A typical door has a perimeter of approx 5.6m (18.4ft ). If the gap around the door is 1mm it is equivalent to the area of *a hole with a diameter of 84mm (3.25in)*.

If there is a gentle breeze of 1 m/s ( mph) blowing outside and this is the speed of the draught and it's a cold winters day, close to freezing (1 deg C) then the heat required to raise the temperature to 18 deg C will be approximately **0.15kW**.

If the fuel costs 3.9p a unit for gas central heating then the heating cost would be nearly **0.59p per hour **or** £10 per heating season**.

For electricity this would be **1.6p per hour** or **£27 per heating season.**

Probably of equal importance is the effect of the draught on **comfort**. If the room was 3m (9ft 9in) x 3m (9ft 9in) x 2.3m (7ft 6in) = 20.7 m3 then the air in the room is changing once every hour. It perhaps doesn't sound much but with the heating off, in theory, the room would be the same as the outside temperature in one hour.