Fires in open hearths, and in older wood stoves and fireplace inserts (generally pre-1991) that do not employ advanced stove technology are not able to reach sufficient temperatures to combust the gases and soot that burning wood creates. This means they are inefficient, letting much of the potential fuel “go up in smoke,” and they are polluting, because that smoke permeates the air in the surrounding neighborhood (and with open hearth fires, in your home), potentially contributing to health problems such as asthma and lung disease.
But even well-cured wood burned in an efficient wood heater produces pollution. Most smoke from a well-built fire is CO2 mixed with carbon monoxide (CO), but trace amounts of potentially lung-damaging particulates such as dioxins and volatile organic compounds, and heavy metals such as arsenic are found in wood smoke. Like car exhaust, the key to reducing any potential harm from the results of this combustion is dispersal. Some regions have atmospheric inversions in winter that can trap pollutants at ground level for days. Population density also has a dramatic effect on particulate pollution from wood heating. Where burning wood displaces direct combustion of fossil fuels—like with oil- or natural gas furnaces—the pollution level increases substantially, often 100-fold or more. There is a trade-off between burning wood, a potentially renewable fuel that creates more particulate but less CO2 pollution, versus burning a fossil fuel-based system that creates fewer particulates, but more CO2 pollution.
So when is heating with wood an appropriate solution, both economically and environmentally? Five factors come into play:
Although heaters are rated on their output (in Btu per hour), the range can be quite large and depends on several factors, including the species of wood, the moisture content in the wood, and how the heater is operated. An “average” U.S. home can require 25 to 30 Btu per square foot per hour to maintain comfortable temperatures, says Consumer Reports magazine, but there’s really no “average.” Your home’s size, layout, and insulation determine how easy (or difficult) it is to heat. A better way to “size” a wood heater is to figure out your home’s heating requirements, either through analyzing previous heating bills or performing a heating-load calculation. Speaking with a nearby dealer (who heats his or her home with wood) is usually the best way to get a properly sized, quality wood heater.
Once you’ve determined you want to heat with wood, there are several types of wood-burning appliances to consider. Your choice will depend on your home’s specific heating needs.
Metal heaters (aka wood stoves). Technological improvements in metal-constructed wood-burning heaters include insulated fireboxes; a means for secondary combustion; and catalytic converters, though not all heaters will have all three. An insulated firebox, usually insulated with rock wool and/or insulating firebrick, is the first strategy toward an improved burn since it can contain the heat better, raising the fire’s temperature. The hotter the fire is, the more complete the combustion will be, resulting in higher efficiency and lower emissions. Improved sealing and insulation of the firebox (usually with high-temperature silicone) will be reflected in the metal heater’s efficiency numbers.