I have a 4 yr old home with a propane gas insert fireplace on an exterior wall. It direct vents from back of insert out through the wall, that has a buildout for the fireplace. My problem is the glass front on the fireplace has condensation on it all summer and I have gone through two sets of logs deteriorating from the moisture in the fireplace. Several of my neighbors have the exact same fireplace but no problem with condensation on inside of fireplace. What could be causing the problem?