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.
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.
Round fitting types and methods of construction can vary by region and between companies. Engineers use software programs that have standardized duct and fitting symbols, in addition to 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 between designs.
Depending on the situation ducts either start at some cooling or heating source air conditioner, air handler or an HVAC accessory like a VAV terminal, or transition from a rectangular duct as in a square to round fitting.
If the round doesn’t start from a piece of equipment or from a square to round, then it will need some form of starting fitting. Manufactures make various types and connection methods, so you need to become familiar of what is commonly used in your area.
Round Duct Types
Round duct is manufactured with various seam types, the most common being spiral or snap lock.
Spiral Round Ducts
Round duct is used to connect between fittings, accessories and flex duct. Manufactures usually stock standard lengths, but if you have your own spiral machine you can fabricate any length.
Spiral duct is not limited in length, except as required to fit on a truck or in an elevator, or as needed for the insertion of a fitting. Reinforcement rings are generally not required for positive pressure and low negative pressure round ducts. The use of rings helps maintain the roundness of the duct as the sizes get larger.
spiral duct
Longitudinal Seam Round Duct
In addition to the spiral seam there are various other types of seams that run straight from one end to the other (longitudinally), such as a longitudinal welded seam as shown in the video below. The video quality isn’t the best but it shows how you can weld galvanized and stainless steel round ductwork, and how to adjust the machine for various sizes.
Welded Longitudinal Seam
There is also a snap lock version of the longitudinal seam as shown in this next video. This particular type of round duct has an internal gasket that makes the seal.
Snap Lock Longitudinal Seam
Sheet Metal Rollers
When the use of round spiral is not allowed the use of longitudinal welded round duct is required, a piece of fabrication equipment that can roll a piece of flat stock into the required round size.
sheet metal roller
Specialty exhaust systems that require a secure seam without ridges can be made with a longitudinal seam.
sheet metal roller machine
Watch this Sheet Metal Roller video to see a sheet metal roller in action.
Sheet Metal Rollers
Longitudinal vs Spiral Seam
Spiral allows for lighter gages then longitudinal seams when using Unreinforced Round duct as shown in the SMACNA table below. You can see that from 4” to 14” round (Column #1), both Longitudinal Seam (Column #2) and Spiral Seam (Column #3) require the same 28 gage minimum. But, spiral seam can use 26 gage from size 16” to 24” round, while longitudinal seam is limited to a maximum of 18” round when using 26 ga. This indicates that the spiral seam is stronger and more rigid then a longitudinal seam.
You can also see in the table that the larger the round size the greater or thicker the metal gage required.
Unreinforced Round Duct
Special Round Ducts and Fittings
There are various manufactures that make proprietary systems that are meant to save labor such as the Eastern Sheet Metal’s gasket fitting system. The rubber gasket provides a tight seal, making additional sealing unnecessary. Watch the enclosed video to see how easy the ductwork goes together. They also have a double-wall version, in addition to a single and double-wall flanged system, and one for oval.
Single Wall Round Duct with Gaskets
Double-Wall Duct & Fittings
In some cases engineers will specify double-wall duct, often when noise is an issue, but it also provides thermal properties. Double-wall duct comes in round or oval sizes with either a solid inner wall or a perforated inner liner, with insulation sandwiched in between the inner and outer wall.
The outer duct can be purchased with three different seams, spiral lockseam, spiral lockseam with a standing rib, and longitudinal seam.
This next video shows how one shop fabricates double-wall duct with a perforated inner wall and lined with fiberglass insulation. The perforated inner wall is made from a skinny coil of material similar to that of spiral duct.
Making Double Wall Spiral
Engineers will also specify that the duct be made by a particular manufacture so that a certain level of quality can be assured to the owner.
Lined Round Spiral Duct and Fittings
In order to provide acoustical properties, which is the ability to attenuate or reduce sound transmission, lined round spiral duct can be used by adding liner to the interior of the duct. Watch the video below of the John Mansville Spiracoustic Plus liner material being added very easily to spiral duct and fittings.
Fabric Duct
There are special cases where instead of sheet metal you can use fabric ductwork such as made by DuctSox. Where you have long straight runs of exposed ductwork the application of DuctSox may make sense, such as gymnasiums and indoor pools.
You have the option of having the air dispersed through linear vents, fixed orifices, fixed nozzles or adjustable nozzles.
They can come in various color options, and can have zippered sections. Companies can also have their logo imprinted on the fabric or pick from various patterns.
The fabric can be supported by an internal metal ring which provides tension to keep the fabrics shape, or without any internal metal ring in which case when the air is shutoff, the fabric will collapse.
Fabric Duct Hanging Methods
You can use an external cable to suspend the fabric sox or a channel that allows you to pull the fabric like a curtain along the suspended railway.
Applications
Fabric ducts can be used in Gymnasiums, Warehouses, Manufacturing Facilities, Indoor Pools, Auditoriums, Schools, Malls, Restaurants and other exposed locations.
In a lot of these facilities the use of some form of man-lift or scissor lift will be required to reach the heights at which these fabric ducts get installed. Remember to always check the height at which your ductwork needs to be hung.
As shown below the DuctSox (#1) is used in a Gymnasium and is installed at 28’-1” above the floor, which would require some form of man-lift for the installation. The main supply air duct (#4) is run in galvanized rectangular ductwork, including the return air duct (#3).
Duct Sox Elevation
The video below is another brand of fabric ductwork which shows workers installing the duct using a scissor lift.
Fabric Duct
Round Flexible Ducts
Flexible ducts come in various arrangements that include insulated and uninsulated, metallic and nonmetallic. The insulated version would be used to carry conditioned air or for the reduction of noise, while the uninsulated metallic would be used for non-condition exhaust air. The use of flexible duct should be kept to a minimum to avoid excessive pressure drop. Aluminum is the most commonly used material for metallic flexible ducts. Flexible ducts come in various lengths depending on manufacture.
The R-values of the insulated flexible ducts range from R4.2, R6 to R8. Flexible duct comes in lengths of 3, 6 and 25 feet with some manufactures, others may vary.
Flexible Duct Defined
Flexible ducts need to be supported according to the manufactures recommended method but not less than every 5 feet, including the maximum sag of 1/2” per foot between support hangers. This would allow maximum sag of 2-1/2” between two support hangers spaced 5 feet apart. The portion of the hanger that the flexible duct rest upon needs to be at least 1 inch wide to avoid the reduction of the internal diameter. This can be accomplished by a 1 inch wide hanger strap or by providing a saddle for the flexible duct. The size of the saddle would need to be half the circumference of the outside diameter of the flexible duct and sit at the bottom half.
Draw bands must be used to secure nonmetallic flexible ducts to a sheet metal sleeve or collar.
Flex Duct Bands
The most commonly used piece of flex duct is for the last 6 feet (2m) where a connection is made to a piece of air distribution. Some projects allow all of the low side ductwork to be run in flex. This is not the best approach due to many factors, one of them is static pressure loss.
Air Distribution Flexible Connection Detail
Watch this video for the correct methods of supporting flexible ductwork.
Flexible Duct Support
Insulated Aluminum Flex
Some projects may allow long runs of insulated aluminum flexible duct, but this is not good engineering practice due to the higher resistance created from through inner surface, which creates more static pressure losses and increased energy cost.
Insulated Aluminum Flex
Uninsulated Aluminum Flexible Duct
Often used for exhaust system that require a short run of duct.
Uninsulated Aluminum Flex
Start Collar
A round hole is cut into the side of a rectangular duct and the dove tails of the start collar are alternately bent perpendicular, one inside, one outside, and fasten with sheet metal screws and then sealer is applied.
Start Collar
Start Collar with Volume Damper
Often the start collar will have a volume damper included. Keeping the volume damper in the start collar and as far away from the air distribution will help reduce noise transmission through the grille into the room.
Start Collar with Volume DamperStart Collar with Volume Damper
Flat Saddle Tap
Instead of a spin-in or similar starting fitting, a flat saddle tap can be used to get round duct started from the side of a piece of rectangular duct. Available with a 45 or 90-degree branch.
This fitting is used in lieu of some form of a tee fitting. This will save having to cut the main round duct to install a Tee. This is a round on round fitting. Available with a 45 or 90-degree branch.
Radius Saddle Tap
Here is a short video on the basics of installing a saddletap. There are electric shears that would work much better than the manual shear that this gentlemen uses in this video. You can stop the video after 2 minutes 38 seconds.
Installing a Saddle Tap
Square to Round
When rectangular duct transitions to round duct on the straight run its called a square-to-round.
Square to Roundsquare to round example
90 Degree Elbow
Most turns will either be 90 degrees or 45 degrees. You don’t see a lot of odd angle elbows as they would be more of a custom made fitting and more expensive. Notice the crimped end on one end of the fitting.
90 degree Round Elbow
Elbows can come in many variations, from adjustable, stamped, pleated, spot welded or fully welded. Here is a video on how an adjustable elbow can be manipulated to create various angles.
90 Degree Adjustable Elbows
Sheet Metal Spiral Elbow Machine
There are machines that lock segments or sections of a fitting together to make a complete fitting. Some of these machines are referred to as Gore Lockers. Two segments are butted together and are spun around as their seams are locked together by the gore locking machine. For a multiple gore elbow this occurs with each piece until you get the quantity of gores required. This is common for adjustable gore elbows. It’s a good time to discuss the different types of elbows.
Spiral Elbow Machine
45 Degree Elbow
There are several different types of elbows based on seam and joint types. As you can see this fitting also has a crimped end allowing it to slip inside the next piece of duct.
45 Degree Elbow
Tee-Wye (T-Y)
These are used to make 45-degree branch connections. See the image above where the T-Wye reduces the main branch from 10” x 8” x 8”. Also shown above but not highlighted is an 8” x 8” x 8” Tee-Wye, can you find it. Also note that the acronym used for a this fitting may be spelled many different ways, but they all refer to the same fitting type such as; T-Y, T-Wye, Tee-Wye, etc .
Tee-Wye Fitting
Volume Dampers
Dampers are used to adjust the volume in ducts. These will be used by the air balancing personnel to set the CFM needed for the branch or main that has a manual volume damper.
Volume DamperVolume DampersVolume Damper Example
In the example above the volume damper controls the amount of air that air distribution diffuser CD-6 receives, in this case it indicates 500 CFM (cubic feet per minute)
Reducers
A reducer is used to change size of the duct run. The reduction in size can also be accomplished by using a reducing tee.
Round Reducer
Round Joint Types
Most low pressure round fittings will either have a crimped end or be coupling sized.
Crimped Ends
Crimped ends reduce the overall diameter just slightly so that the fitting or duct can slip into the next piece.
Crimped Joint
Round Couplings
Couplings slip inside the ends of two round ducts to be joined together and then sheet metal screws are fastened to hold it in place. Couplings could be required at a certain size such as connections 18” and larger. The shaded area in the image below is the coupling.
round coupling
Flanged Connections
There are many manufactures that provide various types of flanged connections like Ductmate™ Spiralmate™, see their website for more information and videos for various connections.
Welded Connections
The requirement for a welded duct connection can be found for kitchen grease exhaust systems or some industrial processes and laboratory exhaust systems. Some of the more commonly welded duct materials are galvanized steel, stainless steel and black iron. Joints are often butt welded or flanged.
Often welded kitchen exhaust systems will use stainless steel where exposed to view and black iron for the hidden duct to the grease exhaust fan. Grease exhaust ducts need clean-out doors every so often as required by code for access for cleaning. (Also see chapter on Grease Exhaust Systems).
FRP – Fiberglass Reinforced Duct
Used in industrial processes to exhaust corrosive fumes such as solvent or acid exhaust systems. You can spend your life in the HVAC business and never be involved in a project that requires this material, but watch the enclosed short video so you understand what is involved.
The Proper Use of Round Fittings
There is more than one way to make a reduction or branch connection. As the following example shows you can use two different ways to accomplish the same thing. In the example we have a round main duct that branches into two 12” round branches. You can either use a 14” x 12” x 12” Tee-Wye or you can use a 14” – 12” reducer with a 12” saddle-tap.
Various Fitting Options
Various Fitting Options
Reducing Tee-Wye Fitting (Best Option)Round Saddle Tap and Reducer (Requires two additional pieces)
In the case above it would be best to use the T-WYE as it is one less connection. Use a T-Wye when the main duct changes sizes, and use saddle-taps when the main remains the same size as shown below. Using the saddle tap and the reducer in the above scenario would require and extra cut of the duct and two fittings, instead one T-Wye fitting.
45-Degree Radius Saddle Taps45 Degree Saddle Tap Example
In lieu of a full body fitting you can use a saddle-tap which allows the main duct to remain the same size without having to cut-in a fitting. A saddle-tap does just as its name implies, it saddles the main round duct. This is accomplished by cutting a hole in the main duct where the branch is to occur and then the saddle-tap is fastened with sheet metal screws and then sealed to provide an airtight assembly.
Round Fitting Usage
Round Starting Fittings
Whenever you have a piece of duct tapping into the side of another duct you will need a starting fitting if you are not using a whole body fitting of the same shape.
Round on Rectangular Duct
So, if you have a round duct branching off of a rectangular duct you might use one of the following;
Options for branch connections
Options for branch connections
Spin-in
Spin-in with damper
Dove-tail spin-in
Scoop tap-in
Flat 45 Degree Saddle-tap
Flat Straight Saddle-tap
Each of these starting fittings will get you connected to the side of the rectangular duct and then capable of connecting another round piece to that fitting, such as a length of spiral duct.
Round on Round Duct
Fitting Usage Example
Straight Saddle-tap
45 Degree Saddle-tap
Tee-Wye
Single Line Duct Design
Most often you will find that the duct design is done in a single line style, where the actual scale width of the duct is not represented.
In the above example the yellow dot highlights a fitting that may not be feasible to fabricate and what could be a better selection is a Tee-Wye instead of a bullhead tee as shown.
In the above example the Red dot highlights a typical Tee-Wye except that is usually preferable if possible to have the branch that angles off in a 45 degree to be the same size or smaller then the reducing run dimension, in this case the Tee-Wye is a 12” x 8” x 10”. It would be better to use a 12” x 10” x 8” if possible.
In the above example the Green Dot highlights an expensive fitting as opposed to a simple spin-in. What is actually represented by the symbol is a type of tap/Square-to-Round all in one fitting.
Square to Round Example
There are many different ways to make a branch connection in round duct from a full body fitting like a Tee to a saddle-tap which only requires a hole in the side of the duct big enough for the connection outlet size.
45 Degree Saddle Tap Examplestraight saddle tap
Often there will be several methods to accomplish the same branch takeoff or reduction in size. Whether to use a fitting or some form of saddle-tap and reducer can depend on the specifications or your company preferences.
Reducing Tee-WyeRound Saddle Tap and Reducer
The above fitting accomplishes the provision of a branch connection and a size reduction in the run. This can also be accomplished by cutting an opening in the side of the main duct for a saddle-tap that provides for a branch connection and then a reducer to provide a reduction in size for the main run. The fitting is comprised of one piece while the other connection method requires two pieces, the saddle-tap and reducer.
Saddle-taps are an effective strategy when you have multiple taps on a main duct that doesn’t change in size on the run. For instance, if you had a main 20” spiral that had four 10” branches it would be best to use saddle-taps to avoid cutting the main for a Tee connection for each branches.
Round fittings will be represented on the drawings either in single or double line format. Either way the specifications will let you know what type of fittings are required.
Round fittings come in various construction seams and joints, which show be defined in the specifications.
We will show you where each of these fittings are used and the different ways they can be represented on engineered drawings.
Engineers or their CAD personnel may not show the fittings as you would actually build the duct. You have to read the specifications and look at the details to determine what is allowed.
Fully Welded Round Fittings
There will be projects that require a fully welded round system. This usually occurs where special an exhaust system contains flammable or noxious gases in the air stream.
Fully Welded Round Fittings
Gored Elbows
As shown in the image above these are fully welded 90 degree elbows with flanged joints. The seams are fully welded and the quantity of gores are indicated. There is a 5 and 7 gore elbow identified in the image above. When a greater radius turn is required the engineer will specify more gores for the elbow. This applies to any degree of elbow from the standard 45 and 90 degree elbows to custom angles such as 30 and 60 degrees.
5-Gore Elbow
Mitered elbows should comply with SMACNA table 3-1 below which sets the number of mitered pieces based on the velocity (#1) in the ductwork. Unless the specifications call for something different or other limitations are stated, then this SMACNA table can be safely used to figure the quantity of miters (#3) to add to 90, 60 and 45 degree round elbows.
As can be seen from Table 3-1 as the velocity increases (#1) within the elbow, the greater the quantity of miters (#3), and the larger the Centerline Radius (#2) is required. The centerline radius makes the elbow take a wider turn, which allows for better aerodynamics and performance.
SMACNA Table 3-1 Mitered Elbows
Machine Made Gored Elbows
Watch the enclosed video to see how a version of the gored elbow can be made quickly in this sheet metal fabrication shop.
Making Sheet Metal Elbows
Adjustable Elbows
The most common 45 and 90 degree elbows are fabricated to have adjustable gores, so that you can spin the gores and make various angles out of the two types.
Spot Welded Elbows
For system and designs requiring a better fitting, you might find the requirement that the gores be SPOT WELDED. Every so often around the circumference of the seam a spot weld will be made to hold the two segments of the fitting together, giving it a stronger bind then that used for an adjustable elbow.
Continuously Welded Elbows
And for systems requiring a tight seal there are fully welded fittings with a continuous weld as opposed to a spot weld every so often around its circumference. This type of fitting will have a continuous weld at the seams and joints.
The cost of the fittings is usually related to the method of fabrication with adjustable type fittings being the least costly, then spot welded, and fully welded being the most expensive fitting type. Having to fully weld the seams of a fitting requires more shop labor and the use of a heavier gauge to allow for a clean weld without destroying the metal, this is why it is the most expensive type of seam and joint for a round fitting. There are other types of elbows used through-out the industry such as;
Stamped Elbows
This elbow is created from two pieces that were stamped out. This requires that the two half sections be welded together along there longitudinal seam with either a continuous weld or spot weld.
Pleated Elbows
Just as the name implies this elbow has a pleated appearance, almost appearing as if it was a piece of flex duct bent in the shape of a 90 degree elbow and then harden. I have personally never used this type of fitting, but just wanted to make you aware of the terminology in case you live in an area where they are used.
Standing Seam Elbows
This fitting is fabricated with segmented pieces with standing seams that lock to an adjoining segment.
Standing Seams
Oval Duct and Fittings
Not as commonly specified as round duct, but it has its application. Oval duct is made from a section of round spiral duct, that is ovalized, or stretched into an oval size. See the enclosed video to see this machine in operation.
Flat Oval Spiral Duct
Watch the below video to see the installation of oval duct and fittings. Notice that the reducer being used is undersized on its collar allowing the oval duct to slip over the collar. They are using Unistrut with threaded rods as hangers for the ductwork.
Oval Ductwork
Round Industrial Classifications
This course doesn’t cover Industrial Construction standards, but you should be aware that duct is classified by the medium that is traveling through the ductwork.
Round Industrial Standards will cover round ducts that carry corrosive fumes or particulate matter, like that found in a dust collection system or industrial processes. The non-industrial standards cover ducts from +10” wg (2,500 Pa) to -10” wg, while the industrial standards cover ducts up to a negative -30 wg.
Class 1 – Includes non-abrasive applications: Makeup Air, General Ventilation, Gaseous Emission Control
Class 2 – Includes applications with Moderately Abrasive Material in Low Concentration: i.e., buffing and polishing woodworking, grain dust, etc.
Class 3 – Includes applications with Highly Abrasive Material in Low Concentration: i.e., abrasive cleaning operations, dryers, kilns, boiler breaching and sand handling, etc.
Class 4 – Includes applications with Highly Abrasive particulate in High Concentrations; i.e., materials conveying high concentrations of particulate in all examples listed under class 3 (usually used in heavy industrial plants such as steel mills, foundries, mining and smelting).
Shop drawings should be created by someone in the company familiar with detailing. Detailing is the process of taking the engineered set of drawings and converting them into shop drawings that the field will use to install the sheet metal.
Sheet Metal Detailer
The sheet metal detailer’s job is to coordinate the layout of the ductwork with all other trades in order to avoid collisions or conflicts. This position is held by a union member for companies that are signatory to a local Sheet Metal Union. Their job is to ensure that the sheet metal fits within the space and to show all the required dimensions on the drawing so as to make the field installation go smoothly and without wasting ductwork and fittings because they don’t fit into the space shown on the drawings.
BIM Detailing
The shop drawings will show the ductwork exactly where it needs to be installed in order to avoid building components and other trades.
The sheet metal detailer will review the architectural, structural, electrical, plumbing and other trade drawings in an effort to avoid installing ductwork where these trades have their systems and where structural supports and architectural items are to be installed.
Set of Drawings
Detailed Shop Drawings
Looking at the sheet metal shop drawing below you can see that additional items are shown on these drawings compared to the engineered set. These drawings are drawn in CAD (Computerized Aided Drawings), which is drawn on a special computer program. If you have a small project then using CAD may not be feasible, and in this cases the detailer will just fill out the sheet metal fabrication shops order forms directly from the engineered set of drawings and from what is discovered during a site visit for existing buildings.
Sheet Metal Shop Drawings
The numbers in the red circles correspond to the following;
#1 (Duct Size & Joint Length) This shows that the rectangular duct that is 70” x 18” in size is 56 1/4” in length. This duct is made from a 5 foot (60 inch) coil width, and the difference is from the joint. 60” coil width – 3 3/4” joint (1-5/8” each joint) = 56 1/4” in length.
#2 (Plenum Size & Length) This is the plenum off of the VAV box, which is a duct that is 20” x 17-1/2” in size by 36” in length.
#3 (Duct Elevation) This shows the bottom and top elevation of the ductwork. This shows that the bottom of the duct is 9’-11” off of the floor, and that the top of the duct is at 11’-5” off of the floor.
Shop Drawing Elevation
#4 (Service Access) – According to the manufacture or local code authority, each piece of equipment, valve or accessory that needs adjustment or service is required to have an unobstructed access area. As shown in item #4 the hatched area next to the VAV boxes must be kept clear so that a service technician can access the controller.
#5 (Ceiling Height ) – The height of the ceiling is indicated to be 8’-2”
Sheet Metal Shop Drawing
#6 (Benchmark Distance) – The location of the edge of the ductwork is indicated as being 10’-0” from the column line.
#7 (Wall Opening) – Top and Bottom elevation of Return Air Boot opening in Fire-Rated Wall, as can be seen by the Fire/Smoke Damper.
#8 (Direction) – BF = Bottom Flat. This is a transition fitting that is changing the size of its depth. In order to inform the fabrication shop and the field installer which side remains flat these acronyms are used. It’s also possible to install a concentric transition, where both sides converge evenly.
#9 (Duct Offset) – This indicates that the duct needs to drop by 16” in order to get under the large main supply air duct. It’s important to remember this when you are working with a set of engineered plans that haven’t been detailed into shop drawings. Remember to add extra fittings when crossing ducts.
#10 (External Insulation Wrap) – The dotted line on the outside of the duct indicates that this ductwork will get wrapped with insulation, most likely by your insulation subcontractor.
#11 (Internal Liner) – These dotted lines on the inside of the duct indicate that the ductwork is lined with acoustical liner.
From Shop Drawing to Fabrication Equipment
From the shop drawings the detailer will either draw the required duct and fittings onto an order form or the CAD software will download the information to the shop fabrication equipment with or without the shop superintendent’s modifications.
Sheet Metal Shop Order Form
For those that have an integrated software system where the CAD drawings can be directly sent to the fabrication equipment, this will save a lot of time by not having to draw out each piece required to be fabricated or enter data into the coil line or plasma cutter.
Detailing for Retrofit Projects
Detailing for existing buildings can be done in a similar manner as that of new construction, except that you will need to do a site survey to document what is in the space where new sheet metal or HVAC equipment will need to be installed. Again, based on the size of the project and the requirements of the RFP (Request for Proposal) the use of CAD may or may not be used.
For small retrofit projects the detailer will visit the project site and make the measurements required to get the needed ductwork and fittings fabricated. There is no need to go through the expense of drawing everything in CAD.
Control / Reference Point
The construction project will have one or more control points from which everything can be measured from in order to ensure the accurate location of walls and other trades. The control point is determined by a field engineer and has an X, Y, Z reference point.
Detailing Reference Lines
Navisworks by Autodesk (Collision Detection)
Most large new construction projects are built within some form of modeling software like Autodesk Revit, Bentley or many others.
In the enclosed video at about the three minute mark you will see that the Navisworks software will pick up a collision between a sheet metal duct and a structural beam. Navisworks combines the different designs from the various trades (Architectural, Structural, HVAC, Electrical & Plumbing) and combines them together, and then searches for clashes that occur between them. Clashes occur when two different designers are trying to occupy the same space in the building, like the duct that is placed where a structural beam is located.
Using Autodesk Navisworks helps eliminate change orders and costly field errors by finding them before they get installed.
AutoDesk Navisworks
Shop drawings are done in AutoCAD, Autodesk Revit MEP or some other modeling software that allows for the coordination with other trades using Navisworks to ensure that the sheet metal will fit within the building without hitting anything.
Revit
BIM (Building Information Modeling)
The use of BIM is widely used throughout the industry for commercial contractors doing new construction projects. Often the requirement to use BIM is specified in the design criteria for many Federal, State and local Municipalities in addition to the private sector. BIM make coordination easier and reduces the amount of change orders due to the collision checking before construction begins.
BIM – Building Information Modeling
The sheet metal estimator will need to provide hours in the estimate to cover the detailing requirements per the RFP (Request for Proposal) or ITB (Invitation to Bid). If there are no requirements then your companies minimum level of detailing required to accomplish the ordering of ductwork and fittings.
Companies that maintain historical data from completed project will be able to look at metrics from those projects which could help determine the hours required for the current project. A metric like, percentage of detailing hours to total field hours would be helpful.
10% Detailing (historical data feedback)
Example: Current Project has 2,000 field labor hours.
Calculate detailing: 2,000 Field Hrs x 10% = 200 detailing hours
Below is a screen shot of a small section of the Sheet Metal Material & Labor Summary tab of the MEP Academy Estimating spreadsheet that allows you to enter a percentage of your total field labor for detailing.
Detailing Option on MEP Academy Estimating Spreadsheet
Summary
The detailer will create shop drawings by reviewing the location of all the architectural, structural, electrical and plumbing elements in addition to the various other trades that require space within the building for their component.
The detailer will coordinate with the other trades to ensure that everything fits within the space allotted. It’s possible that software like Navisworks will be used to detect collisions automatically within the software program, thereby minimizes field change orders.
Detailing can be done on a computer using some form of CAD, or on smaller project detailing can be done by hand and drawn out on an order form.
Detailed drawings (shop drawings) shows the size, length and duct joint information for each piece of ductwork and fittings, along with their elevation height.
