Cavity Wall Insulation
Roughly a third of all the heat lost in an un-insulated home is through the walls. Insulating cavity walls reduces heat loss and the cot of installation can be recouped very quickly through savings on your fuel bills.
If your home was built from 1920 onwards, there is a good chance that its external walls are made of two layers with a small gap or `cavity' between them. Insulating your cavity walls means filling that gap with a material that traps heat within the house.