Question: We recently remodeled our home. Had fireplace (on exterior wall) flue capped at top. Installing vent free gas logs this Fall. However- while running home air conditioner have experienced condensation problems - so bad that the adhesive holding the top piece of marble around the top of the FP opening failed- causing the marble to slip. Question: Should I unseal the flue? Hate to do this due to heat loss. However- I'm afraid that the opposite will occur during cold weather (fireplace cold - home interior warm. Have not reinstalled glass doors yet. Could they be the fix we need. Also getting odor from FP. Your response would be appreciated. I'm so frustrated I am inclined to tear the whole FP out and start from scratch. Answer: First of all- fireplace flues should not be sealed at the top--even if you are installing vent-free logs. Vent-free logs are designed to place in a vented fireplace..and then you can use the damper open or closed.I suspect your fireplace is one of the metal pre-fab types- and the marble was glued on improperly...If a good construction adhesive was used (or silicone)- moisture would not be affecting it this way. Your problem probably has little to do with your capping of the flue.The smell- however could have something to do with capping the top---chimneys need to breathe and you have cut off the air flow. Heavy rains- high moisture- etc. combine with the soot and creosote left in the flue and cause a smell. The best remedy for this is to make sure the chimney is very clean..and purchase some of the fireplace deodorant available in local hearth shops.The fireplace glass door will do little to help your problems. Usually - air conditioning takes a lot of moisture out of the indoor air..can't figure why you'd have so much moisture.