Be aware of old wood stoves. They are very inefficient and pollutant and they use too much wood; they emit many toxic pollutants that are a cause of serious health problems, namely in people with asthma or heart problems.
Even occasional exposure to wood smoke can be very harmful to our health. Be careful to symptoms like stuffy noses, chest tightness or watery eyes.
And do not forget the serious air pollution problems that they may cause in valleys and areas, where geography helps to trap air pollution.
New heating stoves
Fortunately, new stoves can overcome most of these effects. They are much more energy-efficient and they have very low emissions. Their technology has improved immensely over the last decades.
The efficiency of the best new wood stoves is now about 80% or more (four or five times the efficiency of older models) and their emissions are now reduced to 2,5 grams per hour for catalytic stoves and to 4,5g/h for non-catalytic units in many jurisdictions (traditional wood stoves have an average emission of 15-30 grams per hour).
Be cautious anyway. Take into account the disadvantages of wood heating and stoves. There are cleaner and more effective alternatives for energy-efficiency. Gas stoves can be one of them: they allow an easy control of the heat output, and are cleaner and cheaper. See: Gas Stoves Energy Efficiency.
Qualified wood stoves
If shopping for a wood stove, look for a qualified unit. That’s a guarantee of quality, efficiency and safety, and it's easy to identify them in the USA and Canada, where they have an EPA white label on their back, and a hang tag (image at right).
When comparing wood stove models, look for their certification and pay close attention to their emissions, knowing that a lower grams/hour rating means a cleaner and more energy-efficient unit.
For a list of qualified stoves (and stove manufacturers), see: Current list of EPA-certified wood stoves (PDF).
You may also look for the safety labels of certification bodies like UL and ULC.
Wood stove technology
Modern wood stoves belong to two technological groups: the non-catalytic and the catalytic stoves.
Catalytic stoves use a catalyst, that is, a coated ceramic honeycomb, able to capture and to burn smoke gases. They require more maintenance and the catalysts may not last as long as manufacturers claimed.
Most of the advanced wood stoves on the market are non-catalytic. They use a secondary combustion air system to burn the pollutants and to increase their efficiency; they are typically easier to maintain, and cheaper.
Wood stoves come in different capacities, and you should consider the issue carefully. Oversizing is very common, and a recurrent problem.
If you have a highly insulated home – or if you plan to air seal and insulate it to very high levels, for energy efficiency – wood stoves are a poor choice. It’s very difficult to control their heat output to the required levels. Even small stoves, intended to heat just a single room or part of the house (zone heating) can be inadequate. And that makes gas stoves or direct vent wall gas heaters a much better choice.