An open fire is not a particularly warm thing to have unless you’re directly in front of it. Most of the heat goes straight up the flue, and it uses an enormous amount of air to keep burning - it will pull huge volumes from rvertwhere it can. This is why these old buildings didn’t suffer from damp issues - the open fires burning were ventilating them.

It's the same problem as those portable AC units: the exhaust (chimney in this case) draws large amounts of air in from outside which is at the wrong temperature (cold in this case).

If it has a flue or chimney, it isnt really an open fire. Look at an ancient long house, or farmer's thatched cottage from say 400 years ago. They had a fire on a stone circle on the floor in the middle of the room, and a high roof sometimes with a hole but often not. It was smoky, but kept everyone warm.