HVAC Takeoff Guide

An HVAC takeoff is a count of every piece of equipment and air device on the job plus a measurement of every foot of duct, converted into the units the work is actually bought and built in. You do it in four passes: pull the equipment count off the mechanical equipment schedule, pull the air device count off the air device schedule, measure the duct run by run segregated by system, size, gauge and material, then derive the accessories that fall out of those numbers. The measurement work ends with one conversion that separates HVAC from every other trade: linear feet becomes square feet of sheet metal, and square feet becomes pounds.

That conversion is simple arithmetic and it is worth memorizing right now. For rectangular duct, surface area in square feet per linear foot equals the width plus the depth in inches divided by six. A 30 by 12 duct is (30 + 12) / 6 = 7.00 square feet for every foot of length. Multiply square feet by the weight of the gauge and you have pounds. Twenty-two gauge galvanized is 1.406 pounds per square foot, so that same 30 by 12 duct in 22 gauge weighs 7.00 x 1.406 = 9.84 pounds per foot. Those two steps are the whole engine. Everything else in this guide is about doing them without lying to yourself.

Why Pounds

Pounds is not estimator vanity. It is the unit the industry runs on. SMACNA publishes its Reference Manual for Labor Units in pounds per hour and hours per piece, and those tables were originally assembled from a survey of more than 300 member firms across the United States and Canada. Shops buy coil and sheet by weight. When a commercial mechanical estimator says a job is "eleven thousand pounds," every other person in the conversation knows roughly what that means in trucks, in shop days and in crew size.

Residential and light commercial contractors often work in different units entirely, and that is legitimate. In a long-running thread on HVAC-Talk about pricing sheet metal, one estimator laid out exactly how the split works in practice: he priced round on a per outlet basis, rectangular at a set price per four foot section installed, and saved the price per pound of metal for bigger commercial work. A general contractor in the same thread just wanted a dollars per square foot of house number for custom homes. All three are real methods. They fail in different places, and knowing which one you are using matters more than which one you picked.

The Word Means Two Things

Before you go further, clear up the vocabulary, because it trips up searches and it trips up subs. In HVAC, "takeoff" means two unrelated things. It is the estimate, which is what this guide is about. It is also a physical fitting: the spin-in collar or branch takeoff that taps a runout off a trunk or plenum. If someone on the phone says the takeoffs are too close to the end cap, they are not reviewing your bid. ACCA Manual D is explicit on the fitting version, page 30: the closing plate at the end of a trunk creates a turbulent zone, and the centerline of a branch takeoff has to sit at least 18 inches upstream of a trunk end plate or a trunk reducing fitting. Useful to know, and unrelated to your spreadsheet.

The Order of Operations

Take the job off in this sequence, because it stacks the risk correctly:

1. Equipment. Read the mechanical equipment schedule, count units by tag, and note anything that drags other scope with it (curbs, rails, isolation, condensate, electrical disconnects that may or may not be yours).

2. Air devices. Count diffusers, registers and grilles off the air device schedule against the reflected ceiling plan. Verify the plan matches the schedule, because they disagree more often than anyone admits.

3. Duct. Measure run by run, keeping system, pressure class, size, gauge and material separated. Never merge supply, return, exhaust and outside air into one line.

4. Accessories and derived quantities. Hangers, volume dampers, fire and smoke dampers, access doors, turning vanes, flex connections, sealant, insulation, liner. Most of these are functions of the numbers you just produced.

Then convert, add your scrap allowance, and price. Price is the last thing that happens, not the first.

Every line on an HVAC takeoff belongs to one of three families, and they behave so differently that mixing them on one sheet is the fastest way to lose a job. Keep them physically separate.

Family One: Counted, High Dollar, Low Risk

Equipment. Rooftop units, air handlers, split systems, fan coils, VAV boxes, exhaust fans, furnaces, condensers, energy recovery units, unit heaters. These carry the largest single dollar amounts on most jobs and they are the easiest quantities to get right, because they are enumerated on a schedule with tags. If the schedule says RTU-1 and RTU-2, there are two rooftop units. You are not measuring anything.

The risk here is not miscounting. It is missing the tail that comes attached. A rooftop unit is never just a rooftop unit. It is a unit, a curb, curb adapter or rails if it is a changeout, flashing, vibration isolation, a flex duct connection at the supply and return, condensate piping and trap, a service disconnect, and often a crane pick. Every one of those is a separate material line and several of them live on somebody else's drawing.

Family Two: Counted, Many, Medium Risk

Air devices and in-line accessories. Supply diffusers, return and exhaust grilles, registers, volume dampers, fire dampers, smoke dampers, access doors, turning vanes, spin-in takeoffs with damper, flex connections. These are also counted rather than measured, but there are a lot of them and they are scattered across several sheets.

Air devices come off the air device schedule cross-checked against the reflected ceiling plan. Do the cross-check every time. The schedule tells you the type, neck size, face size, finish and CFM for each tag. The ceiling plan tells you how many of each tag actually landed. When an architect moves a ceiling grid late, the plan changes and the schedule sometimes does not.

Dampers are worse, because many of them are not drawn as an object at all. Fire and smoke dampers are required by where a duct crosses a rated assembly, which means the quantity is determined by the life safety plan and the wall types, not by the mechanical sheet. You find them by tracing every duct penetration against the rated wall and shaft locations. That pass is tedious and it is not optional.

Family Three: Measured, Then Converted Twice, Highest Risk

Duct. This is where the money leaks, and it leaks for two separate reasons.

The first reason is the same one that hurts every trade: a floor plan is a horizontal projection. Risers, drops from a trunk down to a ceiling diffuser, the vertical leg from a rooftop unit down through the roof curb into the building, and every offset around a beam are all real metal that a flat plan trace values at zero or close to it. Section views and mechanical riser diagrams carry those feet. Read them.

The second reason is specific to sheet metal and it is the harder one: the quantity you measure is not the quantity you buy. You measure linear feet. You buy and fabricate in pounds. Getting from one to the other requires the gauge, and as the next two sections show, the gauge is frequently not on your drawings in any usable form.

Keep the Systems Apart

Inside the duct family, segregate by system before you segregate by anything else:

• -Supply, by pressure class, because pressure class drives gauge and joint type
• -Return, noting that return duct on the suction side of a fan is negative pressure service and SMACNA treats positive and negative pressure separately in its construction tables
• -Exhaust, which may be a different material entirely if it is grease, fume or dishwasher exhaust
• -Outside air, which usually needs insulation the rest of the supply does not
• -Relief and transfer, which are easy to skip because they are short

A schedule that assigns one pressure class to a whole project is a common specification error rather than a real design, and it is worth an RFI. Different zones operate at different pressures. If a spec sheet gives you a single class for everything from a short transfer duct to the main trunk off the air handler, somebody set a default, and you are being asked to price the heaviest interpretation of it.

This is the chain. It is three steps and each one is exact.

Step One: Linear Feet, by Size

Measure every straight run at its scale length, segregated by size. The output of this step is a list that reads like "30x12, 60 LF" and nothing more. Do not average sizes together, do not round a 30 by 14 into the 30 by 12 line to save time. Size is the multiplier in step two, so blending sizes propagates straight into pounds.

Fittings are counted as pieces at this stage, not measured as length. An elbow, a transition, an offset, a tee and an end cap each get tallied by size and type. You will convert them separately, because a fitting consumes considerably more metal than its centerline length suggests and its labor bears no relationship to a foot of straight duct.

Step Two: Square Feet of Sheet Metal

For rectangular duct, the surface area of the four sides per linear foot is the perimeter in feet:

SF per LF = 2 x (W + H) / 12 = (W + H) / 6, with W and H in inches.

That is not a rule of thumb. SMACNA publishes the matrix version of it in Appendix A-7 of the HVAC Duct Construction Standards as a width by depth lookup, and the table reproduces the formula exactly at every entry: 12 by 12 reads 4.00, 30 by 30 reads 10.00, 30 by 108 reads 23.00. You do not need the table. You need to divide by six.

For round duct, surface area per linear foot is the circumference in feet:

SF per LF = pi x D / 12, with D in inches. A 12 inch round duct is 3.14 square feet per foot.

Step Three: Pounds

Multiply square feet by the weight of the gauge. These are the nominal galvanized sheet weights from SMACNA Appendix A-2, and they are the seven numbers that matter:

Put the chain together on one duct. A 24 by 12 trunk, 40 feet long, in 22 gauge:

• -(24 + 12) / 6 = 6.00 SF per LF
• -6.00 x 40 = 240 square feet
• -240 x 1.406 = 337.4 pounds

Run that on every line of your size list and total the pounds column. That total is the number your shop, your labor tables and your material buyout all want.

(Pulling the linear feet off the sheet size by size is the mechanical half of this, and it is the part Tectonic automates. It reads the runs off the PDF and returns the quantities with materials and your markup priced out. Work a full duct schedule by hand at least once anyway, because the conversion to pounds is exactly where a tool can be confidently wrong, and you want to know what right looks like before you trust anything.)

Round Duct and the Seam Allowance

Run the same chain on round duct and compare it against SMACNA Appendix A-10, which lists approximate round duct weights in pounds per lineal foot for both spiral and longitudinal seam construction. A 12 inch round in 24 gauge calculates to 3.14 x 1.156 = 3.63 pounds per foot. SMACNA lists it at about 3.78. The published figure runs a few percent above the bare geometric number because the seam laps consume metal that a circumference calculation cannot see.

That gap is a useful reminder about the whole method. Geometry gives you the metal in the walls. It does not give you the metal in the seams, the laps, the flanges, the reinforcement angles or the drop left on the shop floor. Those are real and they are additive.

Scrap and Drop

Sheet metal is cut from coil and sheet, and what does not become duct becomes scrap. Most shops carry something in the neighborhood of ten to fifteen percent for scrap and drop, and the right number is a property of your shop, your coil widths and your fitting mix, not of the industry. If you have any fabrication history at all, compute it: pounds purchased divided by pounds installed, over a year. Use that. If you have no history, use the middle of the range and start keeping the data this quarter.

Why Round Versus Rectangular Changes the Whole Number

Because the takeoff converts to weight, a material substitution moves your number hard. Writing in SNIPS on spiral versus rectangular duct, Peeter Vesik of SPIDA put the comparison in estimating terms: a round or flat oval spiral system can run up to 40 percent less in weight than the rectangular equivalent, and installed cost up to 50 percent less overall. The geometry driving it is easy to check yourself. A 12 by 12 rectangular duct has a 48 inch perimeter. Its equivalent diameter round is 13.1 inches, a perimeter of about 41 inches, roughly a 15 percent reduction in surface area for the same air. Less surface is less metal, less sealant and less insulation.

He also noted the seam and leakage side: rectangular duct carries two longitudinal lock seams for its full length plus a transverse slip connection every four to five feet, has traditionally been hard to hold under 10 percent leakage and gets to 3 or 4 percent with better connections, while spiral seam duct lands in the 1 to 2 percent range. If your per pound rates were built on rectangular jobs, do not carry them onto a spiral job unexamined.

Here is the part that separates estimators who have read the standard from estimators who have read blog posts about the standard.

Search for HVAC duct gauge and you will find a dozen clean tables presenting gauge as a lookup: find your pressure class, find your duct width, read off the gauge. Those tables are a simplification, and if you build a pounds-based estimate on them you will be wrong in a direction you cannot predict.

What SMACNA Actually Says

Gauge is not determined by width and pressure class. It is traded off against reinforcement spacing. The standard's own worked examples make this unambiguous. For a 30 by 18 duct, the choices SMACNA lists for the 30 inch side are 16 gauge unreinforced, or E class reinforcement on 22 gauge at 10 foot spacing, or D on 24 gauge at 8 feet, or D on 26 gauge at 6 feet, or C at 4 feet. For a 72 by 72 duct at 5 foot joint spacing with no intermediate reinforcing, the options include 18 gauge with H rated joints, G rated joints with tie rods added, or 24 gauge at two and a half foot spacing with F ratings.

Read that again in estimating terms. The same duct, on the same drawing, at the same pressure class, has three or four legal constructions with materially different weights. Twenty-six gauge at 0.906 pounds per square foot against 16 gauge at 2.656 is a factor of nearly three on the sheet metal, partly offset by reinforcement steel that the lighter option requires and the heavier one does not.

There is a second trap in the same neighborhood. When a flange is rolled on the end of a duct section, the minimum gauge in the joint rating table can override a lighter duct wall gauge that the reinforcement spacing tables would otherwise allow. The wall goes up to satisfy the joint. So even reading the tables correctly, the governing gauge sometimes comes from the connector rather than the panel.

What This Means For Your Takeoff

It means a pounds number is a statement about a fabrication method, not a measurement of a building. Two competent shops bidding the same set legitimately produce different weights.

So do this:

• -Get your shop standards in writing and use them. SMACNA's appendix includes a blank form for shop standards and a contractor's analysis worksheet for exactly this reason. A shop standard is a decision, made once, about which gauge and reinforcement combination you build at each size and pressure class. Once it exists, your takeoff is deterministic.
• -If you are bidding as a mechanical contractor to a sheet metal sub, take off linear feet by size and let them convert. You are not the one who gets to pick the construction.
• -Never accept a gauge from a takeoff tool without knowing where it came from. If software hands you pounds, ask what gauge table it applied and whether it matches your shop. The linear feet are objective. The pounds are an assumption with a number attached.
• -Flag single pressure class schedules. If the whole project is marked 2 inch water gauge, part of that is a default rather than a design, and you are pricing heavier construction than the job needs.

Residential Is a Different Rulebook Entirely

If you are doing houses, the commercial gauge discussion largely does not apply to you. The 2024 International Mechanical Code, section 603.4, requires metallic duct to be built to SMACNA, but carries an explicit exception: duct installed within single dwelling units may instead use the minimum thicknesses in IMC Table 603.4. That table is much lighter. Round galvanized duct under 12 inches diameter at half inch water gauge needs 0.013 inch material, which is thinner than 28 gauge. Residential duct is a code minimum thickness problem, not a reinforcement class problem, and pricing a house off commercial gauge tables overstates the metal significantly.

Pounds or Pieces

The gauge ambiguity is also why the industry has two competing estimating methods rather than one. Joseph D'Amelio of Wendes describes them cleanly. The per pound method applies a blended labor and material cost per pound, built from the typical mixture of gauges, straight duct and fitting types that your company sees on a given system type. It is fast, and it is accurate exactly as long as the job in front of you resembles the jobs the rate came from. When the mixture shifts, the per pound cost drifts with it in a way that is hard to see.

The per piece method prices each duct piece and fitting by its actual type and size, from time studies broken into component fabrication and installation operations. It compensates automatically for an unusual mixture of sizes, gauges and fitting types, which is precisely the case where a per pound rate quietly fails. It takes longer and it is more accurate.

A reasonable working rule: per pound for conceptual and budget numbers on work that looks like your normal work, per piece for hard money bids and for anything with an unusual fitting density, an unusual size range or a material you do not normally run.

The counted families are where the dollars concentrate, and reading the schedules properly is most of the work.

The Mechanical Equipment Schedule

This is the single most important sheet in the set for your bid. It lists every piece of equipment by tag with its capacity, airflow, electrical characteristics, physical data and usually a basis of design manufacturer and model.

Take it off tag by tag and capture, for each one:

• -Tag, quantity, and the type of unit
• -Nominal capacity in tons or MBH, and design airflow in CFM
• -Electrical: voltage, phase, MCA and MOCP, because these determine whether the electrical scope you are assuming is adequate
• -Weight, which drives rigging and structural questions
• -The listed model and whether substitutions are permitted, which is in the specification rather than on the schedule

Then read the notes. Schedule notes are where the expensive scope hides: factory options, controls packages, economizers, smoke detectors, filter types, warranties, seismic requirements, startup and commissioning obligations.

Equipment Sizing Is Not Your Takeoff, But Read It Anyway

On design build and residential replacement work you may be the one sizing the equipment, and this is where rules of thumb cost real money. The numbers here are genuinely worth knowing.

On the sizing side, ACCA's HVAC Blog published load calculation data from Energy Vanguard covering 40 Manual J calculations, mostly in the Southeast and Texas plus some California and Midwest projects. The average result was 1,431 square feet per ton, with a range from a low of 624 to a high of 3,325. The rules of thumb contractors commonly reach for are 400 to 600 square feet per ton. Not one of the 40 calculations came in as low as the high end of the rule of thumb range. Their conclusion was blunt: if you get a number under 1,000 square feet per ton, there is a good chance the number is wrong.

On the airflow side, the familiar 400 CFM per ton has a traceable origin worth understanding. Trane's engineering documentation tracks it back to the 1971 ASHRAE Handbook of Fundamentals, which stated that total residential cooling load is usually calculated as 1.3 times sensible load, implying a sensible heat ratio of about 0.77. The 1989 Handbook states that equipment is usually designed for a standard operating condition of 80 degrees dry bulb and 67 degrees wet bulb entering the coil, 400 CFM per ton, and a sensible heat factor of 0.77. Equipment has for decades assumed roughly a 400 CFM per ton plus or minus 20 percent operating range. Two things follow. First, every one of those references is residential, not commercial. Second, it is a coil design assumption, not a law, and it breaks down when the actual sensible heat ratio of the space differs from 0.77.

For a takeoff, the practical use is as a sanity check. If the schedule shows 3,000 CFM against 5 tons, that is 600 CFM per ton and something unusual is going on with the latent load or the selection. Ask the question before you price it.

The Air Device Schedule

Diffusers, registers and grilles are counted, and the count is drawn from two places that have to agree. The air device schedule gives you type, neck size, face size, material, finish, mounting and design CFM for each tag. The reflected ceiling plan gives you how many of each tag exist and where.

Count from the ceiling plan, verify against the schedule, and reconcile any difference with an RFI rather than a guess. Watch for:

• -Neck size versus face size. A 24 by 24 lay-in diffuser with an 8 inch neck is a 24 by 24 device and an 8 inch runout. Both numbers matter and they belong on different lines.
• -Finish and border type. Lay-in, surface mount and plaster frame versions of the same device are different prices and different part numbers.
• -Devices on non-ceiling surfaces. Sidewall registers, floor registers, door louvers and transfer grilles are easy to miss because they are not on the ceiling plan.
• -Devices in the drawing that are not in the schedule. It happens on nearly every tenant improvement set.

Derived Accessories

Once you have duct lengths and device counts, most of the remaining material falls out of them mechanically:

• -Volume dampers, typically one per branch runout, so the count follows your runout count
• -Spin-in takeoffs or collars, one per round branch off a trunk or plenum
• -Flex connections, at each equipment inlet and outlet
• -Turning vanes, at square throat elbows
• -Access doors, at every damper, coil, smoke detector and anything else requiring service access
• -Hangers, a function of duct length and spacing, covered in the reference tables below
• -Sealant, a function of joint and seam length, which is itself a function of duct length and section length

The ones that do not fall out mechanically are fire dampers, smoke dampers and duct penetration firestopping, because those are determined by the rated assemblies the duct crosses. They come from the life safety plan and the wall schedule. There is no way to derive them from a duct quantity, which is exactly why they get missed.

A 9,000 square foot single story office tenant improvement. Two rooftop units, ductwork above a lay-in ceiling, supply and return at 1 inch water gauge. All arithmetic shown so you can check it.

Equipment, Counted

Attached to those four units: 2 roof curbs, 2 sets of curb flashing, 4 flex duct connections at the rooftop supply and return, 2 condensate traps and piping runs, 2 roof penetration assemblies for the exhaust fans. Ten additional material lines generated by four pieces of equipment.

Rectangular Duct, Measured and Converted

Check one line by hand. The 12 by 10: (12 + 10) / 6 = 3.667 square feet per foot. Times 80 feet is 293.3 square feet. Times 1.156 pounds per square foot is 339.1 pounds. Every row works the same way.

Round Branch Runouts

120 linear feet of 8 inch round in 24 gauge, feeding the diffusers.

Geometric: pi x 8 / 12 = 2.09 square feet per foot, times 120 = 251.3 square feet, times 1.156 = 290.5 pounds.

From SMACNA Appendix A-10: 8 inch round in 24 gauge is about 2.57 pounds per foot, times 120 = 308.4 pounds.

Use 308 pounds. The 18 pound difference is the seam laps, and this is the honest version. On a job with a lot of small round it is worth using the published table rather than the bare circumference.

Totals

• -Surface area: 1,548.3 + 251.3 = 1,800 square feet of sheet metal
• -Installed weight: 2,041.1 + 308.4 = 2,350 pounds
• -With 12 percent scrap and drop: 2,350 x 1.12 = 2,632 pounds purchased

The 1,800 square foot figure is not a byproduct. It is the number that prices insulation, liner and sealant, so keep it. The 2,350 pound figure prices metal and drives the labor tables. The 2,632 pound figure is what you buy.

Fittings, Counted by Piece

Fittings do not get measured into the linear footage. They get counted, and their weight and labor come off a fitting table or a per piece rate. A shop that lumps fittings into straight footage at the same rate per pound is underpricing the fitting-dense areas and overpricing the long straight runs.

Air Devices, Counted

Twenty-four supply diffusers means 24 runouts, 24 spin-in takeoffs and 24 volume dampers. That is the chain reaction the device count sets off, and it is why the device count gets done before the accessory takeoff rather than after.

Hangers

Rectangular duct at 8 foot maximum spacing: 275 / 8 = 34.4, round up to 35 pairs. Round runouts at 10 feet: 120 / 10 = 12. Total 47 pairs, call it 50 with extras at fittings, direction changes and the drops through the roof curbs.

Size them off perimeter, not off weight. SMACNA Table 4-1 keys rectangular duct hangers to the maximum half of duct perimeter. For the 30 by 12 trunk, half the perimeter is 42 inches, which at 10 foot spacing falls in the range served by a 1 inch by 18 gauge strap or a 3 eighths inch rod. Note that half the perimeter is (W + H), which is six times your square feet per linear foot figure. One measurement, three uses.

Insulation

Not all 1,800 square feet gets wrapped. Only the duct the code and the spec say to wrap. Assume the drawings show R-6 external wrap on the 1,200 square feet running above the ceiling in the unconditioned plenum and on the short vertical legs at the curbs, and nothing on the rest.

1,200 x 1.10 for overlap and stapling flange = 1,320 square feet of duct wrap.

What the Bid Sheet Now Holds

Four pieces of equipment, ten equipment-attached items, 2,632 pounds of galvanized purchased, 51 fittings, 36 air devices, 24 volume dampers, 50 hanger pairs, 1,320 square feet of wrap, plus sealant, fasteners and the accessories from the next section. Every one of those numbers traces back to either a schedule tag or a measured length times a published constant. Nothing was guessed.

Everything you need to do the conversion without software. Print it.

Rectangular Duct: Square Feet per Linear Foot

SF per LF = (W + H) / 6, inches. Verified against SMACNA Appendix A-7.

Round Duct: Square Feet per Linear Foot

SF per LF = pi x D / 12.

Galvanized Sheet Weight, Pounds per Square Foot

SMACNA Appendix A-2 nominal values.

Rectangular Duct: Pounds per Linear Foot

The two tables above, multiplied. Multiplying SMACNA's own surface area values by its own sheet weights reproduces its Appendix A-8 weight table digit for digit, so this arithmetic is the standard's arithmetic.

Hanger Spacing and Sizing

Per SMACNA Chapter 4. Section 4.2.8 explains the logic: a straight duct section is effectively a box beam, the joint is the weakest point, so that is where the support goes, and joints are normally strong enough for maximum hanger spacing at 8 or 10 foot intervals. Very wide ducts need closer spacing to keep individual hanger loads safe.

Table 4-1 sizes hangers off maximum half of duct perimeter, P/2:

Single hanger maximum allowable loads, same table: 1 inch by 22 gauge strap 260 pounds, 1 inch by 18 gauge 420 pounds, 1 inch by 16 gauge 700 pounds, 1.5 inch by 16 gauge 1,100 pounds. Rods: 1 quarter inch 270 pounds, 3 eighths inch 680 pounds, 1 half inch 1,250 pounds, 5 eighths inch 2,000 pounds.

Vertical risers are a separate rule. SMACNA section 4.2.10 puts riser support intervals at one or two story intervals, 12 to 24 feet, as suits the loading. It also warns that for ducts over 30 inches wide, sheet expansion under internal pressure tends to tear support fasteners out, so the attachment method matters.

Flex Duct: What the Code Actually Limits

This is the most commonly misquoted rule in the trade. Per IMC 2024 section 603:

Flexible air ducts and flexible air connectors are two different listed products, and the 14 foot limit belongs to the connector. That said, energy codes, ACCA duct design and many project specifications impose their own flex length limits, and a long lazy flex run is a pressure drop problem whether or not the mechanical code caps it. Read the spec.

Duct Insulation

The IECC commercial provision for duct and plenum insulation, section C403.11.1, sets the baseline:

Exceptions are duct located within equipment, and duct where the design temperature difference between inside and outside the duct is not greater than 15 degrees F. Verify against your adopted code, because state amendments and California Title 24 differ.

Measure wrap and liner in square feet off your duct surface area figure, and add for overlap and the stapling flange on external wrap. Liner does not get the same allowance and it reduces the free area of the duct, which is a design issue rather than an estimating one.

Labor Units, For Context

You will see SMACNA labor units referenced constantly. Their Reference Manual for Labor Units carries 138 tables covering fabrication and installation of duct, fittings, hangers, equipment and accessories, in pounds per hour and hours per piece, assembled originally from a survey of over 300 member firms. Three points matter for how you use them:

• -They are a benchmark at 1.0, meant to be factored against your own historical field feedback
• -SMACNA rates project difficulty as normal, difficult or very difficult, and treats all remodel work as difficult or very difficult. Running a retrofit at 1.0 understates it by definition
• -The units exclude engineering, supervision, field layout and detailing, and non-standard construction. Those are separate lines, not absorbed

The quantities that sink HVAC bids are rarely the ones on the mechanical sheets. They are the ones that live somewhere else, or nowhere.

Vertical Feet

Same structural problem every trade has. A floor plan is a horizontal projection, so the drop from a trunk to a ceiling diffuser, the riser up a shaft, the leg down through a roof curb into the building and every offset around a beam or a light fixture read as a dot rather than as footage. Get those feet from the sections and the mechanical riser diagram. A quick self-check on a small job: divide total duct footage by air device count and compare it against your own history. Low ratio means you missed drops.

Fire and Smoke Dampers

There is no way to derive these from a duct quantity. They exist where duct crosses a rated assembly, which means the quantity comes off the life safety plan and the wall types. Trace every penetration. Then add the access door that each one requires, the firestopping at the penetration, and the sleeve or retaining angle. One damper is four material lines.

Coordination Scope on Other Trades' Drawings

Take one deliberate pass through the architectural, structural, electrical, plumbing and kitchen sheets looking only for things that connect to your work:

• -Kitchen equipment with hood and makeup air requirements, on the kitchen equipment schedule
• -Equipment condensate, which may be your pipe or the plumber's depending on the spec
• -Electrical disconnects, starters and line voltage to your units, which are often on the electrical drawings but sometimes written into your specification section
• -Louvers and wall openings, which may be architectural scope, yours, or split
• -Roof curbs and structural framing for rooftop equipment, which is a classic split scope fight
• -Ceiling access panels required to service your dampers and coils

The Rest of the Checklist

• -Roof curbs, curb adapters and rails. On a changeout the existing curb rarely matches the new unit footprint.
• -Crane and rigging. A rooftop pick is a real cost with a real schedule constraint and it is nowhere on the mechanical plan.
• -Sealant and gasket. A function of joint and seam length. Cheap per unit, large in aggregate on a job with thousands of feet of duct.
• -Test and balance. Specified work, usually a separate subcontract, frequently left out of the base number.
• -Duct leakage testing. Where the spec or the energy code requires it, it is enumerated scope with real cost.
• -Startup, commissioning and owner training. Read the specification section, not the drawings.
• -Controls. The line between your scope and the controls contractor's is the single most common scope gap in mechanical bidding. Thermostats, sensors, control wiring, actuators and the front end all need an owner named in writing.
• -Temporary heat, temporary filtration and protection of installed duct. Often in the general conditions, sometimes pushed down to you.
• -Demolition of existing equipment and duct, including disposal and refrigerant recovery.
• -Access for the work itself. Attic, crawlspace, occupied building, night work, elevator versus stairs. This does not change your material quantities at all and changes your cost substantially.

(A tool that reads quantities off a PDF will find the duct that is drawn, and that is genuinely most of the tedium gone. It will not find the fire damper that exists only as a note on the life safety plan, or the controls sentence buried in Division 23 that just made the thermostats yours. The checklist above stays a human pass no matter what you take off with.)

Two Habits Worth Building

First, keep your own conversion factors. The published numbers in this guide are exact where they are geometry and conventional where they are shop practice. Square feet per linear foot is arithmetic and will never change. Pounds per square foot by gauge is a published material property. Scrap percentage, fitting allowances, gauge selection and labor factors are properties of your company, and the only way to get them right is to compare what you bought against what you installed, job after job, and write the ratio down.

Second, hand check the two or three quantities that carry the most dollars, every single time, regardless of where the numbers came from. On an HVAC job that is almost always the equipment count, the main trunk footage and the air device count. Equipment because it is the largest dollars per line. Trunk footage because it is the largest weight. Device count because it silently multiplies into runouts, takeoffs and dampers. If those three are right and everything else is close, the bid holds. If the trunk footage is wrong, nothing downstream saves you.