HVAC Heat Loss & Heat Gain Calculator (Manual J)
Calculate whole-house heating BTUh heat loss and cooling heat gain tonnage under ACCA Manual J standards, climate design temperatures, and insulation ratings.
Calculated Results
Frequently Asked Questions
What is an ACCA Manual J residential load calculation?
ACCA Manual J is the official industry and building code standard for sizing residential heating and air conditioning systems. It calculates peak heat loss in winter and peak sensible/latent heat gain in summer based on the building envelope.
Why is an oversized HVAC system bad for a home?
An oversized air conditioner short-cycles (turns on and off rapidly), failing to run long enough to dehumidify the air. This leads to cold, clammy rooms, high indoor humidity, mold growth, premature compressor failure, and high electricity bills.
How many BTUs of heating and cooling are needed per square foot?
Depending on climate and insulation, heating loads range from 20 to 45 BTU/sq ft, while cooling loads range from 15 to 25 BTU/sq ft (or roughly 500 to 700 square feet per 1 ton of AC cooling).
How do windows impact summer heat gain?
Solar radiation entering through standard non-Low-E windows can account for up to 40% to 50% of a home's entire summer cooling load. Upgrading to Low-E windows with a low Solar Heat Gain Coefficient (SHGC < 0.25) significantly reduces AC equipment sizing.