (Gallons per Minute), Dimension and weight.
Condensers: Type, Tons, Dimensions and weight
HVAC Equipment Tab – Estimating Spreadsheet
Equipment labor should be applied to every piece of equipment and accessories that the field labor will be required to rig and anchor in place, whether fasten to the ground or hung in the air, or sitting on the roof. Your estimating spreadsheet should allow for conveniently allocating hours for each piece of equipment alongside its pricing.
HVAC Equipment Spreadsheet
HVAC contractors can provide both the sheet metal and HVAC piping requirements for a project. Some pieces of equipment will require a composite labor crew; especially if they’re a union company with define roles for each trade. Equipment that has water or refrigerant connected to it along with sheet metal may require a composite labor crew.
Enter the quantity and description of the equipment, and then enter the unit of labor required for each piece of equipment. If you have four (4) Rooftop Upblast Exhaust Fans that sit on a roof curb, you might enter 4 hours each if they’re smaller units, which would give you a total of 16 sheet metal hours for the 4 small exhaust fans.
Retrofit Projects
If you are bidding on a project that is within an existing building, then you will need to consider additional labor items. Ducts and pipes will need to be disconnected from the HVAC equipment. Water will need to be drained out of any pipes connected to any equipment receiving any form of water or steam service.
To get large pieces of equipment out of existing spaces, often requires that it be taken apart or cut into pieces. If your company doesn’t do this type of work, there are specialty companies that you can subcontract this work to. If you are bidding on a turn-key project, one in where your company is responsible for all trades, then you will need to get other companies involved, this usually occurs under the design/build method of construction contracts.
What’s Not Included in the Labor Units
Start Up & Testing of Equipment
The time for startup and testing is a separate labor task that is usually done by trained technicians different than those installing the equipment. These specialized individuals are familiar with the procedures and documentation required for starting up and testing HVAC equipment.
Air and Water Balance
Often the specification will require a third party to perform the air and water balancing in order to avoid conflicts of interest that occur when the contractor self performs this work. Typically the specifications will call for the Air and Water Balance Company to use NEBB or ABBC certified technicians to perform the work.
Equipment Identification
Each piece of HVAC, Plumbing or Electrical equipment will get an identification tag that identifies what the equipment is, along with some of its capacity information and possibly the area it serves.
HVAC Equipment Tags
There will be a unit cost for material and labor for every equipment ID tag. A field laborer will need to fasten the equipment tag somewhere visible to the maintenance staff when accessing the equipment. The background and lettering color maybe dictated by the specifications and is often provided on some form of laminated plastic. Put this requirement on the sheet metal specialties tab of your estimating spreadsheet. (see chapter on Sheet Metal Specialties)
Sheet Metal Specialties – MEP Academy Estimating Spreadsheet
Get a copy of the MEP Academy Estimating Spreadsheet.
Now that you have figured the labor to set each piece of equipment, you should have a good idea as to what rental equipment will be required for each task. Did you figure setting some of the equipment with a crane? Do you need a forklift to move materials around or remove a piece of equipment from a delivery truck, or to raise a heavy piece of equipment in the air or reach the second floor from the outside of the building in new construction? Will the works need a scissor lift to hang a section of piping or ductwork?
These are the questions you will need to ask yourself or others when analyzing the field labor required to rig and set the HVAC equipment. Using the proper tools makes for a more efficient installation and a safer project. The total cost for equipment rentals appears under other cost on the estimate summary sheet of your spreadsheet.
You must have a good idea how long you will need the rental piece of equipment, as rental rates are cheaper the longer you rent them, but you don’t won’t to rent them longer then you need them ,as this would make your bid less competitive.
Helicopters
Sometimes the only method of safely getting equipment to its point of use is by helicopter. Helicopters are useful in placing equipment that sits far from the side of the building, or when there are multiple buildings. These are some of the cases where a helicopter will be more feasible than a crane. Call an get a quote for any job that you are bidding that may require a helicopter to see how it compares to the use of a crane.
In the video below you’ll see Air Conditioning units being helicoptered onto AC Adapter curbs. Adapter curbs are used to match up the existing curbs supply air and return air configuration with the new A/C units supply & return air configuration. This video is for just two air conditioners, but we have rigged more than 100 air conditioners in a day using a helicopter.
Helicopter Lift
For larger HVAC units you would need to a much larger helicopter such as that provided by Erickson Crane. For Large and heavy HVAC units you would need the S-64 Aircrane from Erickson which has the capacity to lift up to 25,000 pounds. (See the video below for the S-64 Aircrane) They have smaller helicopter that will do up to 7,000 pounds.
Erickson Crane for Large Loads
Cranes
Cranes are good for a wide range of equipment and purposes. If you have something located on a roof that is too heavy to carry safely up the stairway you might need a crane. Anything from a small sign crane to a large built-up crane can be secured from one of many crane rental companies. If conditions are such that a crane cannot reach the roof or isn’t feasible you may need to call a helicopter operator who specializes in HVAC equipment rigs. Sometimes the use of a helicopter makes sense over a crane, because of site logistic, such as having many buildings spread out over a campus, which would require a crane to move and setup multiple times.
Watch this video of a 550 Ton Hydraulic Crane rigging large Air Conditioners off and onto this building. It takes considerable effort to put this crane together to handle the weight of these air conditioners and for the crane to reach the units. Of course not all cranes have to be built up like this one, but this shows you the cost involved when rigging heavy HVAC equipment that is located far from the perimeter of the building.
550 Ton Hydraulic Crane
Prices and regulatory requirements vary from location to location, so call your crane or helicopter company with the address of the building and the size and weight of the heaviest piece of equipment. Also, you will need to let them know how many equipment picks you have going up and down, the location of the equipment on the building. The distance from where the crane can set up to the location where the equipment will be set and the height of the building affects the size of the crane and the cost.
Below is a quick video of the crane rig of several rooftop air-cooled chillers. The workers first grind off the welds that are holding the existing air-cooled chillers to the support steel.
Air-Cooled Chiller
Crane Charts
The size of the crane required is based on the weight of the HVAC equipment and the height (Vertical distance) and (horizontal distance) to where the unit will sit on the building. As shown in the Crane Chart below for a 550-Ton crane, there is a point at which the crane can’t reach (shown in pink) without adding additional jibs or extending arms if available.
The crane rental companies use software that determines the required crane size based on your rigging requirements. The crane charts provide a quick visual representation of the various limitations based on vertical and horizontal distances. Check Bragg Cranes website for additional information on cranes and their rigging capacities.
Crane Chart
Scissor Lifts
Scissor lifts are useful when the working height becomes unsafe for ladders. In construction safety should always be the priority, so you want to make sure your workers are provided with adequate tools to do their jobs. Definitely anything heavy and awkward that is to be installed over 15 feet in height will need a scissor lift or some other raised platform to work from.
You will need to determine how many hours you have in the area with the high working environment, and how many workers will be doing that task, so you can determine how many days, weeks or months you will need the rental equipment. This is one of the reasons we breakdown a takeoff into different areas and task, so that we can analyze labor and rental equipment requirements.
Watch the video below to see how they operate.
Scissor Lift
Forklifts
Equipment being delivered to the jobsite that will not be rigged with a crane the day it arrives will need to be taken off the truck and stored until rig day. Heavy equipment will require something like a forklift to remove it from the truck and move it around the project site for temporary storage. Forklifts are good for moving heavy pieces of equipment safely around the jobsite, or for loading pallets of material from a truck to a laydown area. They are also good for loading equipment or material onto the second floor if within reach from ground level.
Forklift
Boom Lifts
These are used where a scissor lift won’t work. Scissor lifts are good for going up and down, but a boom lift does that and more. The boom lift can go up and pivot over objects to reach areas that a scissor lift can’t watch the enclosed video to see the versatility of a boom lift.
Articulating Booms
Articulated Booms provide additional versatility (watch video below). Check with your rental equipment provider to see what the equipment capabilities are in your area. This particular articulating boom lift is in Australia, but similar boom lifts are available worldwide. The video below is a little dramatic, but hold out to see just how well this equipment works.
Articulated Boom
Backhoes / Excavators
If you will be digging a ditch for underground pipes or ducts, then a backhoe might be needed. If you subcontract all of your excavation and backfill you won’t need to worry about this rental equipment. Make sure to include the hourly cost of the backhoe operator if you don’t have someone capable of doing it.
Backhoe Excavators
Welders
If you plan on doing any pipe, duct or support steel welding, make sure to include the cost for welders. Gas or electric welders can be rented for the day, week or month.
Air Compressors
Some tools require pressurized air to make them operate including some jack hammers.
Groover’s
If you will be fabricating grooved pipe onsite for grooved type connections then having this tool at the site will save time and money.
Storage Containers
Each project has different requirements, but most new construction projects will need a storage bin to lock up your materials and tools, otherwise they could be stolen, or you would need to handle them every time you arrived and left the project site.
Miscellaneous Equipment
This piece of rental equipment helps save on the cost of using a larger crane to reach far from the perimeter. By using a smaller crane that to rig the HVAC units onto the perimeter of the roof at the point closest to the edge of the roof, then using this piece of rental equipment to roll the HVAC units into place, will save money by not having to use a larger carne.
Misc Rental Equipment
As an estimator you should search for better ways to do things that will make you more competitive, this is just one way.
Contractor Owned Rental Equipment
If your company owns a piece of equipment you could normally rent it, then charging it to the project at a reasonable rental rate is one way to recoup its cost.
You might be thinking, why don’t I leave out the cost of the company owned rental equipment and make our bid lower. Every piece of company owned equipment has value that is depreciating as it gets older, and it cost money to operate and maintain. So if you don’t charge for the equipment you would theoretically be losing money. The cost to operate that piece of equipment has to come from somewhere and rightly it should come from the job that is benefiting from its use. Gas, oil, tires, parts and maintenance will be expended in the use of that equipment. Make it a happen to charge for company owned rental equipment unless its cost recovery is included in your labor burden rates or some other recovery line item.
There are many more pieces of rental equipment that you will encounter, but the list below will get you started. List all those pieces of rental equipment that you normally rent on your rental form in your estimating spreadsheet along with their rental rates for either daily, weekly or monthly.
You should setup your rental sheet on your estimating spreadsheet with the rental equipment that you rent most often. This will save you time from having to re-enter the data over again. List the rental equipment and the rate you are charged for the duration that you expect to use for this project. If you have 240 hours of work in a high bay area that requires a scissor lift and a two person crew, that is equivalent to three weeks of rental. In that case I would carry a months’ worth of rental for a scissor lift.
If you have many pieces of equipment coming from various vendors, all to be rigged onto the roof, then you might want to receive all the equipment into your warehouse or pay the crane company extra to store the equipment until rig day.
Sources of Rental Rates
There are numerous sources for equipment rental rates.
Local Rental Company
The best source of course is your local equipment rental company, the one you most often and trust. If the project is far from your normal rental company, then you will want to get prices from rental companies in the area where the project is being built or renovated.
MCA (Mechanical Contractors Association)
MCA publishes a book of rental rates for various pieces of equipment and tools. This is a good source if you own your own equipment and are trying to negotiate a fair rental rate with an owner or GC (General Contractor). Remember just because you own a piece of equipment, doesn’t mean you can’t charge for it. The cost should be included in your change-orders if the contract allows.
Army Corp of Engineers
The Army Corp of Engineers publishes rates for various rental equipment.
In order to do a takeoff, you will need to be able to understand what rectangular duct and fittings look like and how they are represented on the drawings. They can be drawn either as a single line or as a double line, making their appearance much different. We will show you both ways so you can identify any fitting in its single line or double line format.
Engineers use software programs such as AutoCAD or BIM (Building Information Modeling) that have standard duct and fitting symbols, in addition they have the ability to create their own representations of what duct and fittings look like on the drawings, but once you know what to look for you can identify the slight differences.
Rectangular Ducts
Ducts come in various lengths depending on the fabrication equipment available to the contractor. For those sheet metal fabrication shops that have a coil line where sheet metal comes from the manufacturer in large coils of various gages (Thickness) the cost of fabrication can be reduced because of automation. See Sheet Metal Shop Fabrication course for more information.
Typical sheet metal coil widths are 36”, 48”, 60” and 72”. Sheet metal can also be purchased in flat sheets typically 36” x 96”, 36” x 120”, 48” x 96”, 48” x 120”, 60” x 96” and 60” x 120”. Standard duct lengths can be 4 or 5 feet long from joint to joint, not taking in to consideration the loss of length due to the joint itself, unless you’re using a proprietary slip on joint.
If the standard widths of coils and flat stock are 36”, 48” and 60” then this is usually what the standard lengths of sheet metal ducts you will be using in commercial construction. You want to optimize the length of the duct so as to avoid extra material handling which increases your labor cost.
Sheet Metal Material – Flat Stock
Rectangular duct is often more expensive to make then the equivalent round duct. Round spiral duct is made using a spiral machine then spins out round duct from a coil of sheet metal. Because round comes in standard sizes and is easily spun the cost tends to be less than its rectangular equivalent.
Duct Joints and Seams
Knowing the length of a standard sheet metal coil line duct will help you determine how many short pieces you have when doing a takeoff. A short piece is a piece of duct shorter than your standard length. This short piece will have to be done my hand in the shop instead of being put through the automated coil line. Short pieces cost more per pound than does coil line duct. It’s less expensive for the automated coil line to make a piece of duct then to have it made with manual labor.
Ducts can be shipped fully assembled or in knocked down “L” sections. Having the duct shipped in “L” sections (knocked down) allows for more sheet metal to be shipped as it is easy to nest them together. This will also increase the field labor as they now have to knock together the “L” sections of duct.
Joints
The duct joint is that portion of the duct that attaches to the following section of duct or fitting. Joints can be made from the section of duct or fitting or can be an attachment to the end that facilitates the connection of two pieces. There are various types of joints, the most common being; TDC (transverse duct connector), Ductmate, S&D (Slip and Drive), Welded, and Standing S and Drive. (See Chapter on Sheet Metal Joints)
Seams
The seam is that part of the duct that attaches to another part of itself to assemble the duct section or fitting together. Seam types vary based on pressure class and the largest dimension of the ductwork, your company preference or jurisdictional requirements. Some of the most common seam types are the Pittsburgh Seam, Snap Lock, Gore Lock or Welded Seam. (See Chapter on Sheet Metal Seams)
Rectangular Fittings
Rectangular fittings cost more than rectangular straight duct because of the additional labor to cut and assemble each piece of the fitting. Fittings require multiple pieces to be cut form the metal then assembled into the final shape. We will go over the various types of fittings most commonly found in commercial construction.
Starting Fittings
Whenever you have a piece of duct tapping into the side of another duct you will need a starting fitting. This starting fitting allows you to firmly attach to the other piece of duct and provide for a proper seal, so as to avoid leakage. Ducts that leak are effectively losing money, as the cost to cool or heat the air is lost to the attic or outside.
Each of these starting fittings will get you connected to the side of the rectangular duct or round duct, just like in the chapter on round duct.
Rectangular on Rectangular
You want to make sure that the rectangular duct you’re attaching to is at least a couple inches greater than the duct that is being attached. For example of the main rectangular duct was 20 inches in depth, then you would use an 18 inch or smaller in depth branch starting fitting. This allows space for the duct seams. Remember that the first dimension that you see belongs to the side that is visible in the view.
45 Degree Tap
Using a 45 degree tap provides better flow characteristics than a straight tap. These are commonly used on the supply side, while the straight tap is commonly found on the return or exhaust ducts.
Rectangular Tap
Square to Round Tap
These are often used when the depth of the rectangular duct is less than the round size of the branch being connected. For example this allows for a 12” round spiral duct to be attached to the side of a rectangular duct that is only 10” high. This type of fitting also offers the additional benefit of providing better air flow characteristics.
Square to Round Tap
Rectangular Tap on Round Duct
This is often used to mounted rectangular supply grilles on the side of a large round main duct. You may see this arrangement where there are no ceilings installed, such as; Gymnasiums, Restaurants, Warehouses, etc.
Rectangular on Round
Square Elbow with Turning Vanes
The elbow is found where you want to make a 90 degree turn. The use of turning vanes allows for the smooth change in direction of the air, instead of it pounding against the side of the fitting. Turning vanes are mostly used on the supply air side of the system, while elbows without turning vanes are often used for negative air systems like Return Air and Exhaust. Turning vanes come in various designs including single thickness, double wall, and the expensive double wall acoustical turning vane.
Square Elbow with Turning Vanes
Here is what an elbow with turning vanes look like on a drawing drawn with double lines.
Turning Vanes
The square elbow has four basic pieces; Cheek, Throat, Heel and Turning Vanes.
Parts of a Square Elbow
There are several types of turning vanes used in elbows. You should verify with the specifications as to the requirements of the turning vanes on your project. The most common turning vanes are; single wall, double wall and acoustical turning vanes.
Single Wall Turning Vanes
Single Wall Turning Vanes
Double Wall Turning Vanes
Double Wall Turning Vanes
90 Degree Radius Elbow
Similar to the square elbow in that it provides a 90 degree turn in your sheet metal ductwork. Instead of an abrupt turn like the square elbow, this elbow provides for a 90 degree radius turn. Turning vanes can be added to this fitting also, but it’s not as commonly specified. The 90 Degree Radius Elbow takes up more space when turning then for the same size 90 Degree Square Elbow.
In order to route duct through buildings and around obstructions and other utilities you will need to offset as required. The 45 degree angle is commonly used to offset around obstructions.
45-Degree Angle
Bullhead Tee – Double Elbows
The use of this fitting allows for the simultaneous 90 degree turn in opposite directions. This can be done using either hard square elbows or radius elbows.
Double ElbowsBullhead Tee
Transitions – Eccentric & Concentric
A transition allows you to reduce the size of your ductwork. This is done when CFM (Cubic Feet per Minute), the volume of air has been reduced in the duct to where it makes sense to use a smaller size. There are several standard transition configurations; eccentric is where you transition one side only, and concentric where you converge two sides to maintain a centerline path for the air flow.
Transitions
Offsets – Ogee’s
The use of an offset allows for the designer to get around various aspects of the built environment such as; plumbing pipes, structural elements, electrical conduits, fire sprinklers, lights, other ductwork, etc.
Similar to the previous square to round tap above, this fitting is used on the run instead of tapping into the side of the duct. Converting to round duct from rectangular duct is usually a more cost effective solution and allows for the use of flexible duct connections to a piece of air distribution.
Square to Round FittingSquare to Round
Transfer Duct
The purpose of the transfer duct is to allow air that is trapped in a space by a full height wall, to make its way through that wall to the other side where it will return back to the system, whether an exhaust fan or air conditioner of some sort. This often occurs in non-ducted return air systems.
Lined Transfer Duct (Good for Sound Attenuation)
Return Air Sound Boot
The return air boot helps reduce noise transmission from one space to another with the use of lined duct attached to a 90 degree elbow.
Return Air Sound Boot
Louver with Plenum
A louver serves the purpose of providing weatherproof openings in the building structure to allow air to enter or be exhausted from the building. You could find exhaust ducts terminating at a louver or outside air being brought into the building to provide code required ventilation (fresh air) for the building occupants.
Louver with Sheet Metal Plenum
Volume Dampers
Volume dampers provide an important role in the air balancing of the system. Each branch duct should have a volume damper that allows the volume of air to be adjusted. The engineer designs the HVAC system with a specific CFM (Air Volume) for each space in the building and for each piece of air distribution. The contractor will hire or self-perform an air balance to get the system to provide the quantity of air as indicated on the drawings by the design engineer.
The volume damper is used during air balancing to adjust the volume of air that comes out of the air distribution device. It is not good engineering practice to try an use the air distribution device as a volume damper, as the closer the restriction is to the air distribution device the greater the noise will be to the space.
Rectangular Volume Damper
Duct Liner
Sheet metal is either wrapped with insulation or lined with insulation. Liner can be used for either thermal or acoustical reasons. If the HVAC air duct is traveling through an unconditioned space then the ductwork will need to be wrapped or lined with insulation to avoid the loss or gain or heat. This is a code requirement and is meant to avoid a loss in energy. Lining a duct is also used to eliminate or reduce the transmission of noise. Watch this video to see how the liner is fastened with pins welded to the metal. A version of this machine can be installed in-line with a fully automated coil line.
Pin Spotter for attaching Liner to duct
Duct liner comes in various thicknesses depending on the thermal or acoustical properties required. Common sizes include 1/2”, 1”, 1-1/2” and 2” liner. Liner is attached in the sheet metal fabrication shop with the use of pins and adhesive. (See Chapter of Sheet Metal Coil Line for automated process)
Double Wall Duct with Perforated Liner
To reduce noise within and through ducts and fittings they are lined with sound attenuating (noise reduction) duct liner (#2) and inner wall of perforated liner (#3). You would have your external sheet metal duct or fitting material (#1) with acoustical liner (#2) fasten with adhesive and sandwiched with the perforated metal (#3). This is done in all shapes of ductwork and fittings, including rectangular, round and oval.
Double-Wall Duct with Perforated Metal Liner
The noise is attenuated by the small holes which attract the noise into the fiberglass insulation that is sandwiched between the inner and outer wall. It’s obvious that this type of duct is going to cost much more than the standard ductwork. You may find this required for the first 25 feet more or less from any noise generating equipment, like a fan within an air handler. Check the specifications and drawing note and details.
Duct Wrap – Insulation
Duct wrap as mention above is used for its thermal protective properties. Keeping heat from escaping or entering the sheet metal duct is important to preserve the usage of energy. Duct wrap usually comes in the following sizes based on the R-Value required to meet the local building or energy code; 1”, 1-1/2”, 2” and 3”. The insulating of ductwork on large commercial projects is usually handled by a subcontractor of the HVAC contractor. These contractors specialize in the insulation of ductwork and piping related to the HVAC and Plumbing industry.
Sealants
Sealants are used to ensure a proper seal at seams and joints. It’s important that construction of the ductwork that is carrying conditioned air is air tight. There are various types of sealer used; duct tape, silicone, hardcast, etc.
Turning Vanes
The use of turning vanes provides for better air flow and fluid dynamics. Turning vanes are comprised of the vane rail (#2) which comes in coils (#1) and the turning vane (#3). When these two components are assembled you will have the turning vane assembly (#4) which then gets inserted into the elbow or fitting. The parts shown here are from Hardcast by the Carlsile Company.
