How to Choose a Wood Stove
Design & Installation
Smoke is generated by incomplete combustion, which can be caused by lack of oxygen, low burning temperature, wet or green wood and other factors. Generally, any wood stove design feature that has been proven to promote more complete combustion is desirable. These features include insulated baffles, heated primary and secondary air, firebox insulation and advanced designs that promote secondary combustion.
Baffles
If combustion gases go up your chimney without being fully burned much of the energy in your firewood is wasted. Baffles increase the efficiency of your stove by increasing turbulence. They hold the gases inside the firebox longer, directing them back into the fire so they will burn more fully and make the fire burn hotter. An insulated baffle keeps the temperature of the gases high to promote this secondary burning.
Air Supply
Inside the stove, pipes or channels allow preheating of the primary and secondary air which can mix with the smoke and ignite to give secondary combustion and ensure that combustion is more complete.
Firebox
Firebox insulation (such as firebrick) stores heat and keeps the combustion temperature high and stable. Heat storage warms your home long after the fire is out; a consistently high firebox temperature promotes more complete combustion.
Certification and Emission Standards
The Canadian Standards Association (CSA) has developed an emission standard (CSA B415) for wood stoves, inserts and small fireplaces. This standard recommends that emission levels of wood stoves manufactured in Canada meet requirements equivalent to the standards of the US Environmental Protection Agency (EPA) (1990). Many of the stoves manufactured in BC are also sold in the US, and already meet EPA emission standards.
In the United States, wood stoves have been regulated for some time by the EPA. Stoves must be tested, and their emissions monitored, to determine the level of particulates they produce. Stoves cannot be sold to the public unless their particulate levels meet the EPA emission standard. Certified stoves can reduce smoke emissions by as much as 90% compared to conventional stoves, and are much more efficient. If your existing stove is more than 7 years old consider getting one of the new advanced combustion units. You won't regret it.
These certified stoves often include design features that promote secondary combustion. Most of these features are aimed at burning off the dangerous chemicals and toxic substances before they leave the firebox. This is achieved when 1) the fire has an adequate oxygen supply, 2) the gases coming off the fire are at high temperature and are mixed with preheated air (oxygen), and 3) the gases have enough time to burn before they cool down.
Wood Stove Technologies
There are many different stove designs, but most fall into 3 basic technologies: advanced combustion, catalytic combustion, and densified pellet combustion.
Advanced Combustion Stoves
Advanced combustion systems create the conditions necessary to burn combustible gases. Their features include:
- Firebox lining that keeps temperatures high;
- Devices that deflect gases back into the flames so that they burn more completely; and
- Heated secondary air supplies that ensure that enough oxygen is present and the temperature remains high.
Canadian manufacturers, including BC companies, have established an international reputation as designers of some of the most effective advanced combustion appliances in the world.
Catalytic Stoves
A catalyst is a substance that affects a reaction without being consumed in the process. In wood-burning stoves, exhaust gases can be routed through a catalytic combuster - a ceramic honeycomb coated with a metal such as platinum or palladium. Smoke gases and particles pass through the combuster and ignite at a much lower temperature (250°C) than they would without the combuster (500°C). The result is that harmful substances are more completely burned. The fuel produces more heat through an extended clean burn. However, catalysts can deteriorate over time and must be replaced.
Pellet Stoves
Wood pellets are made of wood byproducts that are dried and compressed into cylinders 25mm long by 6 mm thick (one inch by a quarter-inch). Pellet stoves include a hopper to hold the fuel and a screw auger (usually electric) to move the pellets from the hopper into the combustion chamber. Pellets usually burn cleanly because they're fed to the combustion chamber at a controlled rate and are matched with the right amount of air to maintain an optimum burn rate. That's why they have the potential to operate at significantly lower emission levels than cordwood stoves.
Most pellet stove designs require electricity to operate their fans and auger motors. Therefore, they do not operate during a power failure. They tend to cost more than wood stoves and they need regular service. But they have advantages over cord wood stoves, in addition to significantly lower emission levels: easy loading, convenient, automatic operation, and precise control over heat production.
Safe Installation
All wood-burning stoves must be properly installed to be safe and efficient. Follow the manufacturer's instructions on clearances and connections. Make certain the installation conforms with BC building codes, local requirements, CSA safety standards and local fire safety codes. Ensure that the chimney system is the proper size and is approved. Consult your fire department or building inspector before installing any wood heating unit and chimney system.
