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Use boiler for hot water


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Not for heating, but way back when, I used a copper coil in a woodstove to heat water in a converted tank behind my stove. I kept the electric element in the upper section of the tank for a backup to keep the water hot overnight and such. Keep in mind that the water circulating in the coil cools the stove down to some extent, so you need to burn a hotter fire to prevent creosote buildup. The old woodburning cookstoves had a cast iron jacket that sat alongside the fire box for water heating and that worked real well, better than a thin coil.

Here are some pics of a very well built woodburning boiler. The fellow who built this was a real craftsman. This system uses hot water radiators/convectors and was keeping a 2000 sq ft home warm in January on the electric backup heater alone.

The chimney had some serious creosote problems. I suspect the old timer hadn't been there to make sure there was dry wood and a hot fire.

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A few years ago, I did a home here in Seattle for an elderly widow of deceased Boeing engineer. The home had originally been heated with hydronic floor heat and had used three different heat sources - a gas boiler; a woodstove equipped with a coil heat exchanger in the back of the firebox, and a rooftop solar water heater.

There was a very large (100 gallon) storage tank on the system. Inside the storage tank was a coil heat exchanger that was plumbed to a circulator and to the solar water heater on the roof. On sunny days they could use the solar water heater as the heat source; on cloudy days, and we see a lot of those, they were able to build a fire in the woodstove and use the woodstove to heat the water with the heat exchanger at the back of the firebox; and year-round, regardless of weather, they were able to use the gas boiler to heat the house.

Next to the large storage tank was a gas water heater with an immersed coil. A circulator between the two tanks cycled water from the storage tank into the immersed coil so that they were able to heat water with either the gas water heater, the solar system or the woodstove.

Apparently, after he died, the system had been too complicated for the widow. During the non-heating season she had to isolate it from the floor heat so that she could still heat water with the solar hot water heater and/or the woodstove at nights or when it wasn't too hot. At some point, she'd thrown in the towel and had installed electric baseboard heaters throughout the house. I found the pipes cut off the back of the woodstove with caps soldered over their ends; the pipes leading to the solar water heater were also disconnected and the floor coils had been disconnected and drained years ago.



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