Green Building Elements

Author’s note: the following article on home heating is the sixth in an eight-part series.

Metal woodstoves are a significant improvement over open fireplaces from the standpoint of producing more usable heat. They limit incoming air, thus avoiding heating air not needed for combustion. Another improvement: they use a lengthened heat exchange pathway to improve heat transfer from the heated combustion gases before they exit the chimney.

Unfortunately, metal woodstoves must operate at low, inefficient, and polluting combustion temperatures. Why? Because wood combustion requires high temperatures to be clean and efficient. Wood burns starts to burn cleanly at around 1200 degrees Fahrenheit, with continuous improvement up to about 2000 degrees. Cast iron begins to glow red and fail at about 1200 degrees. See the problem?

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Further, woodstoves don’t have enough mass to store the heat they produce. If installed in a house without lots of thermal mass, they heat only the air in the home, which can store very little of the heat. To compensate, woodstove users – like most fireplace users – opt for a slower, cooler fire that yields a modest amount of heat for longer. In doing this, they get less heat from their wood and send the rest, as smoke, up the chimney.

What about catalytic stoves? Catalytic metal wood stoves use clever tricks to raise combustion temperatures and lower particle emissions: brick-lined fireboxes protect the metal to permit somewhat higher burn temperatures, and catalytic converters reignite smoke at lower temperatures, for less pollution. However, since users of these stoves don’t necessarily have a way of buffering and storing heat, they frequently opt for the slow, dirty burn. This tends to foul the catalytic converter and produce pollution.

Lacking thermal mass for heat storage, and industrial-strength, high-temperature combustion chambers for efficient combustion, metal woodstoves are not optimal for whole-house heating in most homes.

The next article in this series will describe a relatively obscure, centuries-old appliance capable of producing clean, efficient wood heat: the masonry stove.

Previous Articles in this Series:

• Heating Your Home: Why Fireplaces Don’t Heat
• Heating Your Home: Thermal Mass
• Heating Your Home: Forced Air
• Heating Your Home: Heat 101
• Heating Your Home: Radiant Heat, Wood Heat

Photo credit: Linnell Esler via stock.xchng

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