HVAC Cost

What Drives Cost Per Foot of Fabricated Duct and Air Handling Assemblies

A money-focused breakdown of what fabricated duct and air-handling assemblies actually cost to build, and how to quote them without leaving margin on the floor.

Fabricated duct cost splits into four buckets that a defensible quote must show separately: material, direct labor, machine and shop time, and loaded overhead. On a typical low-pressure commercial job, galvanized steel runs 35 to 45 percent of cost, fabrication labor 25 to 35 percent, insulation and sealant 8 to 15 percent, and overhead plus margin the rest. When coil stock jumps from 1.15 to 1.55 dollars per lb, a job that was 40 percent material can swing 12 to 14 percent on total price overnight, so lock material pricing to the quote date and note the expiry.

Material cost is yield times price, and the yield is where money leaks. Buy steel by the pound, not the finished foot. At 4.3 lb of 24 gauge per finished square foot and 1.25 dollars per lb, raw material is 5.38 dollars per square foot before scrap. If nesting yield is 85 percent rather than the 92 percent you assumed, real material cost climbs to 5.83 dollars, a 45 cent per square foot miss that on a 640 square foot job is 288 dollars of unrecovered steel. Run the Duct Sheet Yield calculator on the actual sheet sizes you stock so scrap is priced in, not hoped away.

Labor is billed in shop hours, so convert every fitting to a time standard. A straight rectangular section might take 0.15 hour to fabricate, a square-to-round transition 0.8 to 1.2 hours, a radius elbow with turning vanes 1.0 to 1.5 hours. At a fully burdened shop rate of 55 to 75 dollars per hour, a job with 40 straights and 12 transitions is roughly (40 times 0.15) plus (12 times 1.0) equals 18 hours, or 990 to 1,350 dollars of labor. The Assembly Labor calculator lets you attach standards per fitting type so the quote reflects the actual mix, not a flat per-foot guess.

Machine and shop time is the constraint you pay for whether or not you sell it. A coil line running at 40 to 60 feet per minute and a plasma table cutting blanks both meter your capacity in dollars per hour of occupancy. If the shop carries 180,000 dollars of monthly fixed cost across 3,000 productive machine hours, that is 60 dollars per hour of burden that every job must absorb. The Shop Throughput calculator ties feet per shift to that burden so you can see when a rush job that ties up the line for 6 hours quietly costs more than the overtime it saves.

Scrap and rework are real dollars, not a rounding error. Budget 8 to 12 percent scrap on rectangular duct and 12 to 18 percent on spiral and fittings where offcuts are harder to nest. A failed leakage test is the expensive kind of rework: pulling a section, re-sealing seams, and re-testing can burn 1.5 to 3 labor hours plus sealant, so a 3 percent field failure rate on a 200 section job is 6 rebuilds and up to 18 lost hours. Price a first-pass quality assumption explicitly rather than absorbing failures into margin.

Sealant and insulation are small line items that get skipped and then eat the margin. At roughly 300 feet of joint per gallon and 45 to 60 dollars per gallon, sealant is often only 0.20 to 0.35 dollar per finished square foot, but a job with dense fittings can double that joint length. Insulation swings wider: 1.5 inch wrap at R-6 runs 0.55 to 0.90 dollar per square foot installed, and a spec jump to R-8 or a rigid board liner can add 40 percent. Quote both from the Sealant Usage and Insulation Cost calculators rather than a flat percentage add-on.

Build the quote bottom-up and let it roll into a per-unit number you can defend. Sum material, labor, machine burden, scrap, and consumables to get true cost, then apply target margin. The Cost Per Unit calculator divides fully loaded cost by finished square feet or by each, so you quote 14.50 dollars per square foot knowing 8.20 is material and labor and 3.10 is burden. When a customer pushes on price, you can point to the line that moves, usually gauge or insulation spec, instead of shaving margin blindly.

The three estimates that go wrong most: assuming yield instead of measuring it, quoting labor by the foot when the fitting mix is transition-heavy, and forgetting that fan static drives motor and energy cost the owner will scrutinize. A quote that under-costs transitions by 0.5 hour each on a 20 transition job loses 550 to 750 dollars before you notice. Re-price any bid where material plus labor lands under 60 percent of the sell price, because that usually means overhead and scrap were buried, not covered, and the job will finish at breakeven or worse.

Published 2026-07-01.