Wood Stoves Need Air Too
There is plenty of information in the code books on installing and operating oil- and gas-fired appliances, but much less on wood stoves. Instead, codes often defer to the stove manufacturer’s instructions for safe installation and performance. In Fairbanks, not only do the wood stoves vary greatly but so do the conditions in homes where they will be operated. We see everything from barrel stoves and custom-welded fireboxes on up to factory-built sealed-combustion systems with catalytic converters. We also have some of the some of the tightest homes in the world and periods of extreme cold that are capable of creating large air pressure differences between indoors and outdoors, and also between different levels inside the house. This all affects how your stove operates and the health of your indoor air.
With so many variables, the bottom line is that ALL fuel burning appliances must have an adequate air supply to burn safely and efficiently. In a tight house, it’s also critical all exhaust appliances have an adequate supply of air. To operate safely, a house must be able to withstand a “worst-case draft test.” This means that when all exhaust fans in the home are running at the same time, they cannot create enough negative pressure to backdraft harmful gases from any combustion appliance into the home, including the wood stove. Often backdrafting from a wood stove is noticeable, but not always, and carbon monoxide in the exhaust is odorless and colorless.
Local codes are very clear that if a home contains a fuel-burning appliance, a carbon monoxide detector must be installed: “Where a fuel-fired appliance is installed or replaced in an existing dwelling and approved carbon monoxide alarm shall be installed outside of each separate sleeping area in the immediate vicinity of the bedrooms.” Many high-efficiency wood stoves include provisions to install direct vent combustion air kits; this involves installing ducting from the stove to the outside, since combustion air is assumed to be outdoors. If the air supply isn’t directly attached to the stove (per manufacturer instructions), then it should be within the same air space shared by the stove, not in another part of the house separated by a door. You may also want a mechanism to open and close the air supply so cold air isn’t pouring into the home when the stove isn’t operating.
The chimney is another important factor in wood stove combustion. If it’s not sufficiently insulated and lower than the top level of the home’s conditioned space, backdrafting is likely to occur even if the stove has adequate combustion air. Wood stoves in the basement of a multi-story house are particularly susceptible to this problem. Opening a nearby door or window until a strong draft is established is a common and temporary solution.
If you have any questions regarding combustion air, consult an engineer, certified stove installer, or certified chimney sweep, who can help design a supply air system and chimney to make sure your house is safe.