I have to disagree with your published opinion that outdoor wood boilers are an environmentally sound way to heat. While they do move the fire, soot and ash outdoors, they also burn twice as much fuel as an indoor woodstove due to heat loss from the boiler to the home. Also, a piece of firewood that would take five or ten years to decompose is converted to ash in a half-hour. This is compounded by the removal of living trees from the forest that would have helped absorb greenhouse carbon dioxide in the air had they not been cut down. How can you say that heating with a wood-fired outdoor boiler is a green option?
An outdoor wood boiler is a freestanding unit that heats water before it’s circulated into a building through insulated, underground pipes. The hot water moves through radiators or infloor heating pipes to warm one or more buildings. And you’re right about some outdoor boilers using a lot of wood, though that’s a matter of design. Today’s best models include lots of heat-exchange passages to extract almost all the heat from the exhaust stream before it leaves the boiler. The model’s I’ve researched use 75% less wood than average, they emit virtually no smoke and are independently tested to operate at least 90% cleaner than traditional boilers.
As far as greenhouse gases go, a properly harvested forest grows more vigorously than an mature one, removing more carbon from the atmosphere as a result. Forests can be poorly managed, yes, but in many parts of Canada it’s possible to heat with wood while rarely cutting a live tree. I’ve done it at my place for 20 years. I can’t even begin to keep up with the trees removed incidentally to clear land for other uses, or those blown down in wind storms or cut by beavers. The best insulated pipes that deliver hot water to buildings for heating are also very efficient. They only lose about 0.5ºC over a 70 metre run.
Although heating with wood doesn’t always offer environmental benefits, it certainly can. Burning natural gas or oil (or using fossil fuel-generated electricity) always results in greenhouse gas emissions, no matter how cleanly these fuels are burned. Fossil fuels are also expensive enough to cause hardships, and they make our economy susceptible to political unrest on the other side of the world.
Wood heating isn’t the answer for everyone, but in the right circumstances, done in the right way, it’s definitely part of a green way to live, especially here in Canada. Scandinavian countries are way ahead of us in the greenhouse gas issue, and many of them use wood heating extensively, even in urban situations where wood pellets are burned for domestic and industrial uses.