Manual J calculator

Room-by-room residential load calculation per ACCA Manual J, eighth edition — with the outdoor design temperatures for your county, not a national average.

The calculator is in final testing.

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Load calculation basics

What does a Manual J calculator do?: It computes how much heating and cooling a specific house needs — the load — from square footage, insulation levels, window area and orientation, air infiltration, and local outdoor design temperatures. The result, in BTU/hr, is what correctly sizes the equipment.
Is a rule of thumb like '500 square feet per ton' good enough?: Not for a permit, and usually not for the house. Rules of thumb routinely oversize by 30-50%, which means higher bills, worse humidity control, and short-cycling equipment. Building code (IRC M1401.3) requires sizing per ACCA Manual J and S.
Will the output be accepted for my permit?: Plan reviewers want a room-by-room Manual J eighth-edition report with the design conditions shown. That is the format we produce. Requirements vary by jurisdiction — some also ask for Manual S equipment selection, which is on our roadmap.
What do Manual J services normally cost?: Typical services charge $79 to $300 per report and quote turnarounds from 48 hours to two weeks. Software licenses for doing it yourself run hundreds per year and take real training.