Are most people using outside air for combustion in their wood stoves in air tight homes? If so, do you feel there is a benefit to it?
Using outside air for combustion
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I am beginning the process of looking for a new stove and one feature I am definitely going to look for is an outside air kit. From what I have heard and read, they help with well insulated houses.
I had planned an OAK installation, just assumed it would be required. The installer advised me to wait and see if it was needed, said that he had seen them turn into ice-dam nightmares in this climate (a little bit to your northwest). Said he'd install one if I wanted, but if it were him, he'd wait. I was surprised, but thought that made sense, and said yes, and I"m glad I did.
I've had a problem in prior years with too much moisture in this house, because it is excessively tight. I had a blower-door test done, and my house tested so tight that an HRV system was recommended. I researched them, and decided to wait and see what a woodstove would do to improve air turnover. My woodstove has been sufficient to virtually eliminate the ice-on-the-windows problem. My house is getting more air turnover, thanks to the healthy draft, and I've seen no sign of the typical symptoms of not-enough-fresh-air-in-here, such as headaches, lethargy, etc.
My house is built into a sidehill, and the upstairs back door is at the landing of the stairs. The bottom of the stairs opens into the dining room (which is also my hearthroom), and there is a big open headspace above the stairs, so warm air has a reservior in which to accumulate before mixing with the upstairs air. That reservoir is also high enough that the heat can go higher than the door and make the rounds, rather than being funneled to the back door to escape. Some of it mixes with the cold air that is pulled in from around that door to result in cool--not chill--air flowing across the dining room/hearthroom to the stove; thus, no sensation of discomfort from the air exchange, but a discernable sense of air movement flowing at ankle height sometimes times around the foot of the stairs, like wading in a slow-moving stream. Because that air movement takes place in such a limited line from the door, down the stairs, across the floor to the stove, there is no associated discomfort, but plenty of fresh air inside.
Essentially, I have an OAK-by-serendipity--I lucked out. However, I'd never have known that if I'd gone with the assumption that I needed an OAK, or had an installer who thought I needed one, or who would have advised me to install one to pad the job. Likewise, if I'd installed the HRV, I'd not have had a chance to see what the stove could do without it. My house is plumbed for an HRV system, and I'm thinking about putting some duct fans in to move warm air from the ceiling of the dining room up to the bedrooms on cool nights (again, just got lucky that they're laid out thus).
Getting to know how your house is going to respond to a heating system is a sometimes-fun, sometimes-frustrating, really-interesting process of exploration, and I encourage you to take your time to learn how it will respond, and "above all, do no harm". If I take into account what this may have saved me on an HRV, this stove is looking like a better deal all the time. That's my experience and thoughts, fwiw. Good luck finding the right answer for you.
I've had a problem in prior years with too much moisture in this house, because it is excessively tight. I had a blower-door test done, and my house tested so tight that an HRV system was recommended. I researched them, and decided to wait and see what a woodstove would do to improve air turnover. My woodstove has been sufficient to virtually eliminate the ice-on-the-windows problem. My house is getting more air turnover, thanks to the healthy draft, and I've seen no sign of the typical symptoms of not-enough-fresh-air-in-here, such as headaches, lethargy, etc.
My house is built into a sidehill, and the upstairs back door is at the landing of the stairs. The bottom of the stairs opens into the dining room (which is also my hearthroom), and there is a big open headspace above the stairs, so warm air has a reservior in which to accumulate before mixing with the upstairs air. That reservoir is also high enough that the heat can go higher than the door and make the rounds, rather than being funneled to the back door to escape. Some of it mixes with the cold air that is pulled in from around that door to result in cool--not chill--air flowing across the dining room/hearthroom to the stove; thus, no sensation of discomfort from the air exchange, but a discernable sense of air movement flowing at ankle height sometimes times around the foot of the stairs, like wading in a slow-moving stream. Because that air movement takes place in such a limited line from the door, down the stairs, across the floor to the stove, there is no associated discomfort, but plenty of fresh air inside.
Essentially, I have an OAK-by-serendipity--I lucked out. However, I'd never have known that if I'd gone with the assumption that I needed an OAK, or had an installer who thought I needed one, or who would have advised me to install one to pad the job. Likewise, if I'd installed the HRV, I'd not have had a chance to see what the stove could do without it. My house is plumbed for an HRV system, and I'm thinking about putting some duct fans in to move warm air from the ceiling of the dining room up to the bedrooms on cool nights (again, just got lucky that they're laid out thus).
Getting to know how your house is going to respond to a heating system is a sometimes-fun, sometimes-frustrating, really-interesting process of exploration, and I encourage you to take your time to learn how it will respond, and "above all, do no harm". If I take into account what this may have saved me on an HRV, this stove is looking like a better deal all the time. That's my experience and thoughts, fwiw. Good luck finding the right answer for you.
I provide outside air to my wood stove, water heater, dryer, and fireplace. The kitchen and baths are provided outside air from the basement supply. Combustion air has to come in. I choose where.
I used insulated flex duct. It was cheap when we built. Flex was easy for me to install and it prevents condensation. I don't use heat exchangers on the exhaust/outside air, since we live in the south part of Missouri. Probably could save some Btus but would not pay off financially. Colder climate, perhaps.
When the dryer is running and the wife kicks in the downdraft cook top, I know my wood stove and fireplace will not feel the drop. And, there will not be a flow of cold outside air across my precious little feet.
I used insulated flex duct. It was cheap when we built. Flex was easy for me to install and it prevents condensation. I don't use heat exchangers on the exhaust/outside air, since we live in the south part of Missouri. Probably could save some Btus but would not pay off financially. Colder climate, perhaps.
When the dryer is running and the wife kicks in the downdraft cook top, I know my wood stove and fireplace will not feel the drop. And, there will not be a flow of cold outside air across my precious little feet.
JimboM said:
Having outside air supplied to a dryer is a brilliant idea--never occured to me, but I do begrudge my dryer those btu's. However, I don't think outside air supplied to the bathroom would go over very well here in the fridgid northland.
If I may jaywalk here, how does insulated flex duct prevent condensation?
snowleopard said:
My thinking was any surface inside the house that is cooler than the dew point of the interior air would have condensation. An uninsulated pipe flowing cold air would qualify. The insulation and vapor barrier on the flex eliminates the cold surface in contact with warm moist air. We see condensation at times on windows close to the showers. We also have the dog breath condensation and slobber on the window problem.
We planned to install one, but after reading the following article on woodheat.org decided against it.
http://woodheat.org/index.php?option=com_content&view=article&id=81&Itemid=15
We do have an ERV.
http://woodheat.org/index.php?option=com_content&view=article&id=81&Itemid=15
We do have an ERV.
Some interesting points in this article, but it is more hypothetical than scientific.WhitePine said:
1. One reason for outside air--no matter how tightly your home is constructed--is so that inside air that you've spent money to heat does not get sent up the flue to outside. Presumably your wood/money goes farther if you don't have to keep heating a constant stream of outside air that leaks into your home to replenish what you're taking from inside.
2. Another reason for using outside air is a new home that has a well-installed continuous air barrier (think Tyvek or similar) with properly installed doors and windows etc. and has very little air leaking to the interior. That situation means when you take combustion air from inside, there's no natural air leakage to replenish it. A flue might not draw well in those circumstances, just like it's difficult to suck air from a straw with one end closed. However, a new home does not guarantee an airtight home....only a blower door test can really confirm how air-tight your home is.
3. Another reason might be that you have appliances competing for air or an unusual condition such as a basement stove. Dryers, bathroom fans, kitchen fans, boilers that are not closed combustion systems, etc. will all be taking air from inside your home and sending it outside. This might affect your flue's draft, especially if you have a tight house, since all the air leaving depressurizes the interior.
4. Yet another reason for outside air is better control of interior comfort. Outside winter air is generally dry. The more interior air you send outside, the more dry winter air leaks in, and the humidity inside your home decreases. Of course, this one is a bit complex, since humidity levels also depend on the activities in your home, how air-tight the home is, and use of other control means such exhaust fans.
2. Another reason for using outside air is a new home that has a well-installed continuous air barrier (think Tyvek or similar) with properly installed doors and windows etc. and has very little air leaking to the interior. That situation means when you take combustion air from inside, there's no natural air leakage to replenish it. A flue might not draw well in those circumstances, just like it's difficult to suck air from a straw with one end closed. However, a new home does not guarantee an airtight home....only a blower door test can really confirm how air-tight your home is.
3. Another reason might be that you have appliances competing for air or an unusual condition such as a basement stove. Dryers, bathroom fans, kitchen fans, boilers that are not closed combustion systems, etc. will all be taking air from inside your home and sending it outside. This might affect your flue's draft, especially if you have a tight house, since all the air leaving depressurizes the interior.
4. Yet another reason for outside air is better control of interior comfort. Outside winter air is generally dry. The more interior air you send outside, the more dry winter air leaks in, and the humidity inside your home decreases. Of course, this one is a bit complex, since humidity levels also depend on the activities in your home, how air-tight the home is, and use of other control means such exhaust fans.
triathlete said:
Possibly, but I have a fairly high regard for Canadian regulators, as opposed to those in the US. Besides, not having an outside air kit has not presented us with any issues. It also allowed us to install a stove model with legs, which we find more attractive than the pedestal models. That's strictly a personal preference, but we really couldn't have done it with an OAK, at least not without a clunky appearance.
elmoleaf said:
The duct work bringing the outside air to the stove has to be air tight and very well insulated, or you will lose heat that way too.
elmoleaf said:
A tight house should have an ERV or HRV or indoor air quality (IAQ) will be bad from out gassing of the construction materials, etc. They are required in some jurisdictions. Despite not being designed for makeup air, an ERV or HRV can supply enough fresh air that the stove will not depressurize the house to any significant degree. Wood stoves simply don't use that much air.
triathlete, For the last 43 years my winters have been spent in Alaska, Idaho and New York. During winter months I suffered through chronic asthma and bronchitis each of those years. My Alaskan home had a fireplace w/o an OAK. My home in Idaho had a wood stove w/o an OAK. This is my sixth year living in a new home I built in New York. The house is a three bedroom, single story ranch with a full walk-out basement. During the first four of these six years I had no wood stove and suffered my usual asthma and bronchitis.
My new house is heavily insulated and sealed so two years ago when I installed the new PE Spectrum I also installed the OAK. There is a double hung window close behind the wood stove. I almost always have the upper half of that window open about 3/8" to allow the introduction of a little fresh air. Because the window opening is so close to the stove any cold air entering the house is quickly warmed by the closeness of the wood stove. There are no cool drafts in my house.
Last year and this year are the only two of the last 43 years when I have not had any spells of asthma or bronchitis. Are the wood stove, OAK and slightly open window instrumental in eliminating my respiratory distress? I cannot say for certain. However, these are the only changes to my winter life style so I have to believe they helped just a little, anyway.
Best wishes and good luck whatever you decide to do.
My new house is heavily insulated and sealed so two years ago when I installed the new PE Spectrum I also installed the OAK. There is a double hung window close behind the wood stove. I almost always have the upper half of that window open about 3/8" to allow the introduction of a little fresh air. Because the window opening is so close to the stove any cold air entering the house is quickly warmed by the closeness of the wood stove. There are no cool drafts in my house.
Last year and this year are the only two of the last 43 years when I have not had any spells of asthma or bronchitis. Are the wood stove, OAK and slightly open window instrumental in eliminating my respiratory distress? I cannot say for certain. However, these are the only changes to my winter life style so I have to believe they helped just a little, anyway.
Best wishes and good luck whatever you decide to do.
triathlete, as a counter to the excellent argument presented in woodheat.org, I would suggest you also read this excellent argument: http://www.chimneysweeponline.com/hooa.htm
To me, the argument at chimneysweep is the more intuitive and convincing of the two.
To me, the argument at chimneysweep is the more intuitive and convincing of the two.
Leaky house or not. I think its the climate conditions for sure is what dictates it. For me it was the better control of humidity and cold drafts where I don't want them. Also no more ice build up at doors and windows.
Thanks for this article. I agree ... it seems more convincing to me too.John_M said:triathlete, as a counter to the excellent argument presented in woodheat.org, I would suggest you also read this excellent argument: http://www.chimneysweeponline.com/hooa.htm
To me, the argument at chimneysweep is the more intuitive and convincing of the two.
From personal experience, I lived in an air-tight home and wondered why I had so many headaches and was tired so often during the winter. It could have been a number of things, but I suspect now that it was an environment of low oxygen created by burning the woodstove 24/7 without an OAK. I'm planning to build a new house, and to be on the safe side I will certainly install an OAK based on the advice I've read here. I really appreciate the help and perspective on both sides of this matter. Thanks to all.
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