The House Detective by Barry Stone, Certified Home Inspector
Dear Barry: We built a new home and installed a ventless gas log fireplace. As we look back, this seems to have been a stupid mistake. Since using the fireplace, a film has been forming on our windows. Our suspicion is that it is caused by exhaust from the ventless fireplace. What must it be doing to the air we breathe? It is too late to add a vent? Deborah
Dear Deborah: Installing a ventless gas log fireplace may have been an “unfortunate mistake,” not a “stupid” one. Most homebuyers, having limited esoteric knowledge of gas fixtures, would have no reason to suspect that a fully approved gas fixture such as this could be problematic or potentially unsafe.
The film on your windows may in fact be a combustion byproduct, and this, as you suspect, could be unsafe to breathe. Until this can be evaluated by a licensed expert or by the gas company, use of the fixture should be suspended, and the pilot (if there is one) should be turned off.
Ventless gas fireplaces operate without a chimney to the exterior of the building. They are designed to produce combustion products that are safe to breathe and can thus be vented directly into the home. The guaranteed safety of these fireplaces has been a subject of ongoing debate between product manufacturers and other experts in the fireplace profession.
The general claim of manufacturers is that ventless gas fireplaces have been designed in such a way that they will automatically shut down in the event of any combustion or venting problem. The opposing view is that regardless of built-in safeguards, there is no such thing in the realm of human invention as a 100% failsafe device. Failure may be extremely unlikely, but it can never be deemed as impossible. When one considers the potential consequences of venting partially burned gas into a home (i.e. carbon monoxide), nothing less than “impossible” should suffice as an acceptable criterion.
Adding a vent to the existing ventless system is probably not possible. Therefore, replacement with a different type of system (such as a pellet stove) may be a prudent alternative.