Heat Loss Calculation
/ heet loss kal-kyoo-LAY-shun /
Also known as: heat loss survey, room-by-room heat loss
Definition
A heat loss calculation works out how much heat each room and the whole building loses through walls, roof, floor, windows and ventilation at a design outdoor temperature. The result gives the heat output needed to keep the building comfortable and is used to size the heat pump or boiler and the radiators or underfloor heating.
In practice
The calculation uses the dimensions, construction and U-values of each element, the air tightness and ventilation, and the design temperatures. Done properly it is room by room, not a rule of thumb based on floor area. Installers certified under MCS are expected to carry one out for a heat pump installation.
An oversized heat pump cycles on and off and wastes money, while an undersized one cannot meet demand on the coldest days. Improving insulation reduces the heat loss and so the size and cost of the system, which is why the calculation is often best done before upgrade work is finalised.
Building Regulations
Methods and standards are updated from time to time. Ask your installer to share the calculation and the assumptions used.
Full guide: Heat pumps for UK homes