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.

I started making custom woodstoves and fireplace inserts in the seventies and made hundreds of custom units with the help of up to seventeen employes. These units were developed to be very efficient and clean burning. In fact they were considered by experienced customers to be better than the best factory made units available on the market in terms of burning with a clear exhaust and no smoke. The Washington state wood stove emision law, however, was designed to put all custom manufacturers and small manufacturers out of business, which was greatly appreciated by the large manufacturing companies.

I started up again in my garage and started specializing in custom fireplace doors. We had made some of these doorsets before in the woodstove shop and they were essentially like the front end of a heavy duty, high efficiency, fireplace insert which was enlarged to maximise the glass area. Really, all the important parts of most high efficiency woodstoves were on the front end and the rest of the units were basically just big heavy steel boxes. If you have a masonry fireplace inside your home you don't really need the steel box anyway.

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.

The Way they work

Wood burning doorsets all have an airwash at the top of the door. The draft (suction) provided by the hot air rising up the chimney pulls air into the adjustable air valves which are located above the door and then into the air wash, which directs a thin curtain of air down against the glass. This curtain of air next to the glass helps to keep the glass clean as it descends down to the fireplace floor, where it feeds the base of the fire. Some air also peels off succesively at higher levels and this feeds the top of the fire and burns the smoke, which is called secondary combustion. Airwashes and secondary combustion is what high efficiency woodstoves are all about, and now you can get the same benefits in a fireplace doorset.

Using this feature and dry wood you can easily burn your fireplace so that the chimney gives off no smoke or visible exhaust, which is the neighborly thing to do and is visual verification that you are getting maximum heating efficiency from your fireplace.

Another way that these doors heat is that they limit the amount of heat going out of the house up the chimney. In open fireplaces 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.

This is a simplified drawing representing a heating doorset in a masonry fireplace. Side view. Cross section. Arrows show the path of the air as it enters the air valves (bright red) and is then deflected by the air wash, (brown) so that it goes down through a narrow slot between the bottom of the air wash and the glass (yellow). It shows how a curtain of fresh air sticks to the glass and then goes down to the floor of the fireplace where it feeds the fire. Some of the air peels off at higher levels, which feeds the top of the fire.

Gas logs in fireplaces

Gas logs are notorious for wasting large amounts of gas when used in a typical open fireplace so putting airtight doors on a fireplace that has gas logs will heat your home 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. Since gas burns pretty cleanly there is no need for the upper air valves and air wash, they work well with the simpler and lower profile lower air valves.

Neoceram Glass

Some heating units should get neoceram glass, for detailed advice on whether or not to select the optional expensive neoceram glass, rather than the standard tempered glass, for your doors please click here: Neoceram glass

Masonry fireplaces only

I make fireplace doors for masonry fireplaces only and do not make fireplace doors for or install fireplace doors in metal fireplaces, which are often called zero clearance fireplaces or tin can fireplaces by builders. Metal fireplaces frequently have masonry slabs lining the inside of the firebox, so if you are unsure about whether or not you have a masonry or metal fireplace you can tell by going outside your house and looking at the chimney above the roofline. If it is solid brick or stone then you have a masonry fireplace, if it is a wood box (even if it has a fake brick veneer covering) with a metal cap sticking out of the top then you have a metal fireplace.

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