Wood Burning = Green Heat?

February 26, 2007

Photo Credit: Heat-Kit.com
Heating your house with firewood is completely retro. I mean, cutting up trees and burning them, that’s just so old fashioned and inefficient, and not green at all.


What do you mean, wood burning can be green?

In fact, masonry heaters (which are also sometimes called “Finnish heaters” or “Russian heaters”) can be a green source for heating a home. While a traditional fireplace may be only 10% efficient (which is to say not!), a masonry heater can be 90% efficient. A well insulated house (even in a cold, Canadian location) can be heated on a single cord of wood per season. In a sense, a masonry heater is to a traditional fireplace what a compact fluorescent (or, even better, and LED light) is to an incandescent bulb.

The key, as is the case with passive solar heating, is thermal mass. When heating is taking place, you want to capture and store as much of that energy as you can, so that you can use it throughout the day. The masonry heater does this with a large structure containing a series of baffles, all of which gets heated up from a fast, hot-buring fire. By using a series of baffles in the structure, the heater ensures that most of the heat goes into the stone of the heater itself, rather than shooting up the chimney to be wasted, as is the case with a traditional fireplace.

Once heated, the thermal mass of the heater slowly radiates heat into the surrounding space over the course of a day. Because the heat radiates from the thermal mass in a straight line, spaces in direct line of sight to the heater are going to be better served than small closed-off rooms away from the heater. A masonry heater is not likely to be something that can easily be added to an existing home. The design of the entire house needs to be considered in order to get the best use from a masonry heater.

The carbon impact with this kind of wood burning is actually fairly benign. Firewood contains recently sequestered carbon, carbon removed from the atmosphere during the life of the tree. This carbon is re-released to the atmosphere when the wood is burned, where it can be reclaimed by other trees and plants. Fossil fuels, on the other hand, have had their carbon sequestered for millions of years. By burning fast and hot, the masonry heater produces less of the soot, creosote and other by-products that are formed when a fire smolders and burns slowly. This makes it less polluting as well as more efficient.

A masonry heater doesn’t make sense for every location (nor does any other technology). It would make no sense to have one in a city where the firewood needed to be trucked in from a distant source. But for a location where firewood is a readily available local resource, it can be worth considering. And with a masonry heater, burning wood can be a green heating method.

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