Burning wood seems, intuitively, the environmentally friendly choice. After all, it's a natural and renewable resource, and people have been burning wood for hundreds of thousands of years.

In fact, woodsmoke is almost always more harmful than emissions from an oil or propane appliance, says Pat Paslawski of Yukon Renewable Resources' Environmental Protection and Assessment Branch.

"Commercial fuels are pure hydrocarbons, which will burn completely to produce water, carbon dioxide, and only very small amounts of pollutants and ash," Paslawski says. "Even when burned properly, wood produces a much greater amount of small airborne particles, or particulates, that can clog up our lungs and harm plants."

"The new generation of high-efficiency wood stoves and pellet stoves are much cleaner, though," he adds.

The problem with wood is its chemical complexity. Pure hydrocarbons like methane, ethane, propane, and butane combine with oxygen when they burn and produce carbon dioxide and water in gas form, Paslawski explains.

However, living matter, like wood, is composed of a great variety of organic molecules. Some of them will burn and some won't, and the molecules that burn do so at a variety of temperatures. As a result, a fire hot enough to burn some components of wood will leave other compounds unconsumed and free to drift away in smoke or clog up the chimney as creosote.

The smoke produced by burning wood is a major danger to human health, Paslawski says. The smallest woodsmoke particles pass through the body's defenses in the nose and throat, and penetrate deep into the lungs. And among those particles are many carcinogens, compounds that can cause cancer.

Woodsmoke can also cause milder health problems, such as sore throats, coughs, runny noses, headaches, and nausea, even in healthy adults. In children, the elderly, or people with allergies and heart or lung conditions, the effects can be serious.

Studies in a number of places link increasing levels of woodsmoke with increases in school absenteeism, emergency room visits, asthma attacks, and a variety of other health problems.

To avoid health problems, it's important to burn wood as cleanly as possible, says Paslawski.

"The cleanest burns are quick and hot," he says.

The recipe for a clean-burning fire is to start the fire with small pieces of dry kindling, burn only dry, well-seasoned wood, avoid overloading the stove, and leave the damper open so that the stove burns hot.

Damping down the fire will keep it burning for hours, but smoldering fires send more unburnt wood energy up the chimney and create more woodsmoke, Paslawski says. They also lead to creosote build-up in the chimney, which can cause a chimney or house fire.

Burning green wood, treated wood products or garbage in a woodstove can result in a cooler burning fire and may release toxic gases.

"If you have a woodstove, it best to have a backup, fuel-fired system that can kick in when you are gone for a long time," says Paslawski.

Regardless of your heat source, the best solution is an energy-efficient house. If your house is well-insulated, you should be able to leave for the day and return to find it still comfortable, if not exactly cozy.

"You will save money over the long run by investing in some insulation and weather-stripping," says Paslawski. "You won't spend so much money on heating the great outdoors!"

For more information about burning wood cleanly and the effects of woodsmoke, contact the Environmental Protection and Assessment Branch, Yukon Department of Renewable Resources, at 667-5683, or by e-mail at environment@gov.yk.ca.