Free tool · ACCA Manual J 8th-edition methodology
Manual J block-load calculator.
Get a whole-house heating and cooling load in about two minutes, from your envelope assemblies, glazing, infiltration and duct arrangement — plus Manual S sizing guidance for the equipment that would serve it. Free, no sign-up.
Where a block load stops being enough
READ THIS FIRSTOne number for the whole house
Good for sanity-checking equipment that has already been proposed, for early budgeting, and for catching an obviously oversized system before anyone orders it. It tells you roughly how much capacity the building needs.
Required for permits and for ducts
A permit office wants loads calculated room by room, and Manual D duct design is impossible without them — you cannot size a branch without knowing the airflow that room requires. That is the report we prepare.
This tool applies first-principles physics — U·A·ΔT conduction, infiltration, code ventilation and solar gain through SHGC — with defaults aligned to ACCA Manual J 8th-edition methodology. No ACCA tables are reproduced. Every field marked default is an assumption you should verify against the actual home.