Chimney-Wall Condensation

I changed my standard brick fireplace to a gas one. I installed a liner on the inside of the chimney, but I am finding condensation between the liner and the chimney wall. It does not matter if it rains, or snows, or is dry, there is always condensation. Why has the liner not helped?

Too much cold air at the top of the chimney has created condensation. Older houses typically had the fireplace and the chimney in the middle of the house. This meant that any heat loss through the masonry would remain in the house. Newer houses have the fireplace and chimney on the outside walls, so some heat will exit the masonry and stay in the house, but some will leave the house through the outside wall. The end result is condensation. This happens with all new houses, but there must be something else happening that is leading to the amount of condensation you describe. My guess is that the liner is not properly sealed at the top and bottom of the chimney. If that is the case, cold air is entering the space between the liner and the chimney wall from above, and moist household air is entering from the bottom. If you seal the area where the liner and chimney meet, you should stop the condensation.

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