Download the PDF Takeoff form or use your own tablet or computer to record your answers that match the list from 1 to 13 for the duct or fittings that are shown on the image below. Write down a description of the duct or fitting along with the appropriate size if shown. Don’t worry about the length of ducts in this exercise. After you have completed your takeoff, check your answers with the online answer sheet.
Rectangular Sheet Metal Practice Test
Fill out the following chart with your answers that match the above image.
VAV High-Side Rectangular Ductwork – Practice Test #2
VAV High Side Rectangular Ductwork #2
Review the image below and see if you can fill out the takeoff sheet with the numbers that correspond to the rectangular duct or fittings.
VAV High-Side Rectangular Ductwork #2VAV High-Side Rectangular Ductwork #2 – Practice Test #2
VAV Low & High Side Takeoff
Download the PDF Takeoff form or use your own tablet or computer to record your answers that match the list from 1 to 36 for the duct or fittings that are shown on the image below. Write down a description of the duct or fitting along with the appropriate size if shown. Don’t worry about the length of ducts in this exercise. This is again practice to see if you can correctly identify all the duct and fittings by their correct names.
VAV Low & High Side Takeoff Practice TestVAV Low & High Side Ductwork Practice Test #2
Fill out the list below from 1 to 30 that corresponds to the numbers on the below image, and then write down a description of the duct or fitting along with the appropriate size if shown. See if you can get 100% of the pieces correct. After you have completed your takeoff, check your answers with the online answer sheet. You can also download the PDF Takeoff Form here.
VAV Sheet Metal Practice Test 1
Fill in Table below with answers to VAV Low Pressure Ductwork Image Above. Don’t include any Air Distribution Grilles, just ductwork, fittings and duct accessories.
You can also download a PDF version of the takeoff sheet here.
Sheet Metal Practice Test #1 – Blank Form
Below is a copy of the answer sheet for Practice Test #1 and the following test.
Low Pressure Supply – Option #1
Below is another round supply duct practice takeoff for you to get comfortable recognizing how different engineers represent the various fittings that are not defined. There are several options available to you with this takeoff depending on what the engineer allows in the specifications. We will provide several optional answers. Don’t worry about the lengths of ducts, just indicate that there is a section of duct required.
Round Sheet Metal Takeoff Practice Test
Fill in table below for each of the numbered items shown in this image along with the description of the duct or fitting along with its size. Don’t worry about the lengths of duct at this time, just indicate if it’s a section of duct or the type of fitting.
After completing the sheet metal takeoff check your answers online with the corresponding answer sheet for this practice test.
Sheet Metal – Low Pressure Supply Test Option 1
We didn’t ask you to finish all the individual branches, but in this case there would be short stubs of 10” duct to each linear diffuser. What is missing from this engineered drawing is the volume damper for each linear diffuser but don’t worry about that now, just remember to add one in a real estimate as they are required to balance the air to each linear diffuser.
Low Pressure Supply – Option 2
We added an optional method of estimating the previous image as shown below with our modifications. Fittings #6, #8 and #10 will be eliminated and #16 will be added in their place, including item #17. Can you identify the newly added fittings #16 & 17?
Sheet Metal – Low Pressure Supply – Option 2Sheet Metal – Low Pressure Supply Duct – Option #2
If you have a computer estimating program with the capability of onscreen take-off, then this course will give you a good understanding of what is required in order to understand the parts and pieces that go into a computer estimating system.
Being able to do a take-off by hand will give you a better understanding of all that goes into the automation of a computer program. Having a computer estimating program is required for any company wanting to bid plan and specification projects as opposed to a retrofit job.
Computer estimating speeds up computation and provides a faster method for doing take-offs and updating prices and a host of other advantages. The following process and procedures for doing a take-off is described from the point of doing a manual non-computerized take-off, but is applicable to understanding what goes into an estimating software program.
Sheet Metal Takeoff
We will cover the steps needed in order to do an accurate and thorough takeoff of the sheet metal. Now that you have learned how to recognize round and rectangular ductwork, fittings and specialties, we will learn a few variations or options you might have if the drawings and specification are not clear on which type of fitting to use.
It is best to always start at the source of the air, such as the air conditioner or fan and work your way to the last air outlet or inlet grille. In the case of a VAV system with high side and low side ductwork you can begin at the shaft where the main ductwork comes from the air handler as shown below, or if floor mounted Air Handlers are used, you can start in the mechanical room with the sheet metal connection to the Air handler
Choosing your Fittings and Branch Connection
What are your choices when you arrive at a branch that is perpendicular to the main run? The most aerodynamically efficient fitting choice is shown below which includes two transitions and a 90-degree elbow, note that a radius elbow could also be used. This is also the most costly choice, because of the number of fittings that has to be fabricated in the shop. There are 3 fittings to fabricate (2) transitions & (1) 90-degree elbow.
Duct Split-Option
Another less costly alternative as shown below would be to provide one branch to continue forward, and the other would have a 90 radius elbow. Obviously this alternative has fewer fittings and as such will be less labor intensive, and less expensive to fabricate.
The assumption in the arrangement below is that the small duct that continues straight ahead will have the same depth as the main because no transition is indicated to change size. They both accomplish the same thing, but with different approaches. There is only one fitting; (1) 90-degree radius elbow, as opposed to three fittings in the above scenario.
90-Degree Radius Elbow
Assuming that the duct size would need to be reduced according to the duct sizing requirements, then a transition after the branch tap would be needed to resize the duct for the remaining CFM (cubic feet per minute).
The third option below uses a 45-degree tap-in fitting for the branch connection, and a transition for the straight run. In this arrangement there are only two shop fabricated fittings; (1) transition and (1) 45-degree tap.
45-Degree Tap Branch Connection
If the plans and specifications don’t indicate which method is the preferred or required, then it becomes a company decision, based on your company’s construction standards. If the engineer doesn’t limit your choice of fittings, then you have to make the decision as to which fittings to use in the above scenarios.
You can go with the least expensive option or the most energy efficient which is the more costly alternative. Make sure to read the specifications and look for any drawing details that show how you must make sheet metal branch connections.
Duct Offsets Up or Down
The symbol below indicates that the duct is rising up or down in the direction of the arrow. Ducts that indicate they’re going up (UP) will increase their bottom elevation, while ducts that indicate they’re going down (DN) will decrease the bottom elevation of the duct.
Duct Offsets
VAV / CAV Terminal Box Connection
When contracting commercial construction projects it is common to find some form of Terminal box controlling air volume into the space. These VAV (Variable Air Volume) or CAV (Constant Air Volume) terminals will have a piece of duct coming off the front, or a Manufacture/Contractor provided lined plenum. This connection to the terminal box is often defined by the engineer or shown on the detail page of the design drawings. There are several choices shown below.
VAV / CAV Plenum
Often the engineer will require a lined plenum be attached to the VAV box. This helps with sound attenuation. It’s also possible that no taps or connections will be allowed on the sides of the plenum, and that you would need to make all connections after the plenum. The plenum is shown in blue below.
VAV / CAV with Lined Plenum
VAV /CAV Square to Round
One of the most economical ways of connecting to a VAV terminal is to immediately start with a Square to Round fitting. This is because most contractors find it less expensive to purchase and install round duct as compared to rectangular, so they want to transition immediately.
VAV / CAV with Square to Round Fitting
Rectangular Duct Takeoff
The best way to learn how to do a sheet metal take off is to jump in and try for yourself. But before you do, we’ll show you several audit trails of sample takeoffs. Just follow the number sequence of the audit trail and see if you can identify the duct, fittings or accessories as we have shown them below starting with number 1.
That was pretty simple as each piece didn’t need much interpretation because of their easily recognizable shape and symbol. It gets a little more difficult as we go along and the experience of a trained eye will pick up the items that aren’t shown but required.
Rooftop Packaged Unit – Down Shot with Supply Ductwork Shown Highlighted
Audit Trail #2 (Packaged A/C Unit on Roof)
Equipment Flex Conn. 26” x 24”
Riser Duct 26” x 24”
Elbow – 90 Degree 26” x 24”
Duct 26” x 24”
Elbow – 90 Degree 26” x 24”
Duct Section 26” x 24”
Transition 26” x 24” to 20” x 16”
Duct Section 20” x 16”
Elbow – 90 Degree 20” x 16”
Duct Section 20” x 16”
Transition 20” x 16” to 14” x 8”
Duct Section 14” x 8”
End Cap 14” x 8”
Rectangular Tap 18” x 16”
Duct Section 18” x 16”
The audit trail starts with the vertical connection to the Air Conditioner using a (#1) Equipment Flexible Connector, then (#2) Riser Duct Section, followed by a 90-degree elbow or an end cap to form a plenum. There is a good chance that you might have a transition from the size of the connection at the equipment to the size that you want to run the main duct size.
Often the engineer won’t provide an elevation view that shows how far the duct drops vertically from the Air Conditioner or Air Handler above, so you’ll need to estimate the approximate vertical distance based on the floor to floor height and the ceiling height in that area. Items #1 and #2 above aren’t shown on the drawings but are inferred by the drawings and notes.
Multi-Zone Units
A Multi-Zone Unit (#1) has multiple supply air ducts coming off the unit feeding individual zones. Instead of one main supply air duct coming off the AC unit, these units have multiple supply air ducts. As can be seen in the drawing below, the first item of sheet metal attached to this multi-zone unit is the flexible duct connectors. You would start with the first zone and then continue until you completed each of the zones on this unit.
Most of what you will find on each of these sheet metal duct runs is a Flexible connector at the unit, straight duct sections, angles, transitions, Reheat coils (#3), Volume Control Dampers and 90-degree elbows (#4).
This Multi-Zone Unit (#1) provides 100% Outside Air through a Louver and OSA Plenum (#2) at the exterior wall. Its normal for units to sit on a concrete housekeeping pad (#6). The Multi-Zone unit is fed with CHW (Chilled Water) & HHW (Heating Hot Water) piping (#5).
Multi-Zone Unit with Sheet Metal shown in light grey
This particular multi-zone air handler is for a hospital so it has 100% outside air and NO return air. The outside air can be seen rising off the top of the back portion of the multi-zone unit and then turning with the use of a 90-degree elbow where it then taps into the back of a plenum attached to an Outside Air Louver.
Double Duct System
The Double Duct System is another variation of duct configurations you will see when bidding on commercial projects. This system uses two mains supply air ducts, one for the cold air and another for the heated air. As shown in the image below the system uses double-duct mixing boxes (#1) which is fed by a main COLD Supply (#2) and HOT Supply (#3) duct main, to control the temperature set point.
Double-Duct System
With this system you’ll want to separate the high side from the low side ductwork. The demarcation or separation between the high and low side is determined by the location of the double duct mixing box. Everything before the box is considered the high side; this would include the main cooling and heating supply air mains that feed each mixing box. Everything after the box is considered the low side; this would include the flexible duct connectors to the air distribution diffusers.
Did you find the (6) 90-Degree Elbows for item “F” in the image above? If not, look again and then check the image at the end of this course for the actual count.
The reason to keep the various high and low pressures duct takeoff’s separate is twofold, first the pressure classification or static pressure at which the duct will be fabricated differs, and secondly, the labor for the different duct systems will be different, as the main ducts and fittings are larger, while the low side ductwork is much smaller.
VAV high Side Ductwork & Page Break
When floor plates or the size of a building floor plan is too large to fit on a single page the engineer will show a Match Line (#1) where you can conveniently stop your takeoff on one page and begin on another. The dotted line (#1) running horizontally across the page in the below image matches with the dotted match line (#5) shown on the other drawing below.
Match line between drawings
Your takeoff for this drawing should start and stop at this match line or a significant break point such as the SFD (Smoke Fire Damper) (#4) so that you don’t accidentally double up on your takeoff. This is a VAV system with both the High and Low Supply Air portions shown. This is where you will keep the two separate when you do your takeoff. In the image above you will NOT takeoff anything in the hatched out area (#2), or (#6) below as they belong to the other drawing. Item (#3) above and (#7) below are the direction in which your takeoff will proceed.
Match Line – Matching Other Section
You can see that the match line of the second drawing above matches that of the first one except for the direction in which the new work is shown.
Mechanical Rooms and Elevation/Section Views
It is often difficult to distinguish what fittings or lengths of ducts are required in mechanical rooms and crowded areas. Without an elevation/section view you would need to make an educated guess about vertical distances and fittings, especially if there were no Architectural plans to inform you of the heights and restrictive building elements.
Plan View of a Mechanical Room
The plan view of the Supply (#2), Return (#3) and Exhaust (#4) systems show that the ductwork rises from the equipment, but there is no way to tell how much straight duct there is on the riser without a section view (shown below). Looking at the section view below you can measure the distance with your computer program or use a scale to get the exact length because it is drawn to a 1/4”= 1’-0” scale. Without an elevation view you would have to make an educated guess as to how much of a vertical rise the duct makes.
Elevation View of Mechanical Room above
If you have submittals (Physical & Dimensional data) of the Air Handler (#1) and exhaust Fan (#4) and the Architectural drawings, than you can determine an approximate height that will be good enough for estimating purposes. As you can see in this elevation view there isn’t that much of a vertical rise in any of the three systems. The Return Air (#3) and Supply Air (#2) ductwork have short stubs of duct before they turn using an elbow.
Answer to Double-Duct Question above
Answer to Question above on Double Duct Systems
There are six elbows. There is one elbow (#1) after the starting collar coming off the main duct, then the 6” duct turns vertically down (#2) and then turns again (#3) immediately turning horizontally into the double duct mixing box. There are three elbows on one main branch connection from the Main Heating Duct to each Double-Duct box, the other main branch goes straight into the box from the side of the Main Cold Duct without any elbows.
We’re going to cover how to Calculate GPM of a new Chiller Evaporator or Condenser Coil or any New Coil or Heat Exchanger by a field measurement of the pressure drop compared to the rated pressure drop of the equipment.
If you prefer to watch a video on this topic, scroll to the bottom of this page for link.
In this equation GPM2 is the actual flow rate that we’re going to calculate, it could be for any coil whether in a chiller, fan coil or heat exchanger.
How to Calculate Flow (GPM) in a Coil
So the Rated GPM is GPM1, times the square root of PD2, which is the actual pressure drop that we are going to measure. This is different than the Rated Pressure drop, which is PD1, the pressure drop across the Chiller’s Evaporator, Condenser or Heat Exchanger that your trying to measure.
So what will happen to the GPM if the Pressure Drop (PD) increases or decreases?
For our example we’re going to take a new chiller that was Rated for 600 GPM at 14 feet of Pressure drop through the Evaporator.
Measuring Flow Across a Coil
When we go into the field and measure the actual pressure drop we get 13 Feet.
Field Measurement Confirming an Actual Pressure Drop of 13′ vs the Rated Value of 14′
Now what we are going to do is we’re going to take all the known Rated conditions of the new piece of equipment, in this example the evaporator of a chiller and the actual measured pressure drop from our field technician.
So here is our formula. All we’re going to do is put in the known Rated values for the evaporator. Which GPM1, the Rated GPM is 600, times the square root of the actual measured pressure drop, which came out to 13 feet divided by the rated pressure drop (PD) of 14 feet for our example evaporator.
All it is at this point is math. So, doing the math we come up to 578. So our 600 GPM at 14 feet pressure drop Rated condition is now only flowing 578 GPM due to the decrease in pressure drop.
How to Calculate Pressure Drop in a Chiller or Coil
So a decrease in pressure equals a decrease in GPM.
