The first customer to order one of the heating doorsets came back later and told me the following story. During the first day his wife had burned it like a regular open fireplace, at full throttle and burning wood at the same rate as they had done with the open fireplace. That evening it was eighty degrees in the house, with all the doors and windows open, in the winter, and they sat around in shorts, drinking iced tea, trying to stay cool.

The Way they work

The way that these doors heat is that they limit the amount of heat going out of the house up the chimney. In open fireplaces with no doors the chimney pulls so much heat out of the house, which pulls cold air into the house, that the furnace normally must come on to replace the lost heat. The small outside air supplies provided with many of the newer fireplaces are much too small to make up for all the air that is sucked out of the house so the result is that cold air gets pulled in through doors and windows, which cools your house off. Open fireplaces can make you feel warm when you sit in front of them due to the radiant heat, but ultimately most of the heat goes up the chimney and many open fireplaces have a net cooling effect on a home. When you put air valves on the doors you then have a throttle for controling the fire and you greatly limit the amount of heat going out the chimney.

The large amount of cool air that is pulled into a fireplace that has no doors will keep the fireplace masonry itself from getting very hot. When you eliminate the cooling effect of excess room air entry with airtight doors the heat gets a chance to really soak into the masonry and the entire fireplace and chimney gets much hotter. This does two things, the much hotter fireplace causes the fire itself to burn hotter, which makes it more efficient, and when the fire dies down or you go to bed in the evening you close the air valves which keeps cool air out of the fireplace and chimney, and this large amount of heat stored in the masonry will stay in the house and continue to heat your home through the night. Due to this heat storage in the masonry, these doorsets provide a benefit that modern fireplace inserts do not provide because they shield the masonry from most of the heat.

What happens when you put one of these doors on a wood burning masonry fireplace is that you are turning your fireplace into a giant high efficiency woodstove which in most cases is big enough to heat a pretty big building.

Gas logs in fireplaces

Gas logs are notorious for wasting large amounts of gas when used in a typical open fireplace so putting fireplace doors on a fireplace that has gas logs will heat your home efficiently in a manner similar to wood burning units. Gas logs don't put out as much BTUs as a wood fire can, but gas can help make up for that by providing a steadier heat output.

Masonry fireplaces only

I prefer to install doors into masonry fireplaces only and not install them into metal fireplaces, which are often called zero clearance fireplaces or tin can fireplaces by builders, but most chimney sweeps can do professional installations for you.

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