Calculators only earn trust once
A wrong tonnage reading means someone orders the wrong part. A wrong superheat number means someone chases a fault that isn’t there. So no tool goes live on DuctMath until its math engine passes a written test suite — and the suite itself is published on this page, so you can check our work instead of taking our word for it.
The method
Every calculator’s logic is tested three ways before launch:
- Known-answer cases. Real inputs with verified answers — actual model numbers from the six major North American brands, published pressure–temperature points — must decode to the correct result.
- Trap cases. Inputs specifically designed to fool lazy logic: SEER digits that masquerade as size codes, brand series numbers that collide with capacity codes, readings that produce negative results.
- Boundary cases. Empty inputs, out-of-range pressures, and nonsense strings must fail safely with a useful message — never a wrong number presented confidently.
Published results
AC Tonnage Calculator by Model Number — v1.0: 13/13 passed
Sample cases from the suite (expected → result):
- Trane 4TTR4036L1000AA → 3.0 tons ✓ (capacity code embedded in a longer digit run)
- Goodman GSXC180601 → 5.0 tons ✓ (the “18” is SEER, not size — the classic trap)
- Carrier 24ACC636A003 → 3.0 tons ✓ (leading “24” is a series number, not 2 tons)
- Rheem RA1418AJ1NA → 1.5 tons ✓ · Lennox XC16-036-230 → 3.0 tons ✓ · York YCG36B21S → 3.0 tons ✓
- Empty input and no-digit strings → safe “no match” message, never a guess ✓
Superheat & Subcooling Calculator — v1.0: 10/10 passed
- R-410A 118.3 psig → 40.0 °F saturation ✓ · R-22 68.5 psig → 40.0 °F ✓ (chart anchor points)
- Interpolation between chart rows (125 psig → 42.8 °F) ✓
- Worked example round-trip: 50 °F line at 118.3 psig → exactly 10.0 °F superheat ✓
- Negative superheat correctly detected and flagged as a floodback alert, not displayed as a normal reading ✓
- Out-of-range pressures rejected with a pointer to the PT chart, both refrigerants ✓
- Both PT tables verified strictly monotonic (no data-entry errors) ✓
Stated limits
Honest tools declare their edges. Current known limits, stated on the tool pages themselves: PT values are sea-level and shift slightly at altitude; the superheat tool covers verified R-410A and R-22 tables only — R-32 and R-454B will be added with properly verified data rather than approximations; model-number decoding covers standard residential conventions, and unusual light-commercial formats may require the AHRI Directory. When a rule of thumb appears (like BTUs per square foot), it is labeled a rule of thumb.
Corrections and changelogs
Every error report sent through the contact page is run against the tool’s test suite. Confirmed errors become new test cases — so a mistake, once fixed, can never silently return — and the fix ships with a note in that tool’s changelog. Updates always carry fresh examples, never just a new date.
Independent review
Test suites catch math errors; field experience catches the rest. DuctMath tool pages are open for technical review by licensed HVAC contractors and technicians — reviewers check the assumptions, targets, and terminology against how the work is actually done, and receive a named credit on the pages they review. Working in the trade and want to review a tool? Get in touch.