We live in mid-Michigan, and a few years back we had an 8′ x 10′ year-round leisure room built onto our home. The house wall was drywalled and painted, and the three outside walls have slider windows and a set of patio doors. We installed a ventless natural gas wall heater and added a wood enclosure to give it a fireplace look. In the winter months, we have a problem with the room “sweating” and dripping onto our furniture from the ceiling. Do you have any suggestions for us?
Ventless is the key word behind the moisture problem in this room. Natural gas is 80 percent water vapor, and when that vapor doesn't have a proper escape route, it creates an indoor environment akin to a tropical rainforest and extends a direct invitation to dangerous molds and bacteria.
The heater may be called ventless, but that only refers to the fact that it does have a vent pipe taking all that moisture outside. In actual fact, the gas heater is venting inside your house.
I recommend replacing your existing ventless natural gas heater with a vented gas fireplace. That way, you'll have the comfort you need, the good looks of a traditional fireplace, and a safe, dry room to enjoy.