Outside Air Kit: To Do, or Not To Do

I have done some research on OAK 's and the validity of installing them and see many conflicting opinions and articles. The article below pleads a pretty good case against them, unless required by code of course.

A non-commercial service in support of responsible home heating with wood - The Outdoor Air Myth Exposed

The gist of the article is that OAK is not necessary because the air consumption of a modern wood stove is in the range of 10-25 cfm, which is small compared to natural leakage rate of houses.

If this is true (and I'm sure it is in the case of my 1884 house with very little insulation and original windows) then my Engalnder NC30 shouldn't be creating any negative pressure in my house which could cause cold air to be drawn in from the outside (anymore than is already occurring) or causing draft from the chimney to reverse and pull smoke into the house through any leakage of the stove.

What are your opinions on the OAK debate? Should everybody have one, or only people required to by code?

Before responding, I highly recommend reading the entire article linked above, so we are all on the same page.

 

So, they are saying because it could still leak a little with an OAK it is better to let it leak a lot? Or if it is still possible to get flow reversal with the OAK, you might as well let it reverse flow into your family room?

That’s moronic!

Yes, you need to be careful with OAK placement if exposed to wind and no it won’t solve all problems, but installs that have the downsides they mention are going to be an order of magnitude worse without the OAK.

Also, old houses leak like a sieve. For new build houses that are super air tight, 25 cfm is a material number. I think the general trend is to design tight houses with possitive air pressure now which will prevent any stove leakage problems and will all but eliminate reverse flow risks on a non-oak if sized properly, but using an OAK will still cut down on the load on the makeup air system so I would talk to your HVAC engineer about stove plans if doing a new build.

 

I aay there is no one right answer to the OAK question.
Too many variables...

 

I think they are saying that the amount of air used by a modern wood stove is small compared to the air being leaked, therefore adding an OAK has little effect on reducing the amount of leakage. I have no idea if this is true or not, as I have not yet begun research on how much old vs. new houses leak naturally.

I don't think the article is saying you might as well let reverse flow from the chimney happen, I think they are saying that there is little chance of that happening with or without an OAK, unless you have other devices in the house causing large pressure drops. The lack of an OAK will not be the root cause of this phenomenon occurring.

In other words, if you have reverse flow occurring, you need to be looking into other causes of the pressure drop inside your home, because most likely the biggest pressure drop is not occurring from the wood stove drawing air from inside the house.

I honestly don't know what the actual numbers of leakage are, so I don't know if it is true or not. I just want to make an informed decision before deciding to get an OAK or not, and not just get one just because. I am currently leaning away from it, as the stove is installed this year is performing quite well, and I have no issues with smoke in the house (except a little when first lighting) or with the house feeling more drafty when the stove is burning.

 

One of the more pertinent paragraph's from the article:

"It is sometimes assumed that taking air from outside through a duct saves energy because the stove doesn't use up indoor air and cause outdoor air to be drawn in through leaks to replace it. But the assumed heating deficit is so small as to be insignificant. The average air consumption of a modern wood heater is in the range of 10 - 25 cfm, which is very small compared to the natural leakage rate of houses. Building scientists say that the air in a house must be exchanged at least every three hours, or one-third of an airchange per hour, to control moisture from cooking and washing and to manage odors. One third of an air change in a 1500 square foot house is 4000 cubic feet, or 66 cfm. Note that this is the absolute minimum air change for healthy living and that most houses older than 20 years have natural leakage rates far higher than this in winter. So the air consumption of a wood stove is a tiny part of a much larger exchange of air between the house and outdoors."​

 

I would say unless you've had your 1884 house weatherized there is no way you can put enough air through your stove to compensate for the natural air leakage in the house. This would not be the case and a new energy efficient home.

 

I chose to go with an OAK. I have a home, still not completed, so it will be tight. There is 6" of wool insulation between the 2x6 studs, injected foam around windows and every nook & cranie, caulking between timbers in every built up beam & column, plus 17" of vermiculite in the attic. In addition, the doors and windows were highest energy efficiency I could buy, even having argon between the glass layers. I'm afraid if I inhale, I will create a negative pressure, LOL.
The inlet on the outside is protected from direct wind as the home is in a dense forest.
Is it good or bad? I don't know. But, it's easier to plug it in the future, than to add it later.

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Agreed

 

Not a big fan of airtight houses as I built one, lived in it for 8 years, then moved to a leaky un insulated house for a season. I actually was more comfortable in the leaky house. I remembered that and brought the subject up when I worked for an American energy audit company doing work in Saudi Arabia. There is, more comfort in going into different temp environments according to what they were learning. Right now I live in a home where it's extremely warm in one section and colder in the other. I like going back and forth, as in nature temps are dynamic. Regardless, in both homes I had an OAK. One factor to keep in mind, without one, dryer air comes in, to supply the intake, and that leads to static electricity. So, the question of OAK or no OAK should be brought up with your cat.

 

For even new typical minimum code compliance built homes an OAK probably isn't "necessary" but I see an OAK as one more way to keep your heated air inside the home. Yeah, likely exceptions, but how many and on a case by case basis more generally probably worth the effort. In tiny, supertight builds they probably should be required. Say, under XXXX cubic feet. Over XXXX cubic feet optional.

I did it with my oil boiler in the basement, just because I could .
If I ever replace this tiny wood stove and the new one is capable I might try it with that as well.

 

No. Who needs more holes to the outside in a home ?

 

It is required here by code. But I am glad to have it, as I think it makes sense to not pull air in through leaks in order to provide combustion.

 

I think it’s a good idea. I will install it unless I can’t due to some good reason. If wanted to intentionally create another leak I would open a window.

 

I don't have one, but I would be curious to see if it would eliminate some of my drafty areas near the stove (front entrance, front windows, etc.). It's easy to feel a draft around your feet when sitting on the couch at the other side of the room from the stove.

 

A heater often gets a localized warm air rising drafty circulatory system moving in a room. The circulation and draft is welcome in the Summer, Winter not so much. Warm floors is often advantageous with a basement install stove.

Edit: IMO, the cold ceiling on the graphic on the left is a bit of an exaggeration.

 

OAK mandates were originally for tight mobile homes in most places. Super tight homes yes.
The idea of basement heating is another poor concept unless the "basement" is well insulated. Without insulation you're heating a bunch of foundation dirt IMO.
Wood stoves are basic space heaters where you spend your time...IMO.

 

Soil around a basement wall has R value and thermal mass. Keep that soil as dry as possible and the thermal mass capabilitties increase. Even water can be used for a thermal mass. Soil and water are both used in greenhouses to keep them warm in Winter, some using soil to store the day's heat overnight.
It's usually the basement wall above the ground exposed to outdoor ice cold air that is a tremendous heat loss and ice cold.

 

1/2 right. That "mass" is where much of that local heat will be transfered without insulated foundation walls.
While the mass of any substance can be used as storage, not in a basement...it simple violates thermodynamics in the real world of foundations. The "stored" heat is then outside, not in your body.

 

LOL, you're contradicting yourself. plot your cumulative R values to calculate changes of rates of losses.
When you "add insulation" you're not going from nothing to something, you're going from something to something better.


Earth shelter - Wikipedia

 

No.