How Does Heat Loss Occur?

As Autumn continues to creep across Europe, we are exploring how heat loss occurs from building. In part one we discussed how to reduce heat loss. In part two we learned about thermal bridging and condensation in more detail. Today we talk about the two methods which causes heat loss. 

Heat Loss in buildings

Heat Loss = Conduction + infiltration

There are two methods of heat loss through the building envelope. These are heat loss through conduction and heat loss through infiltration.

Heat Loss through conduction

This is heat loss occurring through the building fabric via conduction usually occurring on the exterior surface of floor, walls, roof, and windows.

Heat Loss Q_F=U×Area×∆T (W)


              U = Thermal transmittance of building element (W/m2K)

              A = Surface area of building element (m2)

             ΔT = Temperature difference inside to outside (K)

              W = Watts


This is warm air escaping the building through uncontrolled gaps and being replaced by colder  outside air.

This can be calculated using the formula:

Infiltration Heat Loss  Q1=(N×V×∆T)/3 (W)

N = Number of fresh air changes per hour

V = Volume of the inside space (m3)

K = Degrees Kelvin

W = Watts

Luckily, here at GES Energy we are here to do the calculations for you! To learn more about how you can reduce your buildings heat loss please contact GES Energy today on

Air infiltration at base of an entrance door.

Air infiltration at base of an entrance door.