I have a problem with condensation on the wall between my living room and the chimney and I would be grateful for suggestions as to how to tackle this.
Some background: when I bought my house the fireplaces had been removed and the chimneys capped. The chimneys have a vent on the outside wall, and as far as I can tell the chimneys are dry inside.
This was fine by me, but after a few years in the house I redecorated and removed the several layers of old wallpaper on the living room walls and just painted the walls – no wallpaper. Ever since then, if the weather turns warm and humid, especially after a cold spell (it rarely happens in summer), I get condensation on the wall where the chimney flue runs. This is really quite bad and produces a very noticable damp patch.
I'm pretty certain this is just condensation. I think the inside of the chimney gets cold because it's vented to the outside air, and because the wall between my room and the flue is only one brick thick the inside wall gets cold too. Add damp air and you get condensation on the cold bit of the wall.
I believe it's condensation because it doesn't happen when it rains or at all in the summer, only when the weather turns humid after it has been cold. Living as I do in the North-West of the UK that basically means any time in winter when a warm weather front blows in from the Atlantic! I suspect that it didn't happen before I redecorated because the several layers of old wallpaper were acting as an insulating layer so the inside surface didn't get cold enough for condensation to form.
At the moment I deal with it by just turning up the heating, which dries the wall pretty quickly. However it would be nice to have a proper solution but I have no idea what the solution would be. Maybe I should put some thick wallpaper on the wall to insulate it, as it was before I redecorated? Or maybe block off the outside vents and put vents on the inside wall so the air in the chimney doesn't get cold? I did wonder if the entire chimney could just be filled up with the stuff they use for cavity wall insulation, though I suspect that's a silly idea 🙂
Response to comment:
Here is my attempt to illustrate what is happening:
The damp forms inside the house on the wall between the inside of the house and the inside of the chimney.
Best Answer
...This is one school of thought: seal the chimney to prevent air flow. By preventing air flow, you also prevent the flow of moisture the air carries with it, and the formation of condensation on the colder, interior face of the flue. FYI, the insulation you push up into the flue works simply because it blocks the flow of air; insulation 'warms' nothing. What it does is slow heat transfer from warmer to cooler areas.
The second school of thought is to increase air flow. The theory is that, with constant air flow, moisture that settles on the inner surfaces of the flue will be evaporated.
For this system to work, the flue has to pull in dryer, ambient air from a lower floor; this requires creating an opening below the damp area. This is the preferred method in Britain, for example.
Incidently, houses built in the US Northeast throughout the 1800s had just such an air circulation system built into their exterior walls. In old houses, you have a cavity between the brick and the plaster walls and that cavity extends from the basement to the attic. Air in the attic is heated and exits, creating a partial vacuum which draws air in the cavity upwards. As the air is drawn upwards through the wall, it is heated, which increases its capacity to absorb moisture. This wicking system removes moisture from the inside surface of the brickwork and prevents moisture setting into the lathe.