Glossary · Heating, cooling & ventilation
Heat-loss calculation
Also called: heat-loss calc · heat loss and heat gain calculation · room-by-room heat loss
A calculation of how fast a home loses heat on the coldest days it's designed for, used to size heating equipment correctly.
What it means
It adds up heat flow through walls, roof, floors, windows and doors plus air leakage and ventilation at the local design temperature, giving the heating capacity the house needs in BTU/h. In the US the usual method is ACCA Manual J, which also works out the cooling load.
Why it matters in an audit
Sizing a heat pump or furnace from a proper heat-loss calculation, rather than matching the old equipment, avoids oversizing and helps rebate-funded upgrades perform as promised.
In the United States
US contractors use ACCA Manual J for the same purpose (see load calculation).