Cat stoves don't nessecarily use less air. Only if they are being run low and slow. But if they are being run at equal burn rates they will use very similar amounts of air
Does Outside Air increase the Efficiency of woodstoves?
- Thread starter robllachance
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It seems to me, that is one of the factors (perhaps the most important one) not considered in this analysis. How is combustion affected by inlet air temperature?
I can’t be right all the time.🤣🤣
I like to leave OAK as a type of wood we burn. Don’t confuse me man.🤣
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that's your only problem, it took me months to figure out what IDK meant, IIRC and OAK too
nola mike
Minister of Fire
Your link isn't talking about an OAK from what I gather. It is talking about preheating the combustion air by using the chimney. So actually closer to using air from within your housing envelope than from an OAK.
nola mike
Minister of Fire
If not much, than OP's analysis is still valid. If there's a benefit to pre-heated air in terms of stove efficiency (@St. Coemgen 's link and others I've seen suggest there is), then an OAK is detrimental.
But he is talking about heating efficiency by his own words. And in that case there is definitely a benifit
nola mike
Minister of Fire
Rereading the original post, now I'm actually not sure which he's talking about. Stove efficiency should decrease if anything with an OAK. Heating efficiency I don't think is definite benefit. It really depends on the air turnover in your house at baseline, and if the stove is able to decrease the pressure in your house enough to increase air infiltration (in my 115 year old house, I'd be shocked if that were the case). The leakier your house, the less likely an OAK would be beneficial. Not sure where the tipping point is...
Yes combustion efficiency if anything would go down unless the cooler denser air helps. But either way that difference would be very minor. But even if you have enough air exchange to make an OAK un nessecary that doest change the fact that without one the stove is sucking heated air out of the house. So there is really no way that can possibly be beneficial to heating efficiency.
Doesn't the stove heat its incoming air, any way it gets it? Either inside air is heated before being sucked into the stove, or OAK air is heated inside the stove before combustion.
Yes bit one way the air has already been heated inside the house and is then sucked out to be replaced with air that needs to be heated again. With outside air it's just heated one time in the firebox and expelled out the chimney.
The whole discussion is silly if it's reasonably easy to run outside air there will almost always be some benefit even if it's only keeping humidity up in the house.
nola mike
Minister of Fire
My point is that the stove isn't necessarily sucking heated air out of the house. That air will be coming and going out of a leaky house regardless. The stove will give it a somewhat more preferential exit point, but (leaky house) won't have a significant impact on how much new cold air enters and needs to be heated. If the stove is more efficient heating with warm air, then heating efficiency would be better in that scenario
The more important question is:
What is the temperature differential between using room air versus air that is potentially zero or sub-zero (down to at least -36 here at times) and what effect, if any, does that have on the stove body itself, the internal stove temperatures, and/or room temperatures?
So explain how an OAK has an effect on keeping humidity in the house.
I’ll submit that I think there’s no effect either way. Even the old Seigler gas stoves in country stores had water pots on top of them back in the day, just as they placed water pots on wood stoves and coal stoves. Hot metal gives off dry heat, period.
I’ll submit that I think there’s no effect either way. Even the old Seigler gas stoves in country stores had water pots on top of them back in the day, just as they placed water pots on wood stoves and coal stoves. Hot metal gives off dry heat, period.
No excess dry outside winter air being pulled into the house is what reduces humidity in the house a stove using outside air won't reduce inside humidity
Essentially not at all. Air has a very small heat capacity so inlet temperature is not really a factor in this oxidation reaction.
I created an account on this forum just to post here that the OP is completely and totally wrong and to restate what others have said and maybe say it in a different way that will make sense to more people:
ANY appliance/device that creates negative pressure in a home by consuming or exhausting interior air is creating a vacuum in the home that is replaced with outside air. This is confusing to consumers as the depressurization is not accounted for in official efficiency specifications on products, a few examples that may illustrate the affect:
-a clothes dryer exhausts a lot of air from the home which is replaced with outside air
-bathroom fans and kitchen exhaust fans exhaust air which is replaced with outside air
-any appliance that burns any type of fuel that does not have a system for using outside air for combustion create a vacuum in the home which is replaced with outside air.
The reason the affects of these appliances arent part of the specifications on products is that the amount of heat/cooling needed to make up the exhausted air is dependent on several variables: the temperature of the outside air, the amount of air exhausted, how long you run the device, etc. There is no single number manufacturers/govt can put on a device to illustrate the affect however for most appliances you can calculate the heat loss with an anemometer, outside temps, and common equations. For all practical purposes it does not matter how drafty or airtight the house is. In an airtight house, these appliances will create negative pressure and as soon as you open the door to go outside the pressure will equalize and cold outside air will come in.
ANY appliance/device that creates negative pressure in a home by consuming or exhausting interior air is creating a vacuum in the home that is replaced with outside air. This is confusing to consumers as the depressurization is not accounted for in official efficiency specifications on products, a few examples that may illustrate the affect:
-a clothes dryer exhausts a lot of air from the home which is replaced with outside air
-bathroom fans and kitchen exhaust fans exhaust air which is replaced with outside air
-any appliance that burns any type of fuel that does not have a system for using outside air for combustion create a vacuum in the home which is replaced with outside air.
The reason the affects of these appliances arent part of the specifications on products is that the amount of heat/cooling needed to make up the exhausted air is dependent on several variables: the temperature of the outside air, the amount of air exhausted, how long you run the device, etc. There is no single number manufacturers/govt can put on a device to illustrate the affect however for most appliances you can calculate the heat loss with an anemometer, outside temps, and common equations. For all practical purposes it does not matter how drafty or airtight the house is. In an airtight house, these appliances will create negative pressure and as soon as you open the door to go outside the pressure will equalize and cold outside air will come in.
AFAIK, the stove needs combustion air from someplace. If it gets it from the outside via an OAK, the air will usually be colder. If the combustion air comes from the indoor space around the stove, it will usually be warmer. Colder air will use some firebox heat to warm up to match the temperature of the surrounding room, but the effect is small. Colder air will also be more dense and thus will contain more oxygen, but again the effect is small. The efficiency of the stove in isolation is close to the same either way.
If air is brought in via an OAK and the pipe from the stove to the outside is very short, the room air temp will be essentially unaffected by the cold pipe. If the pipe is long, there may be a small effect cooling the room and warming the combustion air.
If the combustion air is brought in via an OAK, the stove will not reduce the pressure in the conditioned space. The stove will be (almost) a pure heat source. If the combustion air is obtained from the room, it will reduce the pressure in the room, pulling air in from outside in hard-to-predict ways. That will increase ventilation into the conditioned space, and reduce temperatures somewhat near the points of air entry. The heat needed to warm that air is essentially the same as the heat that would be needed to warm OAK air in the firebox, so the overall efficiency is still about the same. But the pressure change is likely to cause air to flow from parts of the conditioned space further from the stove towards the stove, cooling the more remote areas somewhat.
Exhaust fans (e.g., bathroom fans) do not produce significant heat, and thus have an almost pure cooling effect.
Clothes dryers create heat but generally exhaust most of it.
My NG furnace uses room combustion air and has the usual exhaust vent for combustion products. It has another vent roughly resembling an OAK, but that vent feeds into the air distributed into the conditioned space, not into the combustion chamber, and there is a timer that keeps that vent closed most of the time. The furnace is still capable of heating the entire indoor space fairly evenly. It might be slightly more efficient if it used outside combustion air, but code requires bringing fresh air into the indoor space to improve air quality.
If air is brought in via an OAK and the pipe from the stove to the outside is very short, the room air temp will be essentially unaffected by the cold pipe. If the pipe is long, there may be a small effect cooling the room and warming the combustion air.
If the combustion air is brought in via an OAK, the stove will not reduce the pressure in the conditioned space. The stove will be (almost) a pure heat source. If the combustion air is obtained from the room, it will reduce the pressure in the room, pulling air in from outside in hard-to-predict ways. That will increase ventilation into the conditioned space, and reduce temperatures somewhat near the points of air entry. The heat needed to warm that air is essentially the same as the heat that would be needed to warm OAK air in the firebox, so the overall efficiency is still about the same. But the pressure change is likely to cause air to flow from parts of the conditioned space further from the stove towards the stove, cooling the more remote areas somewhat.
Exhaust fans (e.g., bathroom fans) do not produce significant heat, and thus have an almost pure cooling effect.
Clothes dryers create heat but generally exhaust most of it.
My NG furnace uses room combustion air and has the usual exhaust vent for combustion products. It has another vent roughly resembling an OAK, but that vent feeds into the air distributed into the conditioned space, not into the combustion chamber, and there is a timer that keeps that vent closed most of the time. The furnace is still capable of heating the entire indoor space fairly evenly. It might be slightly more efficient if it used outside combustion air, but code requires bringing fresh air into the indoor space to improve air quality.
Great discussion, thank you all for the contributions and keeping it civil. This topic has been a hot one for decades. Efficiency is not the only reason for an OAK. In a tight house it may be necessary to support combustion or to reduce competition with other combustion appliances. Tom Oyen did this write up years ago, but it made good points. The comments and responses are interesting too.
Sweep's Library - Why burn outside air?
Should I burn outside combustion air in my stove or fireplace?
hearth.com
One more thing to consider: if combustion products from the stove reach the top of the chimney and keep going up, or are blown by the wind and diluted, they are unlikely to be pulled back in to the house. (Your house, anyway.) Otherwise, the combustion products may be present in the air outside the house.
If combustion air is brought in via an OAK, it will be acquired at one point and will go directly to the firebox, most likely with very little air leakage. Any combustion products around the house will not be pulled into the conditioned space. If the air is supplied by the room, the source of the replacement air will likely be diffuse. The outdoor combustion products are more likely to be pulled into the conditioned space.
My local geography means that some of the combustion products often remain near the house. I installed an OAK partly to avoid having them pulled back into the house, and partly to simplify distributing the stove's heat to the most distant parts of the conditioned space.
If combustion air is brought in via an OAK, it will be acquired at one point and will go directly to the firebox, most likely with very little air leakage. Any combustion products around the house will not be pulled into the conditioned space. If the air is supplied by the room, the source of the replacement air will likely be diffuse. The outdoor combustion products are more likely to be pulled into the conditioned space.
My local geography means that some of the combustion products often remain near the house. I installed an OAK partly to avoid having them pulled back into the house, and partly to simplify distributing the stove's heat to the most distant parts of the conditioned space.
Ashful
Minister of Fire
I guess "more likely" is a fair way to put it. Your house is pulling in outside air all the time, with or without a stove, due to chimney effect as well as other appliances (clothes dryer, furnace, water heater, range hood, bathroom exhausts, radon system, etc.). The stove only adds to that.
i just read this whole thread and i still have no idea what to do. i just bought an old 1000sqft house in upstate NY and plan to put a wood stove in and hope to use that more than the oil forced air system in there now.
my initial thought was an outside air supply seemed obvious, why would you suck the warm air out of you house when you can get outside air for free. but now i'm not sure.
surely someone on here as done a side by side test of using and then disconnecting an OAK inlet to see what the difference in comfort and fuel use is?
this guy did a test and got his cabin warmer quicker from an OAK
my initial thought was an outside air supply seemed obvious, why would you suck the warm air out of you house when you can get outside air for free. but now i'm not sure.
surely someone on here as done a side by side test of using and then disconnecting an OAK inlet to see what the difference in comfort and fuel use is?
this guy did a test and got his cabin warmer quicker from an OAK
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