AI for sheet metal contractors, tested on duct takeoffs you already bid.

Your closed work is the answer key. Each bid your estimators finished left a takeoff carrying the calls they made, and each tested system left a report someone built from field sheets. A reviewer can hold every draft against work that already went out the door.

The trade's own books are only the start. SMACNA's technical resources page keeps separate shelves for architectural sheet metal, HVAC duct construction and industrial duct construction, and a commercial shop can need all three on one project. Those books move as well. The fourth edition of HVAC Duct Construction Standards, Metal and Flexible, reported by ACHR News in October 2021, runs 416 pages and added spray and aerosolized sealants, tables for spiral flat oval duct and liner rules for non-fiberglass types.

Then each owner writes over them. The University of Arizona's design manual still files ductwork under Division 15, as Section 15840, in a revision dated April 2026, so anyone hunting for 23 31 13 can walk past it. Washington University School of Medicine's design standards allow no duct liner at all, exterior insulation only, and want static pressure classifications noted on the drawings. A takeoff has to follow that owner's words, system by system, and not the shop's habits from the last job.

Hospitals and labs bring their own exhaust rules. An addendum to the 2008 edition of ASHRAE Standard 170 lists exhaust from airborne infection isolation rooms, bronchoscopy rooms and laboratory fume hoods among the discharges whose duct must stay under negative pressure in occupied space, with any positive-pressure stretch in a mechanical room sealed to SMACNA Seal Class A. A 2010 bulletin on the National Institutes of Health's design requirements rules out irregular or makeshift fittings and expects a documented pressure loss coefficient for each one.

The testing lands on your crew. That same NIH bulletin has the sheet metal contractor pressure test installed duct and quantify the leak rate, and the University of Michigan's duct design guideline requires leakage testing on all but very small projects. Each test leaves a sheet, and somebody in your office turns the stack into the report an engineer can accept. Damper paperwork follows close behind: the medium-pressure duct section for Massillon West Elementary in Ohio has the sheet metal contractor set the automatic dampers the controls contractor furnishes, then certify by letter that every fire damper is installed and working.

One limit covers both jobs. The proof of concept works on copies. It never touches your estimating, detailing or job cost system, a live bid or a live report, and it never decides that a duct system passed a test or meets a code. An estimator checks every takeoff and a qualified tester signs every report. Rules named on this page are examples from published documents, not legal or engineering advice.