The modern Manual J. Engineer-grade math, contractor-grade UX.
Built for residential HVAC contractors who want a load calc they can trust — and explain. Transparent physics, not a black box.
Transparent math
Every BTU traces to physics — Q = U·A·ΔT, infiltration, ventilation, solar. No black-box AI. Open the breakdown on any result.
Validated ±5%
Calibrated against the NREL/DOE federal MJ8 reference house. 98 automated tests on the load engine.
Fast & mobile-first
Five steps to a sized load on any device. Printable permit-style report. No desktop install, no training.
FAQ
Is this ACCA-approved for permits?
Not yet — ACCA software approval is a separate certification we're pursuing, and Kappa's output is not a stamped engineering document. Important: some jurisdictions require ACCA-approved software output and/or a sizing calculation signed by a licensed contractor or professional engineer (Florida, for example). Always confirm your local building department's requirements. Today Kappa is a fast, transparent estimating and design tool — use it to size confidently and pair it with your approved workflow.
What method does it use?
The ACCA Manual J 8 residential method, built from public engineering sources (ASHRAE Fundamentals, NREL/DOE, IECC). Heating and cooling, sensible and latent, equipment sizing with Manual S.
How is it different from Wrightsoft / CoolCalc?
Web-native, mobile, and transparent. No desktop license, no per-project math that punishes volume, and a results page that shows the work instead of hiding it.
Do I need an account?
No. The calculator is free to run right now. Accounts and paid plans (saved projects, branded reports) are rolling out next.
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