If you can feel a draught from an unreasonable gap or hole then it needs to be sealed up.
Become a draught detective and keep the breeze outside. Draughts increase the likelihood of lower temperatures in houses. A draughty home costs more to heat because you’re wasting energy.
It’s a common sense definition. If you can feel external air coming in or a clear draught from a gap or hole, then it’s probably a gap or hole that needs stopping.
If an open fireplace isn’t in use, it can cause draughts - so block it off.
Check out the full details on the draught stopping standard.(external link)
Check if a gap is causing a draught by feeling for cold air along the gap with the back of a wet hand - then you’ll find the major culprits.
You don’t need to block up intentional gaps or holes that are part of the construction.