Heat can be lost as follows

• by conduction through the building fabric
• by convection through ventilation losses associated with poorly fitting windows and external doors

The role of insulation is to reduce the rate of at which heat flows by conduction. The opening and closing of windows will alter the ventilation. If there is no ventilation vent the window will need to be open sufficiently to give good air quality but not too far to prevent unnecessary heat loss.

Convection losses can be reduced by adding a sealant strip between the window frame and the wall and between the window and the frame.

Radiation losses can be reduced only by reducing the rate of heat flow through the building fabric.

criteria	economics
installation	advice