Manual J
Manual J is the ACCA (Air Conditioning Contractors of America) standard for residential heating and cooling load calculations. It is a room-by-room procedure that accounts for envelope conduction, infiltration, solar gain, internal gains (people, lights, appliances), and duct losses, producing both design heating loss (BTU/hr) and design cooling load split into sensible and latent components. Manual J is required for HVAC permits in most jurisdictions and is the rigorous version of the simplified UA-method heat-loss calculations.