Outside Air Kit in non-airtight house. Does it make a difference?

[kalevi]

Perhaps one of the experts could step in here and answer the questions from the topic of the thread?

Leaky house, you get outside air for the combustion anyway. Use a OAK in leaky house, probably not much benefit 'cause your house leaks a lot anyway.

Air tight modern house, you need some inlet of outside air or you get negative pressure. OAK into combustion chamber or just air inlet somewhere so you use warm room air for combustion and replace with cold outside air. How much efficiency loss do you get?

 

[bokehman]

Lets look at it from a scientific perspective, when you burn wood for every pound of wood consumed you need about 8 pounds of air for efficient combustion in most wood stoves.

How much wood you burn has little to do with how much air goes up the stack. The two factors controlling that are the depression in the stovepipe and the size of the restriction.

One thing you can be certain of is you are venting a lot more air than is necessary for combustion.

Now, just like in an internal combustion engine, the colder the air you feed it the more power it puts out. The leaner you run it the hotter the combustion.

A lean motor doesn't run hotter because it is lean; it runs hotter because there is not enough fuel to keep the combustion chamber quenched. Also if you ask a lean motor to produce real horsepower you'll end up with a hole in a piston within a few cycles. And we're not talking a lot lean; the stoichiometric point is about 14.8:1, running a motor at 14.9 or 15:1 under heavy load would be enough.

 

[danielsonrose]

I just installed an outside air kit to see if it would help in my application. I have the stove in the basement and have had some difficulty. After installing it yesterday and monitoring the temperature in the stove and the in the house and reviewing burn characteristics I can say the outside air has helped noticebly. I can't explain it but it works in my application. The stove heats up quicker and gets secondary burn faster and also the heat is transferred upstairs better. I woke up this morning and the house was at 67 and normally with the weather near freezing it is between 62-64. My house is newer construction and the only thing I can think is that it has helped equalize some of the pressures in the house. Anyway, it seems to be working in my application even though I can't really explain why.

 

[TMonter]

http://www.woodheat.org

The fallacy in their approach is they're not calculating it with the fire and draft going. A properly sized OAK is going to automatically bring air in provided the flue is hot and drafting.

The colder combustion air may cause you to lose your secondary combustion, or even make the wood start to smolder, despite the fact that the colder air contains more oxygen for a given volume.

Very unlikely given the small number of BTU's for a less than 100 degree temperature difference between outside and inside air.

 

[TMonter]

There is a significant difference between 77 and 969 BTU to heat 8 lbs of air, right?

Doh! You are correct, this is why I usually don't do the math in my head. I was swapping units I shouldn't have been. Good catch. Fixed it.

 

[TMonter]

How much wood you burn has little to do with how much air goes up the stack. The two factors controlling that are the depression in the stovepipe and the size of the restriction.

I never claimed that it did but you do need more air than stoichiometric with solid fuels. Average for firing wood in most stoves is about 8 pounds of air to 1 pound of wood.

 

[Hogwildz]

Just get a turbo with a charge air cooler, that'll pack the cold air in with plenty of pressure psi.

 

[Rockey]

A lean motor doesn't run hotter because it is lean; it runs hotter because there is not enough fuel to keep the combustion chamber quenched. Also if you ask a lean motor to produce real horsepower you'll end up with a hole in a piston within a few cycles. And we're not talking a lot lean; the stoichiometric point is about 14.8:1, running a motor at 14.9 or 15:1 under heavy load would be enough.

The lean motor runs hotter because all the fuel was completely combusted and none was left over to cool the spent gases. it may have been a bad analogy on my part to compare it to a stoves combustion with wood fuel.

A hole in the piston is only one of many possible results of detonation/preignition, depending on many factors including engine design. A lean condition is also one of many factors that leads to detonation/preignition and results in the carnage you described.

 

[Rockey]

Just get a turbo with a charge air cooler, that'll pack the cold air in with plenty of pressure psi.

I'm with that guy. Intercooled turbos are a great way to make power.

 

[rotarysound]

I was operating under chimneysweep's WA State interpretation but it is apparently not that cut and dry.

I called to talk to my installer/dealer about this because I am having a Jotul F3 CB put in next Friday and was hoping to discuss the wall or floor opening for the OAK. Well, the dealer said that an OAK is not part of my installation job because I have an older stick built house and that it's only required for New construction and Mobile and modular Homes.

I was fully expecting an outside air system from the initial install inspection, discussion and having told the guy that despite my house being older it was remodeled and passed the blower door test. I could have sworn I heard the guy say that he would include one then.

Go figure.... I am not a building or fire code expert, I have to defer to the professional installer's interpretation.

http://www.woodheat.org has a page which is highly negative on outdoor air:

But as mentioned in the Chimneyseep's post above, Washington State apparently mandates ALL wood/gas stoves, fireplaces, burning units be connected directly to an outside air source.

So, maybe that makes your decision for you?

 

[Jefflee1]

I have been following this debate for a while. I have done a lot of searches here and other websites to find different opinion's. I have a house that was built in 1820 something with a couple addition's on to it, and yes it is drafty. I am pondering putting a OAK in to see if there is any diffrence. Here are my thoughtss on the subject.
As far as air being denser in the winter time I will agree with that, but I don't think you will see a improvement in efficiency either. On air temp, you are heating the air too 1100 degrees anyway, the 50-70 degrees difference I don't think will really make any difference, it is something like 8.87% more .. I like the fact that I will have LESS air comming through my Cracks in the winter time. For the $60.00 and the couple hrs time, I think I am going to try it.. what the hell, I have a 2200.00 stove 1600.00 worth of chain saws, numerous mauls and axes.
If it works, great if not, I will take it out and burn just like I am doing this year.
I also think we can go back and forth if it does or doesn't work, but I would listen to the people who have them and/or have tried them.

Jeff

 

[Highbeam]

" I have to defer to the professional installer's interpretation."


False. You do NOT have to defer to the installer's interpretation. You HAVE to defer to the inspector's interpretation who will reject or approve the work of the installer. In Pierce County, just north of thurston, my old 1963 stick built house was required to use OA or it would have been rejected by the county building inspector. I asked.

If you are not sure then get the word right from the building inspector. I believe that the installation will be safe and functional whether or not you use OA but the inspector is the only one with authority here.

 

[thechimneysweep]

Rotarysound, here's the scoop:

Washington State's original intention was to mandate outside air in all new installations in newly constructed houses, due to how tightly they are built today. Outside air was already required in mobile and modular homes for the same reason.

The eventual wording of the law, however, calls for outside combustion air in all new installations, period. Most counties in Washington State interpret the law as written, and require outside air in all new installations. A couple of counties, notably King county, have chosen to enforce the law as originally intended, and only require outside air in newly constructed houses. Forum moderator BeGreen lives in King county, and wasn't required to install OA for his woodstove in his existing house in that jurisdiction.

It could be that your county has sided with King county, and won't require outside air in an existing house. A call to your local Buildings & Codes Dept. will determine that for you.

 

[rotarysound]

I called the City of Olympia Building Department today and near as I can tell, my installation will not require outside air. The official explained that the interpretation is based on age of the home in most cases. In my case, it's an old 1936 home and some of the walls (the stove wall) have no insulation. So I expect that the inspection will pass.

I really appreciate your experience and guidance on this.

Highbeam wrote: If you are not sure then get the word right from the building inspector.

thechimneysweep wrote: It could be that your county has sided with King county, and won’t require outside air in an existing house. A call to your local Buildings & Codes Dept. will determine that for you.

 

[Galroc]

One thing I need to mention is most have other appliances that need air, like a furnace or a stove vent.

In my case, I have an oil furnace. I also have a 1200CFM hood vent that will dwarf anything a pellet stove can do, which I think is about 10cfm max.

So, I think I will go with an outside air kit for my pellet stove so that it isn't affected by our stove vent, even if it already has a source for outside air.

 

[kalevi]

The efficiency question is how much loss do you get if you burn room air (because you draw warm air from house which is an energy loss because it is replaced by cold outside air through leaks in the house) as opposed to drawing outside air directly to the stove? Does it make a significant difference?

 

[pcampbell]

I think I am going to go for a OAK. I call it a CAI because I am a car guy I believe I've read from more than one stove manufacturer that the stove is more efficient burning cold air. It seems like a no brainer if it is not inconvenient to install.

One thing I am wondering is if I should go down, or out. Down is my garage and is by no means sealed. Sounds sort of ghetto, but it may be less conspicuous looking on the install Out requires a little more penetration and care because my cable and electric wires are all coming into the house right on that wall.

 

[Highbeam]

A garage full of cars, gasoline, carb cleaner, and other such things is not a good place to take combustion air. I would go out.

 

[pcampbell]

Great point. I hadn't thought of this. We do not store any flammables in the garage (since it is attached, we put all the junk in the shed way out back), BUT, we do park the diesel car in there from time to time.

 

[Highbeam]

I painted a car in a garage once. Them fumes were pretty stinky.

 

[hvcompton]

WOW Cold air does not effect combustion. Simply put the air temp is not even close to what it would take to effect performance of a stove. The coals of a stove are above 1000 degrees. The outside air has no chance of slowing down or even reducing combustion temps.

Actually Cold air would raise the combustion temp. Cold air has more oxygen per volume than hot air. With the stove damper closed it would allow more oxygen into the fire than was being pulled from the room. For the same amount of air.

I have also read several post about air being pulled back out the OAK from the stove. If you have any back draft that is close to being this bad. Call for help your stove or chimmley needs service. Loose gaskets and poor installation can cause many puffing and back drafting problems.

Also lean engines makes more power. More heat more power. not less. Performace engine run much leaner than stock. 15 to one will not blow a hole in the piston. It may seize it over time but not right away. 4 strokes are cooled on the intake stroke while the cam is in its overlap state. More overlap the leaner you can run it. Race engines have a large amount of overlap for many reason this just being one of them.

2 Strokes make the best power when they are very lean. They will lock up from the heat but power is greatly increased. It is common for someone to say it was running its best right before it seized with 2 stroke engines.

Sorry for the Rant but I have read this post and wanted to put my to cents in.

 

[jgoodnow]

Just for completeness, here are some references about the use of outside air. It appears that John Gulland, founder(?) of the web site http://www.woodheat.org, is one of the leading proponents of NOT using outside air. This seems to be based on a study done for the Canada Mortgage and Housing Corporation in 1989 called Fireplace Air Requirements (http://mha-net.org/msb/docs/airreq.PDF). The findings in this study resulted in the removal of the outside air requirement from the Canadian building code in 1995.

A few other references:

John Gulland blog writings: http://mha-net.org/msb/docs/outsair.htm
Woodheat discussion of outside air: (broken link removed to http://www.woodheat.org/outdoorair/outdoorair.htm)
The positive case for using outside air: (broken link removed to http://www.chimneysweeponline.com/hooa.htm) and (broken link removed to http://www.chimneysweeponline.com/hooa3.htm)
Canada's A Guide to Residential Wood Heating: http://www.canren.gc.ca/prod_serv/index.asp?CaId=103&PgId=576 (see Chapter 10)

The CMHC study is almost 20 years old, and I haven't seen any references to additional, newer studies. The Chimney Sweep Online articles look like good arguments for using outside air. That said, I would not use outside air unless 1) it was cheap and easy to install, which it isn't in my case, or 2) I was having a performance problem that could be solved by outside air.

 

[bokehman]

Also lean engines makes more power. More heat more power. not less. Performace engine run much leaner than stock. 15 to one will not blow a hole in the piston.

I've been building, dyno-ing and racing drag motors for almost 30 years and I can assure you that lean motors do not make more power and that once you get into the 300bhp/litre range with 15:1 mixture you will end up punching a hole through a piston in as little as 5 cycles.

 

[billb3]

Just how cold is this outside air going to be by the time it gets into the firebox ?

Is everyone running nitrogen cooled tubes ?


The condensation running off the tubes must be ruining everyone's floors.

 

[Highbeam]

Just how cold is this outside air going to be by the time it gets into the firebox ?

Is everyone running nitrogen cooled tubes ?


The condensation running off the tubes must be ruining everyone's floors.

I've made it a habit of feeling my tube (OMG!) for temperature when it is really cold out just to verify that I am sucking cold outside air and that it really is working. The tube is always colder than room air but never cold enough to condense water. Probably due to the 25% RH in the stove room. The single pane windows seem to be much colder and easily collect condenstion in adjacent rooms.

To be honest, I feel the chimney pipe too for heat so I am a tube feeling fool.