What about supplying outside air to my wood stove?
I first learned about outside air kits when I was about to close a sale with a customer who lived in a mobile home. One of the more experienced salesmen in the store I had recently become the manager of, warned me that the requirements for mobile homes were different. “You need double wall connector, the stove has to be bolted to the floor, it has to be grounded to the chassis, and you need outside air.” He said. I can’t remember with absolute clarity but I’m sure I wondered why if the people in the house could breath the stove needed help. But I moved on, and in the hectic hearth store atmosphere accepted outside air as something that was necessary when installing a stove in a “tight” home. I was a little confused about fixing the stove to the floor too, did HUD think these mobile homes actually moved after they were delivered. Maybe they thought it would hold the stove in place in case a tornado came by.
Some time later outside air reared it’s now ugly head at Jotul. The more I learned about it the more I realized it was not a solution based in good science. There are a couple of schools of thought on outside air. Some think that because the air from outside is used for combustion instead of the heated indoor air there is an efficiency gain. There would be a grain of truth in this theory if there were not copious amounts of air flowing in and out of the house at infiltration and exfiltration points. If houses were truly as efficient as they are billed they would not cool down so quickly when the heat was turned off! Which leads me to the second theory. This camp thinks that some houses are so air tight that the naturally drafting stove will remove too much air from the house. If they are that tight there will be much more serious problems like mold and I don’t even want to go there. If a house is built with double vapor barriers, sealed outlets and fixtures, sealed sills, and a super insulated envelope then an air-to-air heat exchanger is a must to ensure the health of the occupants. This engineered system can be calibrated to compensate for any appliance that will remove air from the house, not just the wood stove.
An excellent source of information on the subject I found is the non-commercial web site www.woodheat.org. This is an informational site that has tons of great information for wood burners or people who want to burn wood. It was at a seminar given by one of the founders of the site that I watched a very disturbing video of “outside air gone wrong”. The video showed a zero clearance wood-burning fireplace that had an outside air “inlet” connected to it. There was a strong wind blowing and the inlet was located on the leeward or downwind side of the house. The wind was blowing across the top of the chimney creating a zone of positive pressure. There was also an area of negative pressure on the side of the house where the “inlet” terminated. Since areas of high pressure flow to areas of low pressure the combustion air was coming down the chimney and the exhaust was flowing out the “inlet”. The inlet is not designed to safely contain the heat or by-products of incomplete combustion so this installation could lead to a disastrous result.
Until we are proven wrong with science the air for a naturally vented appliance should come from the room the stove is in. Speaking of science apparently it has been applied to the notion of outside air for wood burning appliances in Canada. Research shows that the design of the stove, chimney, and house as a system has much more to do with successful venting than outside air. There are of course codes that contradict this point of view and in these cases the code should be followed in accordance with a ruling from “The Local Authority Having Jurisdiction”. Perhaps the institutions that are responsible for these codes will catch up with the times. We can only hope this will happen soon!