"Christian McArdle" wrote:
In fact, our back room has such a vent for its old fireplace and it is
much
superior to the front room wall vent. The front room vent is capable of
producing hurricane force cold winds in winter.

Christian.

Yes, my experience exactly.
Dining room has floor ventilation and is hardly noticeable in winter.
Lounge has 4 inch diameter wall hole ventilation and it would be like
sitting in a cold store during winter but for the fact that I block it off.