Healthy Heat

Winter has arrived for those of us living in the northern hemisphere, and for most of us, that means the need to heat homes and other buildings has also arrived. Furnaces and other heating appliances can be a significant source of indoor air pollution, and heating methods can make a great deal of difference to the health of building occupants. In particular, any combustion inside a building (burning fuels like natural gas, propane, butane, oil, coal or wood) should be considered very carefully.

There are a wide range of pollutants produced by combustion. When a hydrocarbon fuel burns, each carbon atom should join with two atoms of oxygen and produce carbon dioxide ("di" meaning "two"). However, when oxygen levels are insufficient, carbon will join with one oxygen atom instead, and produce carbon monoxide ("mono" meaning "one"). Carbon monoxide can be very dangerous, but isn't the only problem associated with combustion.

Here are some things to consider when choosing a method of heating (including heating water and food as well as air):

• High levels of carbon monoxide can lead to convulsions or death, but low levels can cause symptoms that sufferers might not connect to exposure. In his book The Healthy House, author John Bower reports on a study that found nearly 24 percent of people who thought they had the flu were actually suffering low-level carbon monoxide poisoning.

• In the same book, Bower reports that more than 200 pollutants are present in wood smoke, some of which are carcinogenic. He notes that one study found 84 percent of children in wood-heated homes experienced at least one severe symptom of acute respiratory illness during the heating season, compared to only 3 percent in other homes.

• Maintenance and venting of combustion appliances is essential, but not enough to solve air quality problems. In the book Staying Well in a Toxic World,  Lynn Lawson states that California’s Lawrence Berkeley Laboratory found that carbon monoxide and nitrogen dioxide levels from a vented natural gas stove can become as high as those in Los Angeles during a smog attack. In an unvented room, the levels can rise to three times that amount.

• Carbon dioxide is not as dangerous to human health as carbon monoxide is, but elevated levels can be harmful in a number of ways. A recent study associated indoor carbon dioxide levels with impaired decision making. Carbon dioxide can build up even in buildings without combustion sources, because it is a product of human respiration. The buildup of carbon dioxide is one reason that adequate ventilation of a building is essential.

• Many people believe that combustion appliances are cheaper to operate than electric, but this may or may not be true. Electricity and fuel prices vary widely by location and fluctuate throughout the year. Electric appliances are also much more energy efficient than they once were. Electric heat pumps, although they can be more expensive to install than gas or oil heaters, are the cheapest heat source to operate, Prices vary based on local factors, but the authors of an FAQ page on heating estimate that in their area gas heating costs about 50% more than running an electric heat pump.

Heating methods are very important to indoor air quality and human health because the exposures are ongoing and continual. Combustion appliances also raise the risk of fire or explosion. Winter can be challenging enough. Let's not make it harder than it has to be.