Posted by Karen Duke on 11/6/2017 to Tech
We got another e-mail today from a homeowner inquiring about using a vent free (unvented, ventless) gas appliance in her unlined chimney. This comes up often and I thought it was a good topic to share.
Hello, We are wondering if you sell vent-free gas fireplaces. We have an old home and the chimney is not in good shape to be used for a vented fireplace. I believe there originally was a ceramic radiant heat insert in the fireplace opening. We are trying to find a small vent free insert for that space, and we are not having much success. Thank you. - Delia
We don't recommend vent-free models for several safety and performance reasons. First, they emit high levels of moisture; for every gallon of gas they consume they are emitting virtually a gallon of moisture. Coal soot is high in sulfur and in a dry chimney causes slow deterioration, but the moisture from the vent-free turns that sulfur into sulfuric acid which can rapidly deteriorate the bricks and the mortar that holds them together. This results in a condition that can lead to the chimney caving in and causing all kinds of structural problems. Old houses don't have a damper that can close so the moisture is going to go up the chimney.
Second is the fumes they produce. Vent-free means these gas appliances don't have to be vented up the chimney so if you choose to block off the chimney then the fumes are vented into your living space. Vent free should never be used if anyone in the house is pregnant, asthmatic, anemic, diabetic or has any kind of heart or respiratory problems. Again, that moisture is a problem inside your house, especially in the winter when the doors are not opening often enough to let fresh outdoor air into your home. The excess moisture often leads to mold and mildew problems which in turn irritates respiratory conditions such as asthma and allergies. And any time you burn gas you are producing carbon monoxide so that is coming into your room too. Diabetics and those with heart conditions and lung diseases will find them intolerable. I'm diabetic and vent-frees rapidly cause me to become dizzy, nauseous and confused.
I acknowledge that they don't affect everyone this way, but it's hard to recommend them when I know they make me sick. We sold vent-frees when they first came out in about 1993 and I got a case of the flu that wouldn't go away. I went to my doctor a couple of times, then asked him if he'd test me for carbon monoxide poisoning. The results showed I did indeed have low level carbon monoxide poisoning, which is significant because leaving the building should have infused me with enough oxygen for the carbon monoxide to have left me by the time I drove to the doctor, waited for them to draw blood, etc.
My honest recommendation is to consider a vented gas insert, which includes a chimney liner to carry away those fumes safely, or for a less expensive alternative that you consider an electric fire. The electrics produce enough heat for a room approximately 12' x 16'; they don't smell bad and offer a pretty little flame.