I was surprised when I read through Matthew Teague’s interesting article in the Oct/Nov issue. There is not much about combustion air for wood burning stoves and where it can come from, inside the house or outside the house. He does mention the expense of all the internal house air being consumed to burn wood to supplement home heating but no mention of the danger of burning inside air.
Every fall and winter there are reports about people burning their woodstoves or wood fireplaces either for that warm cozy beside the fireplace feeling or to supplement house heating who wind up in the hospital close to death because the woodburning combustion air comes from inside the house.
I have a woodstove that I use for supplemental heat but it is described as an airtight that burns only air from outside the house, it does not burn inside the house air. It is capable of heating my two story 1300sq ft cabin by itself. As it gets colder outside, we burn more wood faster.
There is a fan that blows heated air away from our stove and we also use a ceiling fan to help circulate heated air. These fans do help and I recommend their use.
I hope anyone contemplating the purchase of any wood burning appliance for their home bases their decision on a lot more than just this article. It is possible to go down to the local building supply store and purchase one with all the required chimney connections.
Ed
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In the Pacific Northwest where tight energy efficient houses were required by energy building codes, I recall that there had to be a specific provision for combustion air for wood stoves (and other combustion appliances). I recall that the wood stove either have a direct connection w/ combustion air from the outside or that air be supplied in the immediate vicinity of the device. I also recall some discussions that people were restricted in making a direct connection on a device not designed for it ... as it would void the U-L rating (by altering the device).
In older construction, this isn't much of an issue. But with the newer energy efficient construction techniques, this becomes an important thing. Not sure what the newer energy codes say about this type of thing (the International series). You should not treat it casually, though.
>>>Every fall and winter there are reports about people burning their woodstoves or wood fireplaces either for that warm cozy beside the fireplace feeling or to supplement house heating who wind up in the hospital close to death because the woodburning combustion air comes from inside the house.
I have never heard of such a story. Do you have any references?
On the other hand, this article poses some interesting thoughts on the 'myth' of outdoor air supply:
http://woodheat.org/outdoorair/outdoorairmyth.htm
Scott.
Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.â€
Interesting read. I notice however that there is no real documentation of the claims made in the article.
They can't get your Goat if you don't tell them where it is hidden.
>>>I notice however that there is no real documentation of the claims made in the article.Yes, I agree. I plumbed in an outdoor supply to our stove, but it doesn't seem to make a bit of difference whether it's open or closed. However, I have to admit that our house is hardly 'tight'. The HVAC guys put two 6" makeup ducts to the furnace room, so any negative pressure in the house is quickly relieved.Scott.Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.â€
Don't know about woodstoves but I found that supplying makeup air made a difference in fireplace performance, in fact a couple didn't work without it. Woodstoves, as the article states are a different issue and the impact of wind on house exteriors can be enormously variable.
Hi Scott,
My airtight firebox also receives combustion air from the outside. I can control the rate of burn quite effectively by adjusting the damper.
If your fire doesn't seem to be effected by adjusting your opening, it's possible the unit is not as airtight as mine.
Perhaps I wasn't clear when I said "doesn't make a bit of difference". The intake damper on the stove works very well to control combustion. The part that doesn't seem to make a difference is whether I use the outdoor air supply. I can pack it full of fiberglass and the stove continues to perform perfectly well.Scott.Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.â€
Interesting for sure. It seems to make sense. I also agree w/ dovetail ... it seems to lack documentation. It has a bit of ring of a pitch to sell wood stove heat and get over the hump of the buyer skeptics that have heard about the combustion air thing.
It seems to offer little in terms of a real solution ... open a window, I guess ... just make sure it is on the windward side (?). It also doesn't offer this discussion in contexts other than wood heat. Other combustion appliances aren't much different, really. A furnace, boiler, or water heater.
So ... if I install a direct connect high efficiency furnace w/ ducted combustion air ... I can potentially have a problem back drafting back through the intake? Maybe that doesn't matter (I have to think that it actually will matter very much, though).
The article mentions nothing about other conventional combustion appliance applications. Outside combustion air is often required for furnaces/water heaters. The article is basically saying that is bunk as well?
Many modern home have been constucted very meticulously to significantly reduce air leakage. This can impact combustion appliances in a significant way. I'm not talking about your average house construction that uses caulking and sealing in many of the most obvious places.
I have NEVER heard any argument about combustion appliances sucking the oxygen out of a house. My reaction is that is preposterous. Providing combustion air has always been focused on preventing backdrafting of the appliance and to contol the makeup combustion air for the appliance (to minimize 'uncontrolled air leakage').
While the article tends to make some solid sense, it also seems very incomplete. Not sure I get the mathematical equation, either. Not sure I could actually put any numbers in that one. I know it is to illustrate a concept, but it really doesn't do anything for the science that it is trying to support.
I hope some other people will jump in here and fill the gaps that I am obviously leaving. Maybe you could fill some gaps as well.
On the surface, this is kind of an embarrassing article by woodheat.org. Any intelligent person will get the sense that it lacks completeness, references, and a degree of logic.
To me it is much like someone trying to sell you something by talking about concepts or showing you a demonstration that is 'scientific', but that takes the science out of context to do so. On the surface, he's correct, but under closer scrutiny there is a degree of half truths to what he is saying ... so what he says is in fact true, but only w/in the narrow context of what he is saying.
Kind of like taking out a home equity loan to pay off your credit cards. Yes, in FACT, your monthly outlay will be lower ... but that is not necessarily a good thing.
We are missing a lot in this discussion and I hope that others will chime in with their two cents as well.
I didn't read the article, but I think that it needs to be pointed out that wood stoves and fireplaces are very different things. A fireplace will shoot air up the chimney (and thus out of the house) like water out of a fire hydrant. Wood stoves are generally designed to limit the amount of oxygen to burn the wood more efficiently. It's oxygen use is more like water dripping from a faucet (though it varies a great deal from model to model).
here's a link to a page on the same site that has references to the documentation:
http://www.woodheat.org/outdoorair/outdoorair.htmI've had this same discussion with my father-in-law. He's obsessed with outside air. I've never seen a clothes dryer need a separate outside air source, or a bath fan, etc. They draw more air than a wood stove. No?
In fairness, remember, those two examples use fans to force air out ... and do not rely on natural drafting of the appliance/combustion process to do so.
The RATE of combustion will determine the relative need/demand for combustion air and the other guys seem to have a point ... fireplaces are different than wood stoves ... at least TRADITIONAL style fireplaces ... which are a little uncommon in newer houses.
Hi Scott
I live up in Canada. Brick Wood burning fireplaces were the rage back in the 70's and 80's and were installed in a lot of homes, including mine. We have natural gas furnace heating and nat gas water heating. Every year up here, usually in the fall, some folks forget to leave a window open when using these fireplaces and what happens is the fireplace draft burns and sucks the air from inside the house until the exhaust gases from furnaces and water heaters reverse and start flu gasses coming back into the house.
If you want, you can google the City of Calgary website and search for woodstoves, you will find more info about this problem.
The airtight woodstove at my cabin does not burn any air from inside the house. It has a vent that runs out the wall behind it about the size of a dryer vent that brings in all the combustion air. The stove is rated as quite efficient and might be a little too big for the cabin because to reach optimum efficiency and prevent a buildup in the flu,I believe the fire in the firebox should be burning briskly. If we burn at a brisk rate, it gets too warm in the cabin. I've been told that damping the fire contributes to a creosote buildup in the flu.
We burn mostly pine,larch and some cedar and birch. The primary heat in the cabin is electricity. If we didn't use the the woodstove our electric bill would be very high. Some wood is still free around here if you are willing to go out each fall and get it. The local forestry people set aside some area's just for this purpose.
One interesting way to get outside air for a wood stone is to have a firewood box that is a drawer built into the outside wall near the stove. The drawer is on heavy duty full extension guides and can slide to the outside to the wall to be loaded with firewood, then when pushed closed on the outside, the firewood appears inside the house (no tromping in and out with armloads of firewood.The drawer is gasketed, but can be left ajar for any amount of fresh air needed for the stove or to cool an overheated room.
I very seldom use my upstairs masonry/brick fireplace because of my concern about pulling back flu gasses. The masonry/brick fireplace does have an outside opening that enters the fireplace from under the fire. This opening, which has an outside door and a metal flap on the floor of the fire chamber is for emptying ashes to the outside. I know a lot of air is drawn into the firebox through this opening because if I didn't empty the ashes out, the house would soon smell a bit of the ashes. I imagine a lot more air would be drawn through this opening during a fire.
My furnace and my hot water heater are both natural gas and use the principal of "hot air rises" to carry flu gasses up through the exhaust pipe to vent out the roof.
Every year up here, usually in the fall, some folks forget to leave a window open when using these fireplaces and what happens is the fireplace draft burns and sucks the air from inside the house until the exhaust gases from furnaces and water heaters reverse and start flu gasses coming back into the house.
Sledge, you hit the nail on the head. That article that Scott posted a link to is pure garbage, misleading and dangerous information.
Make up air is a MUST!!
I have never seen a house tight enough to cause a problem with what is being discussed here.
If houses were that tight we would all be dead and water would be dripping from the ceilings and walls.
With that said. I think makeup air units would make us all heathier. Our heating unit's would all peform better and life would (as Sarah P would say) dandy.
Russell
"Welcome to my world"
Believe me it happens. I was a skeptic as well until I took a class with an indoor eviromental specialist.
He put a news clipping on the screen for us all to read. He then went on to explain exactly how the co was sucked into the living area of the home from the burning embers in the firepace, caused by a central air return. (rather than individual room returns) With all the bedrooms shut off, the air returned looke for a place to get air and found it in the fireplace flue. Problem was that the fire was still glowing which also happens to be when it emits the most co.
A whole family never woke the next day.
It happens more than we think or want to believe.
I was not saying it is not possible.
I just have not seen a true tight house yet.
And I would'nt want mine that tight.
Russell
"Welcome to my world"
I do not believe it requires a very tight house to enable flu gases to be drawn back into the house. Shortly after I bought this house in 1974 I had a nice roaring fire going in the fireplace and the flu gases started back into the house. I was lucky that I detected it. I confirmed that this was happening by checking the hot water tank(nat gas heat)flu which was ice cold even though the flame was on reheating the tank. After framing the furnace and hot water tank area I made allowance for fresh outside air in that room.
Where i live it is now a requirement that furnaces have their own supply of combustion air. Friends who bought a new home 6 years ago have a separate flu from outside that ends directly in front of the nat gas furnace. This flu has a big red sticker warning not to block the flu which is a temptation because untill they closed off the furnace and hot water tank room, the whole basement was very cold in the winter. My friends do not have a wood burning fireplace.