Is burning wood for heat an efficient and renewable way to keep our homes warm—or a dirty relic that pollutes air and ruins habitat?
Wood straddles the line between being a renewable and a fossil fuel. It is a store of solar energy and atmospheric carbon that can be consumed at a pace similar to the rate at which it is produced—in which case it is renewable. Or it can be burned more quickly, acting more like a fossil fuel. Unlike with vehicles or other complex energy systems, pollution from wood heat remains largely unregulated, and there’s a high potential for misuse. That’s reason to become better informed about the technology and how—and when—to use it most efficiently.
There are many reasons why burning with wood can be appealing. First, trees can regenerate or be replanted, making wood a potentially renewable fuel. Trees also consume carbon dioxide (CO2) so, over time, heating with wood has the potential to be carbon-neutral. In places where there is little solar gain to be had in winter, wood offers an opportunity to use stored solar energy to provide heat.
Heating with wood can make you more energy-aware. Even if you have already-split wood delivered, using wood and turning it into energy requires forethought and effort—carrying, splitting kindling, and stacking. This is very different than simply adjusting the thermostat and writing a check to the utility once a month. Also, if the appliance is thoughtfully placed to heat commonly occupied spaces, wood heat can reduce the overall amount of energy consumed for space heating compared to a typical furnace system, which supplies heat to all of the rooms in the house, all the time.
For those on a budget, wood heat has the potential to save money compared with other fuel systems. And wood heat often means independence—both from power outages and the vagaries of the market, especially if you can harvest wood from your property. If wood is purchased locally, it can also help keep dollars in the community.
But the way we’ve burned wood for most of human history—in open hearths—is dangerous, inefficient, and polluting. And even efficient modern wood heaters have drawbacks, so they need to be used responsibly and appropriately. For instance, harvesting trees for firewood can turn into decimating forests if it’s done on too large of a scale. Estimates by wood heat advocates are that an acre of healthy forest can produce a half-cord (64 cubic feet) of split wood each year. Obtaining wood from smaller companies that get most of their wood from tree-trimming or forest management can provide a sustainable source. Source your wood (whether pellet or cordwood) from a company that is not engaged in clear-cutting or shipping wood long distances, which consumes lots of fossil fuel.
Burning wood can produce a large quantity of airborne pollution, especially if done inefficiently. According to the U.S. Environmental Protection Agency (EPA), burning improperly cured wood is the biggest contributor to airborne pollutants from wood-burning heaters. Properly cured wood has a moisture level of less than 20%. Typically, this is achieved by air-drying rain-protected split wood for at least six warm months. Properly seasoned wood has more than four times the heat value of green (uncured) wood, since, when burned, not as much energy has to be used to remove moisture. Then there’s the efficiency of the fire, which needs to get hot enough (around 1,000°F) to completely combust the material. This requires advanced wood heater technology, which most modern wood heaters have.