Calculate HVAC Load is a free online toolkit for residential and small commercial HVAC sizing. Every calculator on this site runs ACCA Manual J or Manual N style methodology with climate data sourced from ASHRAE design temperature tables, then surfaces results that match how equipment is actually sold and ducts are actually installed — tonnage rounded to the nearest 0.5 ton, CFM at 400 per ton, and round / rectangular duct dimensions at standard residential friction loss.
What we built
Eight calculators that share the same underlying math, so your results stay consistent across tools:
- HVAC Load Calculator — whole-house cooling and heating load with ZIP-aware climate zone
- Manual J Calculator — room-by-room sensible, latent, and total cooling
- Tonnage, BTU, CFM, and duct size calculators for spot-sizing
- Heating Load and System Size for whole-system specs
- Commercial Load for offices, retail, restaurants, and light industrial spaces with ASHRAE 62.1 ventilation
Who it's for
Homeowners use it to verify contractor quotes and avoid being upsold on oversized equipment. HVAC contractors use it for on-the-spot load calculations during sales calls. Engineers and designers use it as a starting point for full Manual J / Manual N documentation, paired with Manual S equipment selection and Manual D duct design.
What we don't do
We don't store your inputs, sell leads to contractors, or run ads against calculator results. Every calculator runs entirely in your browser — your address, square footage, and energy data never leave the page. We don't require an account, an email, or a phone number to use any tool.
How accurate is it?
Within ~10–15% of a full ACCA Manual J on typical homes when inputs are accurate. For permits, rebates, or unusual buildings, you should run a full Manual J via certified software (Wrightsoft, Cool Calc, HVAC-Calc) or hire a credentialed contractor. Our methodology is documented on the methodology page.
Get in touch
Spotted a bug, have a feature request, or want to suggest a new calculator? Hit the contact page — we read everything.