What DuctMath is
DuctMath is a free toolbox of HVAC calculators and decoders — the everyday math of sizing, airflow, and refrigerant, rebuilt as fast single-purpose tools that work on a phone in the field. No accounts, no downloads, no paywalls.
Why it exists
The site comes out of years of working with heating and air conditioning contractors across the United States on their marketing and lead tracking. The same pattern kept showing up: the technical answers techs and homeowners need — what tonnage a model number encodes, whether a charge reading is normal, what size duct a room’s CFM calls for — live in scattered PDFs, laminated truck charts, and forum threads. Each answer exists, but finding it takes longer than using it.
DuctMath collects those calculations in one place and holds every tool to the same standard: the answer first, the exact formula written out, a worked example with real numbers, and the reference chart printed on the same page so the result can be verified rather than taken on faith.
How the tools are built and tested
Every calculator is written as lightweight, dependency-free code and has to pass a written test suite before it goes live — real model numbers from the major North American brands, published pressure–temperature points, and deliberate trap cases that fool lazier tools. Where a calculation has limits, the page says so plainly: a square-footage rule of thumb is labeled a rule of thumb, and anything that should be confirmed by a licensed professional or a manufacturer’s data plate is flagged.
Found an error, or a case a tool doesn’t handle? That’s exactly the feedback that improves the site — send it through the contact page and it gets reviewed against the tool’s test suite.
Who runs it
DuctMath is built and maintained by Badar Imran, co-founder of a digital agency that serves home-service contractors — HVAC companies most of all — with advertising and conversion tracking. The tools are developed in consultation with the working contractors we serve, and the roadmap is driven by what field technicians and homeowners actually search for, not by what’s easy to build.
What’s next
The current tools cover model-number decoding and refrigerant charge checks. In the workshop now: duct sizing and CFM charts, an AC age decoder for serial numbers, and a quick residential load estimator. New tools are announced on the homepage as they pass testing.