Outside Air Kits, Do you recommend them?

[tradergordo]

The Burnahm outside air kit has a backflow preventer damper which would close in the event it gets clogged or there is negative pressure, causing the burner to draw air from the room.

Page 36 of this document has a diagram:
http://www.burnham.com/pdfs/CurrentPDFfiles/8142824.pdf

Looks like a good design - but now you need even MORE draft to overcome this mechanism (intake air now has to force open a louver). This probably works well in an oil fired furnace/boiler because they use more intake air than a wood stove. I'm not sure how well it would work with a woodstove, but I suppose in the worst case you would just be drawing air from the room all the time which would be about equivalent to not having the outside air kit at all. Then again, perhaps the forces from negative pressure events could still weaken your draft even though air flow isn't running backward.

 

[tradergordo]

Im a fan of the passive kits, like the condar asv-90. Good link tradergordo, thats exactly what was happening to my customers, The outside air was on the east side of the house with a marginal chimney. Wind blows here usually from west to east. The installed it against my recomendation and then had the guts to call me and tell me my stove i sold them was broken (Jotul Oslo). There exact words "this stove shouldnt send smoke and sparkes out the side of my house, i want my money back". Thats exactly what they got, i didnt argue a bit, i explained the problem was the outside air kit, they didnt believe a word i said. I picked it up the next day to avoide getting into a lawsuit when there house burnt down.

Hah! You should send them a copy of that report. They probably bought another stove from someone else and had the same problem. What a shame. Yes, these outside air kits could be dangerous.

p.s. The passive kits don't work either!


Passive make-up air supplies
A passive make-up type air supply is one that is not connected directly to the fireplace or stove combustion chamber. Since it is connected only to the house environment and not to the appliance, it flows air into a house only when the pressure inside is lower than the pressure outdoors, since air only flows to zones of lower pressure. Passive air supplies don't make wood burners work better, they just make the house leakier.


Passive air inlets are nothing more than holes in the wall. Wind effects may force air into the house or suck it out of the house, depending on the location of the hole relative to wind direction.


Wind effects around the house also affect the direction and volume of flow through a passive inlet. If the weatherhood of a passive inlet is on the windward side of a building, wind pressure is likely to force air into the building; if the weatherhood is on the downwind side, the negative pressure zone created by the wind is likely to draw air out of the house, possibly depressurizing it.
More importantly, it is misleading to think of the hole in the wall approach as supplying combustion air. In fact, passive air supplies provide air only in response to pressure differences. In cold weather, when temperature difference produces a pressure difference due to stack effect, if a passive make-up air supply is located below the neutral pressure plane of the house (and there is no wind effect and no exhaust systems are operating), air will flow into the house. If, on the other hand, the passive inlet is located above the house neutral pressure plane, air will flow out.

Passive air inlets do not supply combustion air, but flow air only in response to pressure differences. Here, the flow direction depends on where in the house the passive hole is located.


It is useful to keep in mind a key physical principle:
AIR FLOWS TO ZONES OF LOWER PRESSURE through any available opening.

The real problem with the passive make-up air strategy is that it does not reliably supply combustion air, nor does it reliably reduce combustion spillage. Under favorable conditions it may tip the balance of driving and adverse pressures in favor of successful venting. This is why some fireplace specialists have reported performance improvements after the installation of a passive supply. However, it is also possible for a passive supply to cause spillage if air is drawn out of the house into a low pressure zone caused by wind effects. A remedial strategy that only works sometimes, and that may make the problem worse, is not a good strategy. A passive make-up air supply is really nothing more than another uncontrolled leak in the house envelope. A leaky house envelope is no guarantee of successful venting.

 

[velvetfoot]

I think it could work. Then again, we couldn't even tell HOW the outside air was routed to the old zero clearance fireplace, just that there was a short duct to somewhere in there. It'd be nice to have a more engineered layout, similar to the oil burner example above, which who knows, might still be controversial in certain circles . As I said, the area around my fireplace got quite cold from the outside air.

 

[Todd]

Im a fan of the passive kits, like the condar asv-90. Good link tradergordo, thats exactly what was happening to my customers, The outside air was on the east side of the house with a marginal chimney. Wind blows here usually from west to east. The installed it against my recomendation and then had the guts to call me and tell me my stove i sold them was broken (Jotul Oslo). There exact words "this stove shouldnt send smoke and sparkes out the side of my house, i want my money back". Thats exactly what they got, i didnt argue a bit, i explained the problem was the outside air kit, they didnt believe a word i said. I picked it up the next day to avoide getting into a lawsuit when there house burnt down.

Hah! You should send them a copy of that report. They probably bought another stove from someone else and had the same problem. What a shame. Yes, these outside air kits are dangerous.

p.s. The passive kits don't work either!


Passive make-up air supplies
A passive make-up type air supply is one that is not connected directly to the fireplace or stove combustion chamber. Since it is connected only to the house environment and not to the appliance, it flows air into a house only when the pressure inside is lower than the pressure outdoors, since air only flows to zones of lower pressure. Passive air supplies don't make wood burners work better, they just make the house leakier.


Passive air inlets are nothing more than holes in the wall. Wind effects may force air into the house or suck it out of the house, depending on the location of the hole relative to wind direction.


Wind effects around the house also affect the direction and volume of flow through a passive inlet. If the weatherhood of a passive inlet is on the windward side of a building, wind pressure is likely to force air into the building; if the weatherhood is on the downwind side, the negative pressure zone created by the wind is likely to draw air out of the house, possibly depressurizing it.
More importantly, it is misleading to think of the hole in the wall approach as supplying combustion air. In fact, passive air supplies provide air only in response to pressure differences. In cold weather, when temperature difference produces a pressure difference due to stack effect, if a passive make-up air supply is located below the neutral pressure plane of the house (and there is no wind effect and no exhaust systems are operating), air will flow into the house. If, on the other hand, the passive inlet is located above the house neutral pressure plane, air will flow out.

Passive air inlets do not supply combustion air, but flow air only in response to pressure differences. Here, the flow direction depends on where in the house the passive hole is located.


It is useful to keep in mind a key physical principle:
AIR FLOWS TO ZONES OF LOWER PRESSURE through any available opening.

The real problem with the passive make-up air strategy is that it does not reliably supply combustion air, nor does it reliably reduce combustion spillage. Under favorable conditions it may tip the balance of driving and adverse pressures in favor of successful venting. This is why some fireplace specialists have reported performance improvements after the installation of a passive supply. However, it is also possible for a passive supply to cause spillage if air is drawn out of the house into a low pressure zone caused by wind effects. A remedial strategy that only works sometimes, and that may make the problem worse, is not a good strategy. A passive make-up air supply is really nothing more than another uncontrolled leak in the house envelope. A leaky house envelope is no guarantee of successful venting.

My Condar ASV-90 seems to work for me. I have checked it out during windy days and it doesn't suck the air out of the house. My old stove use to smoke when I opened the door when the clothes dryer was running, after installing the make up air it didn't smoke any more. It does equal the pressure in the house, and I sapose it leaks cold air in too, but it's not enough to freeze me out of my house. I can leave the air ventilator wide open on a below zero day, and the stove still keeps the house at 80 degrees. Tight houses need something to equalize pressures and get some fresh air inside if not for combustion for health reasons also.

 

[MountainStoveGuy]

In the case of a customer that insists on outside air, sometimes a passive system is meeting in the middle. I agree, i dont think they work any better, but one thing for shure, they wont burn down the house.

 

[elkimmeg]

tradergordo: All research only test or mentions the one outlet location. Go back and read my response concerning multiple locations.
Have you found any research the proves my theory wrong and what if one puts a damper vlave to flow in the direction of highest pressure so it is not a constant opening at all times. Code requires damper bafflets in bath exhaust fans? same can be applied here but multi outlets or inlets This way one side actas for incoming pressues and one acts for out going pressure

 

[KP Matt]

This from a guy who claims:

Regular wood stoves and fireplaces use room air for combustion and suck outside air in through every crack, which makes them virtually useless in subzero weather because they bring in cold air faster than they can heat the room.

Open fireplaces, generally true. Regular wood stoves, on the other hand, are certainly not virtually useless in subzero weather, regardless of how poorly insulated your house might be and whether you have an outside air kit. I don't think there's any money to follow over at woodheat.org as concerns their rejection of the value of outside air kits. Are they making money removing people's old outside air kits?

 

[KP Matt]

If a system was to malfunction in Washington state, sending smoke and sparks out the side of the house as described by MSG, most of the sparks would land in puddles and soggy moss. A banana slug might get singed.

I was a little too critical of the Ripples character; his blog has some interesting things on it. But I think he is a little naive in his acceptance of the outside air kit, if in fact it is not required by code in his location.

If I might ask, how much does an outside air kit cost? Installed?

 

[MountainStoveGuy]

So maybe this thread needs to point towards more hands on data, there are two schools of thought, both on oppisit ends of the spectrum. I have stated my real life experence dealing with ouside air kits. I stated in the first post that there needs to be a "perfect storm" for this to happen, a very high percentage of installs would be fine. I think its important to identify your install and see if its a canadate for outside air. To totally dismiss the danger aspect is ignorant, to say that outside air kits will always work is ignorant as well. There is a danger, i have seen it. But i have also seen plenty that work. So from a dealer standpoint, do i default to the no outside air kits theroy and protect my butt, or do i leave it to the average consumers hands to make there own decision? When we are talking fire burning appliances in peoples homes i tend to air on the side of caution.

 

[Roospike]

So maybe this thread needs to point towards more hands on data, there are two schools of thought, both on oppisit ends of the spectrum. I have stated my real life experence dealing with ouside air kits. I stated in the first post that there needs to be a "perfect storm" for this to happen, a very high percentage of installs would be fine. I think its important to identify your install and see if its a canadate for outside air. To totally dismiss the danger aspect is ignorant, to say that outside air kits will always work is ignorant as well. There is a danger, i have seen it. But i have also seen plenty that work. So from a dealer standpoint, do i default to the no outside air kits theroy and protect my butt, or do i leave it to the average consumers hands to make there own decision? When we are talking fire burning appliances in peoples homes i tend to air on the side of caution.

You would have one hell of a time selling cars , thats for sure...........HA ! Well MSG has a story about the out side air kit. There are other posters here with actual out side air kits that say they have had no probelms . Anybody at all that has an actual out side air kit that has had a problem ? The issue was bashed over last year on here and dont ever recall ANYBODY that had an issue that actually had the out side air unit. Lots os storys tho . You would think if the out side air kits was such an issue #1 wood stove co wound not have them on ther stoves #2 The kits couldnt be sold #3 they wouldnt be CODE for moble homes & #4 They wouldnt be CODE for some states. I also searched the net for storys of issues with these outside ait kits and didnt find any news storys nor could i find a court case about them . Just a bunch a bla , bla , bla . We have heard posters here DO that have outside air kits with no problem ...........Any body have one that DOES have a problem ? Anybody ?

 

[tradergordo]

Another informative study would be for everyone with an outside air kit to go inspect the insides and around the intake vent and look for some signs of soot (evidence of it running backwards). Oh, and the danger from the thing running backwards isn't really because of sparks that might fly out and ignight something outside the house (although that is certainly a concern) - the danger I was thinking of was directly igniting the house. Most outside air kits use super thin single wall piping to the outside. Think about it this way - would you use the same material as a chimney going from your stove to your roof for example? Perhaps it would take extreme conditions to actually set a house on fire this way, perhaps it has never happened (yet) but than again how long have these been in use? It might take a decade or longer before any houses burn down.

The one way valves seem like a good idea for safety although I don't know if the airflow is then restricted? Notice that the passive kit mentioned here (condar) has an optional part you can purchase separately to restrict airflow to a single direction.

Elk - as for installing "x" number of holes in your house instead of just one... I don't know if that would really solve the problem? It may help though. Then again, if you are trying to avoid cold drafts which seems to be a big selling point for outside air kits, adding extra holes to different sides of your house probably isn't going to work for you.

I see both sides of the debate - like I said originally, I was at first dead set on buying an outside air kit... but now I think its probably not going to have any benefit to me and in the worst case senario could be dangerous. One thing I would like to do is actually get or borrow an air pressure meter and actually test my house to see if negative pressure is generated from the wood stove, and if so, how much? I would also test while the gas clothes dryer was running, and maybe turn on all the vent fans (kitchen and bathrooms) just to see how much negative pressure I can even generate in my house. Has anyone here done such a test?

I think the bottom line on this issue is that more research still needs to be done.

 

[Roospike]

Another informative study would be for everyone with an outside air kit to go inspect the insides and around the intake vent and look for some signs of soot (evidence of it running backwards). Oh, and the danger from the thing running backwards isn't really because of sparks that might fly out and ignight something outside the house (although that is certainly a concern) - the danger I was thinking of was directly igniting the house. Most outside air kits use super thin single wall piping to the outside. Think about it this way - would you use the same material as a chimney going from your stove to your roof for example? Perhaps it would take extreme conditions to actually set a house on fire this way, perhaps it has never happened (yet) but than again how long have these been in use? It might take a decade or longer before any houses burn down.

The one way valves seem like a good idea for safety although I don't know if the airflow is then restricted? Notice that the passive kit mentioned here (condar) has an optional part you can purchase separately to restrict airflow to a single direction.

Elk - as for installing "x" number of holes in your house instead of just one... I don't know if that would really solve the problem? It may help though. Then again, if you are trying to avoid cold drafts which seems to be a big selling point for outside air kits, adding extra holes to different sides of your house probably isn't going to work for you.

I see both sides of the debate - like I said originally, I was at first dead set on buying an outside air kit... but now I think its probably not going to have any benefit to me and in the worst case senario could be dangerous. One thing I would like to do is actually get or borrow an air pressure meter and actually test my house to see if negative pressure is generated from the wood stove, and if so, how much? I would also test while the gas clothes dryer was running, and maybe turn on all the vent fans (kitchen and bathrooms) just to see how much negative pressure I can even generate in my house. Has anyone here done such a test?

I think the bottom line on this issue is that more research still needs to be done.

Please dont take this question(s) the wrong way. #1 Do you know how the out side air kit would be installed on your stove ? What brand stove ? Unsure about other make and models , I can only speek for the Pacific Energy Summit stove. The outside air kit IS hooked up to the stove BUT, its not a direct air hook up. On the PE stove the outside air is hooked up to the back of the ash pan . The ash pan is where the air supply comes from to the stove , Its not an air tight system . I myself could not see how outside air kit could pull the air supply from the stove to change the draft . As stated , its hooked to the stove but not direct to the air supply.

 

[Roospike]

Copied a page of the PE Summit owners install guide. Shown in the picture where the air inlet supply can be installed . I would think if the air was pulled from outside (with outside air kit ) from a draft it would be more common to pull inside house air then to pull air from the fire or the chimney.

 

[thechimneysweep]

As the author of the website articles at (broken link removed to http://www.chimneysweeponline.com/hooa.htm) and (broken link removed to http://www.chimneysweeponline.com/hooa3.htm) , I thought I'd chime in here. I visit the forum infrequently and just stumbled across this thread today, and have comments about several statements that have been made above. In no particular order, here they are:

First, the one I'm a little steamed about. Ours is a retail website, but that doesn't affect the facts or opinions we present in our Sweep's Library. Most of those articles began as handouts we gave out to our chimney cleaning customers over 20 years ago, before we even had a retail store or internet website. These articles have been refined, expanded upon and corrected when necessary in the ensuing years, and we stand behind them. The insinuation made above that we promote outside combustion air because we profit from it is both unkind and untrue: aside from the fact that we happen to have more integrity than that, the parts we use to install an outside air intake to a Pacific Energy stove, for example, sell at any hardware store for about $15.00.

There is no need to wait for a decade of experience to determine the safety of direct outside air connection. Direct OA connection to the firebox has been a legal requirement for all modular and manufactured homes throughout the US for over two decades, and there has never been a report of a hazardous situation of any kind that resulted from the outside air hookup (even in the unique super-wind-pressurization scenario described in another post above). Further, ALL woodstove and fireplace installations in Washington State have required direct OA hookups for over a decade, with still not a single safety problem reported. We're talking tens of thousands of installations, and not a single documented case of damage of any kind caused by an outside air system.

Hot air does burn more efficiently in a woodstove than cold air. But the air introduced into the firebox by an outside air kit isn't necessarily cold: every woodstove we've ever seen that burns outside air has preheat chambers built into the sidewalls of the hot firebox through which the air must travel before it hits the fire. We have witnessed hundreds of cases where outside air improved the burn, but never a single case where it impeded it, regardless of the outside temperature.

By the way, these preheat chambers, along with baffling in the intake area and the industry-standard "airwash" design that introduces the combustion air into the firebox through a slot at the top of the viewing window, ensure that no burning material with enough density to cause a fire could possibly be forced from the floor of the firebox, up the inside of the glass, through the airwash slot, downward through the preheat chambers, around the baffling, through the intake pipe and all the way to the outside of the house in any conceivable atmospheric condition. MountainStoveGuy's statement that he has had customers report smoke and sparks "flying out of the side of their house" through their outside air intakes makes those customers the only reported witnesses to this phenomenon in history. And if he relates this tale to Jotul's engineers, he is in for a lengthy explanation of why this would not be possible with today's stove designs.

There are many advantages to burning outside combustion air in a woodstove or fireplace. It helps prevent exhaust intrusion into the room from the stove or fireplace (or other appliances in the home) due to room depressurization. It helps prevent cross-drafting. It ensures that the fire always has access to sufficient air for efficient combustion. It prevents drafts in the room caused by cold outside air being drawn in due to house depressurization. And these statements are not hearsay: I have personally witnessed the effectiveness of outside combustion air in hundreds of installations.

 

[MountainStoveGuy]

Why dont you explain why its impossible for smoke and sparks to come out of a modern stove? Im not here to prove anything to you, im hear to open up debate, you obviously think your findings are the gospel on this matter, but you can find otherweb sites that offer the oppisit views. This thread was not started to get links to websites. Yours included. I wanted first hand information from dealers and users. So when you say you have witnessed the effectivness of outside combustion in hundreds of installations, does this mean you tried them with and without air kits? sorry it miffed you that i mentioned that your a retailer, but hey, these things cost money and in this debate i dont think a link to a retailer that sells these things is a source. Like i said a few times in this thread, it would take a perfect storm for this to happen, and to think that my customer is the only one out there, is rediculious.(or maybe your suggesting that i made it up) There was a lengthy discussion of this topic and cases at the HPBA classes last spring.

 

[elkimmeg]

MSG I am not defending tim the chimney sweep, but offering common sense to this situation before all is lost trying to win a debate.
Lets start with some premises we all agree hot air rises and that cooler air is heavier? Please explain how ahot a spark can travel threw a cooler air intake. It suposed to be rising and the cooler outside air intake is located at the bottom of the stove? For some reason your novice owners, did not grasp the dynamics of running a modern EPA stove, they concocked stories, that it was the stove or outside air to fault for the innability to opperate it correctly. IF you believe their wide eyeed embelishments, than anything I say further is falling on death ears. You did the right thing by returning them the money and removing the stove. Did they provide any concrete evidence or just hearsay? I telling you what I say?,, from novices that did not know how to opperate a stove?

The question is is outside air needed in a tight house? Any appliance needing combustion will take air from the path of least
resistance. That includes inside air or outside air if available. That fact somehow was missed. Outside air is a supplement to inside air when combustion can not be fullfilled by inside air. Don't believe me then why is the air inlet directed to indoor air? Why not have it to regulate the outside air feed? The out side air feed is supplemental not primary. 2001 International Mechanical codes require provisions for an outside air feed into every fireplace. that's code required. Why? research has indicated that having a super tight home is not all that Healthy. IT like we errored in one way so we have to make it up another way.

Plain and simple MSG you were manuplitated and BS you know it and that's why you started the thread. You were placed in a no win situation and you made the right decision

 

[Roospike]

Im not here to prove anything to you, im hear to open up debate, you obviously think your findings are the gospel on this matter, but you can find otherweb sites that offer the oppisit views. This thread was not started to get links to websites. Yours included. I wanted first hand information from dealers and users. So when you say you have witnessed the effectivness of outside combustion in hundreds of installations, does this mean you tried them with and without air kits? sorry it miffed you that i mentioned that your a retailer, but hey, these things cost money and in this debate i dont think a link to a retailer that sells these things is a source. Like i said a few times in this thread, it would take a perfect storm for this to happen, and to think that my customer is the only one out there, is rediculious.(or maybe your suggesting that i made it up) There was a lengthy discussion of this topic and cases at the HPBA classes last spring.

Again , If this is the case ........ Then we have already had post of owners that have an outside air kit with reports of NO PROBLEMS , NO ISSUES . Any post of owners that have had any issues ? no ? We didnt have any last time this topic came up , nor did we the time before. Its a great topic but i think you are just grasping for straws now. I couldnt even come up with any news storys about outside air kit problems. Hey ! I have a friend that has seen a U.F.O. " sparks and smoke comming out the side of his house when it landed on his roof." Ok ......Its getting a bit silly . BTW Good post thechimneysweep . Thanks for the attachment pic Coaster. Onward. The debate moves forth . Good points all .

 

[velvetfoot]

Well, I know the entire hearth area on my fireplace was darn cold when I had zero clearance fireplace (unused). Does the typical Washington State design have any provision for dealing with this? I remember the fellow from Alaska had outside air coming in to his stove! There must be an optimum design.

 

[thechimneysweep]

MountainStoveGuy:

I don't want to get into a pissing match with you, because I've read some of your posts and I have respect for your experience and opinions. I spoke up here because I perceived an attack on my business ethics, and because I think you're very wrong on the subject of outside air. I want to respond to three points in your latest post:

First point: I did explain why the flashback your customers described can't happen: reread paragraph 5 of my post above.

Second point: I can't find "other web sites" that offer opposite views. As far as I can determine, there is one: a Canadian guy named John Gulland who has a website named www.woodheat.org. I have long since given up debating outside air with this guy, who bases his opinion on the possibility of a backflash that can't possibly happen (see paragraph 5 again), along with a study done in 1989 that didn't even try to determine that outside air was a bad idea.

Third point: You say you were looking for viewpoints from dealers and users, and I am both. I've been a hearth product retailer for 26 years, and have personally burned 62 different woodstoves. On top of that, I've been a Chimney Sweep, an installer, a troubleshooter and dispenser of free advice for the same number of years. The only ax I've got to grind is to get accurate information out to people so they can make intelligent decisions about heating their homes. If you don't want to listen to my opinion, who are you waiting to hear from?

 

[MountainStoveGuy]

No, no pissing matches here. Your points are as valid. It seems that i should start selling OAK's! . I have always been in the netural slot with this subject, some of the posts on here might not reflect that, i was trying to get some debate on both sides of the fence. I realize that most installs are safe, i have a hard time grasping the idea that its impossible to reverse draw through the stove. Thank you for your imput, you must realize the post in reguards to someone not quoting a retail website was not a intentional attack on you, And your opinion stated here by you was a very good post, It would seem this debate is over. I hope everyone got a good education, i did.

 

[tradergordo]

No need to get so heated or personal. I think debate is good. I know I've flip flopped back and forth a couple times already and maybe will again at some point. To imply that someone is on one side of the fence to sell something, or that someone else got conned by a lying customer is just plain mean spirited (and not provable) so lets not go there.

If I have enough spare time, I would love to design a "myth busters" style test for this. We could simulate wind with fans, and a house with maybe a scale size box/shed/aquarium? Have to calculate normal draft in a chimney, and calculate what would be required to overcome that draft with pressure differences and exactly how hard a wind would have to be blowing, etc. A separate issue to test is what can actually be expelled from an air intake in a modern stove. This experiment is actually much simpler so maybe someone here can volunteer to do it (again if time permits I'll do it and make a digital video). Just connect a fan up to the flue of a stove (blowing air INTO the stove) and see what you can blow through the firebox and out the air intake? Maybe start with something simple first like the smoke of a match, and then move to something bigger like a handful of confetti/paper scraps. But all this begs these questions - even if there are no big sparks - is it safe to have 1000 degree hot air blowing out these outside air kits? And if it is safe, would it be safe if even tiny embers were included with that hot air blast? And what materials are being used in the outside air connections? And what would it take to melt those materials? And why apparently are their no code specifications for these materials and how they are connected?


I do think the people who say its IMPOSSIBLE for these $15 outside air connections (are you using the standard thin flex aluminum tube and vents they sell at HD and Lowes typically for dryer vents?) to run backwards have more explaining to do. Yes, hot air rises. This force can be counter balanced by the fact that air is also pulled from high pressure to low pressure. I do not believe it takes extraordinary conditions for this to happen (as implied by chimneysweep) but who really knows without scientific testing?

I wouldn't be surprised if a stiff breeze on the side of the house opposite an outside air kit wouldn't be enough to overcome the natural draft of the stove and get the thing running backwards. And I really do not think MSG's customer made up the story about his outside air connection running backwards but who are we to know? For what its worth, I went to two stove shops while I was shopping for stoves, and of course asked them both about outside air kits. The one store owner just plain told me it wasn't necessary (these modern wood stoves do not use that much air), the other told me he did not recommend them because they can run backwards. That was actually the first time I had heard this, and was what started my investigation. I didn't press for more information from this stove shop, but perhaps I should have.

I think the question is - if it only ran backwards on windy days (which might be one or two days out of the week) and even then, only for 20 or 30 seconds at a time - would it be a safety issue? Probably not in reality. Hence the lack of reported problems.

These designs (images previously posted) that use the outside air connection as SUPPLEMENTAL are actually MORE disconcerting to me than a straight air-tight outside air connection. There is much greater risk from the former of putting noxious fumes and possibly sparks into the actual living space (room the stove is located in) than if it was an air-tight outside air connection where downdrafts would just go outside.

As for healthier indoor air - this is/was probably the biggest concern I had. After reading the chimneysweeponline article I was concerned that not using the outside air connection could leave me living in an oxygen deprived, negative pressure environment. I see the arguments on both sides of this debate but I would think, ESPECIALLY in a tight house, you would actually end up with BETTER, not worse, indoor air quality when you DO NOT use an outside air connection. Why? Because without the connection, you are constantly REPLACING your indoor air with fresh outdoor air, this actually serves to remove stale air from your house and continually refresh it (this is also one argument for using a passive outside air device). This of course assumes that your house isn't so tight that you depressurize it when running the stove. Again, the only way to really know if you fall into this category is by testing. As for efficiency - the cold outside air has to be warmed no matter which method you use (outside air connection cold air is warmed in the stove, cold air seeping in from cracks in the house is warmed outside the stove - both imply a loss of efficiency).

 

[Todd]

As for healthier indoor air - this is/was probably the biggest concern I had. After reading the chimneysweeponline article I was concerned that not using the outside air connection could leave me living in an oxygen deprived, negative pressure environment. I see the arguments on both sides of this debate but I would think, ESPECIALLY in a tight house, you would actually end up with BETTER, not worse, indoor air quality when you DO NOT use an outside air connection. Why? Because without the connection, you are constantly REPLACING your indoor air with fresh outdoor air, this actually serves to remove stale air from your house and continually refresh it (this is also one argument for using a passive outside air device). This of course assumes that your house isn't so tight that you depressurize it when running the stove. Again, the only way to really know if you fall into this category is by testing. As for efficiency - the cold outside air has to be warmed no matter which method you use (outside air connection cold air is warmed in the stove, cold air seeping in from cracks in the house is warmed outside the stove - both imply a loss of efficiency).

Me too. That is why I went with the air supply ventilator. It draws air to equalize the pressure and keeps a small amount of healthy fresh air circulating into the house.

 

[thechimneysweep]

tradergordo, I'm not the mean-spirited type, and wasn't attacking anyone personally. It is pretty hard to respond to a specific point made in a specific post without referring to that poster, wouldn't you agree? MountainStoveGuy has assuaged any rankled feelings I might have had in his gentlemanly post above, and there are no hard feelings.

I am, however, going to kick this horse just one more time, as you bring up some points that bear examination.

Your call for real world testing of the possiblility of OA flashback assumes that there has been no real-world testing, and that is not the case.

With tens of thousands of outside air kits installed in every conceivable weather pattern and wind condition in every area in this country for decades now, there has never been a documented case of outside air flashback.

That's tens of thousands of real world tests, every time the wind blows. Including freak situations you could never hope to duplicate in laboratory testing. For thirty years. Zero flashbacks.

You are absolutely correct, lightweight, uninsulated aluminum dryer vent fittings are approved for outside air delivery to woodstoves and fireplaces. We've been using it since the late 70's, and have no safety concerns with it. Insurance companies have no problem with it, code authorities accept it, and stove and fireplace manufacturers almost universally offer the outside air option without fear of lawsuits. The reason? Tens of thousands of installations have proved that outside air flashback can't happen.

As to the passive nature of many outside air connections at the stove, this is just one of the built-in safeguards that ensure that outside air flashback won't happen. It prevents the extreme suction from the firebox out the intake pipe that would be necessary to pull enough heat or embers through the system to cause a fire, by diluting it with room air.

 

[begreen]

Tom, FWIW I really appreciate your contributions to this discussion. It has been educational. I couldn't understand how stove manufacurers would provide stove modifications to allow outside air unless they were conviced that a) the market wanted this, b) there was a real, tangible benefit, and c) it was safe and reasonably liability free. After all, they have the most to lose.

 

[MountainStoveGuy]

The first thing i did today was call jotul and hearthstone. I havent talked to hearthstone, but i have talked to Jotul. Here is Jotuls position on the issue. Im quoting Mike in the tech department. "there potentially dangerous, there has been many documented cases involving house fires due to out side air kits backdrafting" "the scientific data done by the R&D department shows that there is little to no improvement on overall efficiency or performance" then i asked, then why do you sale them? There responce, "we as a manufacture are boxed in a corner, washington state required them and we dont want to miss market share" "when dealers or customers call here, we absolutly do not recommend them"
I will keep you posted on hearthstones responce.
Ryan

Elk if you have time, can you call VC? or any VC dealer out there, can you get there opinion?