Draught Heat Loss Calculator

• February 14, 2022 - Leo Rampen

Heat loss through “air changes” - air flowing out of a house through draughts, vents and holes - is huge. An old and unimproved house might have 4 air changes every hour. For a typical 3 bed house on a cold 0 degree C day, that means 6 - 8kW being lost through leakage alone.

Use this interactive calculator to estimate how much heat is being lost in your house.

Air Changes per Hour

This is the number of times (on average) all the air in the house is replaced by outside air. A higher number means more heat lost. This is tested at a slight pressure - 50 Pa - which is enough to give very strong draughts. The air changes at 50 Pa is approximately 20x the actual air change figure. However, the air leakage test normally requires all “intentional” ventilation (eg trickle vents, extractor fans) is blocked up - this will add significantly to the actual air change in the house.