Size any furnace, heat pump, or mini-split correctly in seconds — room by room, right in your browser.
Get Instant Access — $19✓ Works instantly in your browser — no account needed
Most contractors still size systems with a "rule of thumb" that leads to short-cycling, humidity problems, and blown budgets. This calculator gives you a real load estimate based on square footage, insulation, windows, and your climate zone — no spreadsheets, no expensive software.
Get a defensible BTU load and equipment tonnage so you never over- or under-size a system again.
Hand clients a room-by-room breakdown that justifies your recommendation and beats guesswork quotes.
Skip the $500 Manual J software and hours of setup. Enter your details and get results instantly.
Add each room's square footage, insulation level, window count, and your climate zone.
The tool runs a Manual J Lite load estimate for heating and cooling instantly.
See the recommended BTU load and equipment tonnage for a furnace, heat pump, or mini-split.
One-time purchase. Unlimited calculations. Works instantly in your browser — no account needed.
Get Instant Access — $19This is a "Manual J Lite" estimator built for fast, practical sizing of residential systems. It uses the same core inputs — area, insulation, windows, and climate zone — to give a reliable BTU load and tonnage. For permit submissions requiring a certified full Manual J, use it as a fast pre-check.
No. It works instantly in your browser — no account, no downloads, no setup. Just open it and start calculating.
Yes. The output gives you the heating and cooling BTU load plus equipment tonnage, so you can size a furnace, central heat pump, or ductless mini-split from the same result.