Outside Air Kits, Do you recommend them?

[MountainStoveGuy]

Recently, i have had lots of inquries about outside air kits, i know this has been discussed before, but i thought i would rekindle the discussion. Its my view, that they can be dangerous, expecially in a situation of a poor drafting chimney. I have had customers tell me that they have had smoke and sparks flying out the side of there house. Reverse draw presents a problem with the perfect "storm" exists. ie; super cold chimney, poor desingned chimney, windy conditions, and a new fire. I read sometime back in Hearth and Home that the industry was shying away from them, and the only reason they exist is so they dont miss the mobile home market, which the federal governmet required outside air kits on all stoves. So my questions to dealers and homeowners... dealers, do you sell them and reccomend them? Homeowners, do you have one installed and what do you think it has done to improve performance? Do you think its a valid point that it makes a stove less efficient pulling freezing outside air and having to warm it to combustion temps?

 

[begreen]

This is a good question. We are really tightening up the old farmhouse this summer and I wonder if it's going to be an issue with our 3CB.

My understanding is that in a lot of modern, air-tight houses, there isn't enough combustion air for a robust fire. We've had posters on the forum that couldn't get their stoves working well until they cracked open a window. In that circumstance I would want an outside air supply. If there isn't enough oxygen for a robust fire, how much is left for people?

 

[MountainStoveGuy]

That is a situation that i havent realy come across, i think that scenario is due to a combination of 2 things, to much negative pressure AND a tight house. My house is brand new. I built it myself over a two year span. I have 2x6 walls, blown cellulose insulation, tyvek on the inside and out. Good windows, good doors, etc. My house is tight. I dont have a outside air kit and i dont have any problems. I also dont have many fans exiting the house. Only a bathroom fan, which gets very little use.

 

[Shane]

I agree that negative pressure is more likely a culprit than construction that is "too tight". One thing I've thought of though is that colder air is more dense so wouldn't that be a good thing?

 

[Corie]

I always thought that too Shane. As far as cars go, they operate most efficient when the intake air is coldest so one would think that a woodstove would operate in a similar fashion. However, I've ALWAYS been told that was wrong, but without much explanation.

I guess the secondary part of the equation makes it a little more understandable, since ice cold air will cool the combustion air.

 

[KP Matt]

This always starts lively debates. Personally an outside air kit would be the very last thing I would do. If you need to crack a window doesn't that say more about your draft than your air supply?

Anectdotes abound, I'd like to see the numbers: how much oxygen does a stove require to maintain good combustion, how much air infiltration does a tight house allow, etc. If these houses were really that tight wouldn't you have strange phenomena like ears popping when you open/close the front door? Candles or oil lamps in the other room should noticeably brighten when the front door is opened.

 

[MountainStoveGuy]

Draft, tightness of a home, and negative pressure are all closely related. If you have stong draft, and its pulling hard, that alone creats negative pressure, add a exaust fan thats running, that creats more negative pressure, it the fan creates to much negative pressure it will nutralize the chimney, On the other hand, exaust fans create equalization points in the home when there not in use, wich is why i leave my bathroom doors open. As far as oxygen for combustion, i have no idea, but i can tell you it doesnt take much. The air is thin at my house. If your house didnt have a chimney, or any kind of exaust point except for the attic, i would guess that KPmatt's scinearo would happen.

 

[Todd]

My stove is in the basement and has to compete with the clothes dryer, water heater, and sometimes bathroom fan. I could notice a difference in the burning of my stove when they are all running. To compensate this effect I installed a Condar Air supply Ventilator near the stove and haven't had any problems since. I think it keeps positive pressure in my basement and helps the heat rise to the next floor. Maybe it's no better than an open window, but it's got a filter, and a flapper valve to control the amount of air that enters. Also think a little fresh air inside your home is good to have in the winter months.

 

[HarryBack]

my 2 cents:

I mostly sell pellet stoves, so my comments are thusly skewed. I like outside air. In a closed system. For instance, outside air, vented thru the sidewall, with the pellet stove vented out thru the sidewall as well....NOT the chimney. Most intakes should have a damper as well, hopefully negating backdrafts. Also, these days, most quality pellet stoves have vac switches that will eventually shut the stove down if it doesnt sense normal operating pressures. Tight homes are common around here, and when a customer calls complaining that their stove isnt throwing heat, the last thing they are going to beleive is that its THEIR home thats the issue...they figure that you are a shyster and are trying to find reasons why its their fault as to why the stove isnt heating well. Good Luck winning THAT argument. If theres an intake on the kit, that takes THAT variable out of the equation.

 

[MountainStoveGuy]

Taking that varible out of the equasion could potentially burn the customers house down in the case of a wood stove. As far as outside air to a pellet stove, i still believe that that dont run as efficient sucking in 10* air for cumbustion, there is no pre heat on a pellet stove, at least in the case of a wood stove the air gets pre heated, so by the time it gets it gets to the secondary burn chamber its hot, the argument there is that the cold air brings the over all temp of the stove down and doesnt get as complete combustion as it would if it was sucking 60* air. I hear you that customers dont want to hear that there house is broke, but sometimes, no alot of times thats the case, expecially in these modern tight homes with there commercial kitchens with overhead range hoods that suck 500cmf of air out of the house.

 

[Roospike]

This is my thought .... If your central gas heat system has to be installed with guidelines as per so much air per room size it is in , # of other units sucking the same air ,, bla . bla . bla . Then you would think a wood stove , coal stove , pellet stove would have be the same. ELK on isle 1 please , ELK ... Isle 1 . We need to get the Elk man in here in this subject . When i installed a new fernace in our last house the area of the gas furnace had to have so much inlet air and had to be insuch a way . Just something to think on . I was also told / or i read that if you use no inlet air supply then its draws air through any crack in the house it can find as per the stove has to cycle so much air an hour . On the other hand with a fresh air supply your homes hot air would be pushed out any cracks the house might have . In short the air cracks in the house are not going to go away but at lease its pushing hot air out on not cold air in .

 

[Roospike]

(broken link removed to http://www.chimneysweeponline.com/hooa3.htm)

 

[Roospike]

(broken link removed to http://www.chimneysweeponline.com/hooa.htm)

 

[suematteva]

Roospike thanks for that post best explanation that i have heard.

 

[MountainStoveGuy]

I dont think a web site is the definitive answer on this subject, expecially a web site that retails hearth products. A outside air kit is a nice $100 add on in some cases. Most gas furnaces that require outside air are located in basements, where negative pressure is prevelant. Gas appliances that are getting reverse draw emit carbon monoxide,wood stoves emit carbon monoxide and smoke. You can at least smell the smoke and know you have a problem, on the other hand, when you get smoke coming out side of your outside air supply, you may or may not notice. It sounds like the web site hasnt had a problem with it, i tell you i have, only twice in ten years, but hey its happened. I havent heard any one speak up yet and tell me how much they love there outside air kit. If you do please post. Im looking for personal experences here, weither you a hearth dealer or a consumer. Not web site links.

 

[elkimmeg]

To outside air or not to outside air that is the question Without loosing everbody after the first few sentences the answer is yes and no. First lets stick with wood stoves The formular to calculate the amount of combustion air from free flowing interior space is 1000 btu requires 50 cubic ft. IF competing appliances are in the same space like clothes dryer 150 cfms removed, fuel fired hotwater heater furnace then wood stove all in a cellar none are working effeciently What can happen is one appliance can cause the adjacent one to backdraft. Air has to come from somewhere the furnace can backdraft the hotwater heater or the dryer can backdraft the furnace
Backdraft is pulling co and co/2 into the living space.

Deffinition of free flowing air space is a room or rooms that air comunicates freely to make up the vollume. Doors to adjacent rooms.. those rooms can not be considered free flowing due to the door being able to be closed unless it is a louver door

Woodstove not in the cellar in a very tight home: In Canada outside air kits are not an option but required.
How effective are they? Well pressure nutralization has been mentioned. The problem is the wind does not come from the same direction at all times. If one looks at what hapens when wind hit a home, it produced a positive pressure where it first makes contact.. For simplicity, the front of the home, as it hit the home, it is redirected all around the home up left right leaving a negative pressurization on the opposide of the home,where it first made contact.

Ok now you have the principle down where do you place the outside air feed? which side? Remember wind does change directions
An outside air feed on he negative side will draw air from your fire defeating its purpose. This theory was presented by Daneast or downeast a former member to this forum. It was his contention to split the system and run feeds to opposite sides

Remember a woodstove is not an induced combustion, therefore a weaker draft system then burners or hotwater heaters.
The location of outside air feeds for induced combustion is less of an issue. Air will be drawn in to those appliances. Really the outside air feed should be connected to the burned head of combustion chamber.

When there are competing appliances in close proximity, it is best to feed the largest induced appliance first.

I purposely stayed away from quoting code but there are vollumes that address these issues. Again in the case of a wood stove with one outlet there can be a 50/50% chance the feed produces a negative effect. But when the house is so tight even one inlet might make a difference.

I know I did not do the topic justice so as replys come in, maybe I can explain it better

BTW spent the Day on Block Island. Me and the wife had a real good time we biked atleast 25 miles. What a happening place

while most were in the 90's we got to about 80 all the cooler ocean water around us 15 miles out in the sea.

 

[KP Matt]

I don't think Canadian code has required outside air kits since 1995.

(broken link removed to http://www.wettinc.ca/WETTinkWinter2005.pdf)

The section has been completely rewritten to reflect a shift away from requirements for the supply of outdoor combustion air towards rules for managing house pressures or the consequences of smoke spillage.

WETT is a/the Canadian non-profit wood energy training and education association; as I understand it their pronouncements are based on the relevant national (Canadian) building code.

The idea is that outside air at best doesn't work, at worst can be dangerous, and the real solution is to design building systems better or make them more intelligent.

 

[elkimmeg]

I am familliar with Wett but thankls for the link and review. USA and Canada codes are simmilar as both reconise EPA
One builder in my area does install mechanical venting systems in basements. I have said many times this forum are my educational
renewal.

Unfortunately they only addr5essed wood stoves in the 4 page link and did not really get into outside air direct connections to other appliances

 

[velvetfoot]

I too am thinking of adding outside air, only to the oil burner heater (chimney) in the basement of my 3 year old house. The kit that Burnham sells has a negative pressure relief damper that opens to the inside room air if the outside is blocked. I am adding a radon fan in the basement, at some point, but they are the only two air consumers in the basement. I did notice the kitty door in the basement wouldn't close in the winter because of the stack effect and I had to add some weight. I also noticed that the air mixing damper (or whatever it's called) on the burner flue had a tendency to flap open even when the burner was off: that's not supposed to do that, I don't think - perhaps it needs some adjustment. Anyway, the prefab fireplace on the first floor had some kind of outside air arrangement. It couldn't be turned off. It was QUITE cool around the fireplace, which was remedied by blocking the inlet on the outside of the house. The insert we got was not connected to use outside air; the installer said they've never done that.

I am nervous about adding outside air to the oil burner...

I did add CO detectors on all levels. They make combo units that I was able to retrofit to existing hardwired smoke detector system very easily.

 

[Chuck Pearson]

<<any one speak up yet and tell me how much they love there outside air kit.

I love the outside air kit on my wood burning fireplace insert. I have had it since the fireplace was installed. I would rather have the cold outside air cooling the fire than have the cold outside air cooling me as it is sucked through cracks in the house. I like keeping the warm house air in the house instead of feeding the fire with it. I like the smoke going up the chimney instead of being sucked into the house due to negative pressure. Wind on the side of the house could create negative pressure but it would have to be very high negative pressure to overcome the draft of a good fire. The laminar effect near the wall surface will reduce the negative pressure anyway. My inlet is on the west side which is where winds come from most often.

I also love the outside air kits on my gas furnace and on my gas water heater.

 

[Roospike]

I would say that the only people that can answer this question(s) are the people that have actually used them . The pro's or the cons of how they work . Everybody else is just going off what they have heard or have read. ( my self included ) Based on common sence i can give my opinion like every one else. As Chuck Pearson has stated with his own experence , and what would make sence. The fresh air has to come from somewhere.

 

[tradergordo]

Roospike thanks for that post best explanation that i have heard. (referring to chimneysweeponline link)

I thought so too at first (a while ago) after reading that site. It made sense. I was dead set on getting and installing an outside air kit. There is one problem though - they are wrong. This can be (and has been) tested scientifically. The benefit of providing a supply of outdoor air to wood stoves is not supported by research results.

Please read (broken link removed to http://www.woodheat.org/outdoorair/outdoorairmyth.htm)

Also note that even though chimneysweeponline was confronted with this report, and they even comment on it, they show a lack of understanding of the problem. The issue is negative pressure - this is not caused by down winds (to your chimney) as chimneysweeponline seems to imply. Nor can it be fixed with an anti-down drafting chimney cap. Negative pressure forms when ANY sufficient wind at ANY time blows against the side of your house opposite the outside air connection. We are NOT talking about wind blowing straight down your chimney (which is a problem that can be corrected with a better chimney cap). The negative pressure formed near the outside air termination can cause air to come down your chimney through ANY opening regardless of the type of chimney cap you have.

Read the report I linked to above, it gives all the details. In general, fireplaces that are vented by natural chimney draft should draw the air for combustion from the room in which they are located. Where necessary the indoor air pressure should be controlled to minimize depressurization.

 

[velvetfoot]

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

 

[MountainStoveGuy]

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.

 

[tradergordo]

Here's more from another reputable source (A Guide to Residential Wood Heating - written and distributed by a branch of the Canadian government):

Does Outdoor Air Reduce Smoke Spillage?
It has been widely believed that you could reduce or eliminate smoke spillage by supplying outdoor air through a duct, either directly to the appliance's combustion chamber or indirectly to the room in which the appliance is located. However, research shows that outdoor air supplies may not work. Smoke spillage occurs at the same level of room depressurization, whether or not an outdoor air duct is installed. The same research shows that wind effects around the house can reverse the flow in these ducts, which may create a fire hazard if the duct is connected directly to the combustion chamber.

Some building codes require that you provide wood-burning fireplaces with outdoor combustion air. You must comply with this requirement, but be aware that performance will not improve. And take steps to protect combustible materials around the duct from overheating if the gas flow reverses.