Draughts Come From Places You Cannot Feel

A draughty room is losing heated air and drawing cold air in to replace it. The largest of those paths are usually silent and produce no sensation at all.

Air movement needs an inlet and an outlet

Air cannot leave a room unless it can also enter. Warm air escaping high in a building pulls cold air in low down, and the two effects sustain each other.

This means sealing one end changes the flow through the other, and it explains why blocking a single obvious gap often produces less improvement than expected.

The felt draught is usually at the inlet, low down and cold. The larger loss is frequently at the outlet, where the air is warm and moving slowly.

The unfelt paths are the big ones

Gaps around loft hatches, at the top of walls and around pipes entering from above carry a large volume without producing any noticeable movement.

Floorboards over a ventilated void leak continuously along every joint, and the total area of those joints across a room is considerable.

Unused chimneys are among the largest single openings in an older property, drawing warm air upward whenever the room is heated.

Some ventilation is deliberate

Air bricks, trickle vents and extractor fans exist to remove moisture and, where fuel is burned, to supply combustion air. Blocking them causes different problems.

Sealing a room too thoroughly raises humidity, which produces condensation on cold surfaces and mould in the corners where air does not circulate.

The distinction is between uncontrolled leakage, which should be reduced, and controlled ventilation, which should be preserved and used.

Finding the paths

A lit incense stick or a thin strip of tissue held near a suspected gap shows movement that the hand cannot detect, and it works on both inlets and outlets.

Testing on a windy day exaggerates the effect and makes the paths easier to identify than on a still one.

Closing internal doors while testing isolates each room, since air drawn from another part of the flat can mask where the outside air is actually entering.

Cheap fixes in the right order

Sealing the largest gaps first gives most of the benefit, and in most flats that means the loft hatch, the chimney and the gaps where services pass through walls.

Door and window seals come next and are straightforward, though a door that no longer closes evenly needs adjusting rather than packing with foam.

Heavy curtains and a draught excluder are the last layer and address the sensation rather than the loss, which makes a room feel better without much changing the bill.