Draught stripping  
 

According to the Energy Saving Trust, in a typical home 20 per cent of all heat loss is through ventilation and draughts. Draught proofing is one of the most effective of energy saving measures, not least because it directly affects comfort. Sitting in a draughty room is unpleasant and expensive.

Draught stripping is most commonly used the fill gaps around windows and doors. For more information click here.
Gaps between floorboards and skirtings are often a source of draughts. These can be filled with a silicon sealant.

Watchpoint: draught seals should not be painted over. Compression seals should deform to fill a gap when a door or window is closed. Paint will make them stiff and they just will not work-time to replace! For more information click here.

Watchpoint:
Leave sufficient ventilation in place. See ventilation.

The Draught Proofing Advisory Association is also a good source of information