OAK inlet has to be below stove?

[Knots]

I was just thumbing through the Jotul F55 manual in preparation for building a new house. I noticed that it said that the OAK inlet should not be above the stove inlet.

This stove is going to be in the basement, and I was planning to run the OAK through the rim board, but now it looks like I'd better rethink it. Any suggestions?

 

[TheBean]

Consider a passive air intake close to the stove? Might be a good solution to a basement install that needs outside air. Lots of options out there. Dare I say, Google it.

 

[bag of hammers]

I noticed that it said that the OAK inlet should not be above the stove inlet.

I am curious - is that because the higher-up OAK potentially can start to draft (and become a "chimney")..? Can somebody explain? Sorry if this should be obvious

 

[Knots]

Consider a passive air intake close to the stove? Might be a good solution to a basement install that needs outside air. Lots of options out there. Dare I say, Google it.

Passive intake? I'm not sure what that is. The house is going to be tight so outside air will be required somehow.

 

[Knots]

I am curious - is that because the higher-up OAK potentially can start to draft (and become a "chimney")..? Can somebody explain? Sorry if this should be obvious

It's not overly obvious to me.

 

[bag of hammers]

It's not overly obvious to me.

I don't get it but some of the folks on the forum have a really deep understanding of the physics behind wood burning in just about every situation / setup. Just thinking that this OAK height limitation may be no surprise to them and they could enlighten us...?

 

[BrotherBart]

Actually the first time I have seen that. But it is entirely possible that natural draft could set up in an OAK higher than the stove. Especially in a basement install with chimney effect being what it is and low pressure in any house being in the basement. The negative pressure pulls air down into the basement since it is drawn up in the rest of the house. Happens with my chimney on the stove in the basement.

 

[superbee69]

I don't get it but some of the folks on the forum have a really deep understanding of the physics behind wood burning in just about every situation / setup. Just thinking that this OAK height limitation may be no surprise to them and they could enlighten us...?

My basement plan for a super27 will have the oak inlet about 14" above the floor where the stove sits. I too wonder how effective or ineffective this will be. My piping will come in at 14" high, drop down to below the built up pedestal, then the air feeds to the super27 under the pedestal of the stove.

 

[Knots]

I don't get it but some of the folks on the forum have a really deep understanding of the physics behind wood burning in just about every situation / setup. Just thinking that this OAK height limitation may be no surprise to them and they could enlighten us...?

The rest of the manual is pretty good and explains the reasoning behind things but on this they just have one sentence. I can speculate a lot of different possibilities but don't have confidence which it is.

 

[TheBean]

I believe the concern is the oak duct acting as a chimney if there is a draft reversal. Obviously that duct is not designed to handle flue gas temps. Some passive intakes offer adjustable flow rates and may also offer some flexibility as far as install location. Link for a basic example. (broken link removed to http://www.conservationmart.com/p-537-therma-stor-fresh-80-passive-air-inlet-4018819.aspx?gclid=CMHy3dCCorYCFVKf4AodoDwAJA)

 

[bag of hammers]

I believe the concern is the oak duct acting as a chimney if there is a draft reversal. Obviously that duct is not designed to handle flue gas temps. Some passive intakes offer adjustable flow rates and may also offer some flexibility as far as install location. Link for a basic example. (broken link removed to http://www.conservationmart.com/p-537-therma-stor-fresh-80-passive-air-inlet-4018819.aspx?gclid=CMHy3dCCorYCFVKf4AodoDwAJA)

That's kinda where my brain was going but it would have been just a guess on my part. Thanks BB and theBean for sanity checks. Interesting link (I have a Thermastor dehumidifier in my crawl space) ...

 

[westkywood]

I have the Super27 with an OAK. I have mine run through the wall just above the baseboard. It actually is just a tad higher than the inlet. No negative affects...

 

[Knots]

I believe the concern is the oak duct acting as a chimney if there is a draft reversal. Obviously that duct is not designed to handle flue gas temps. Some passive intakes offer adjustable flow rates and may also offer some flexibility as far as install location. Link for a basic example. (broken link removed to http://www.conservationmart.com/p-537-therma-stor-fresh-80-passive-air-inlet-4018819.aspx?gclid=CMHy3dCCorYCFVKf4AodoDwAJA)

Thanks for the link. I'll have to take a look at these.

 

[WidowMaker]

Passive intake? I'm not sure what that is. The house is going to be tight so outside air will be required somehow.

=====

Isn't that just a $10 phase for "hole in the wall"???

 

[blwncrewchief]

It is a possibility to reverse the draft if a fluke happens with an OAK located higher than the stove. The options to stop that from happening would be a passive intake where it is piped close to the stove but not hooked directly to the stove or another option if concerned about a reverse draft with an OAK is to use a backdraft damper such as this:

http://www.amazon.com/Speedi-Products-AC-BD-04-Galvanized-Prevention/dp/B0085UZDA4/ref=sr_1_8?ie=UTF8&qid=1364701829&sr=8-8&keywords=back draft damper

 

[Ejectr]

So what you're saying is with my PF100 furnace sitting on the basement floor with the air intake about 18" off that floor surface and my house's sill being about 7 feet above the air intake....that is a no no? There's no other way to do it.

 

[begreen]

=====

Isn't that just a $10 phase for "hole in the wall"???

LOL, no, it's a hole in the wall with a bug screen and a rain hood.

 

[bag of hammers]

LOL, no, it's a hole in the wall with a bug screen and a rain hood.

I guess the woodstove industry is no different than others - take 2 or 3 parts worth $5 each, throw them in a box, call it a "kit", and retail it for $50....

 

[Knots]

After scratching my head and talking to some people, I came to the conclusion that people here did. The risk is the inlet acting like a chimney.

I reckon that this is unlikely to happen, but that under some weird combination of winds could happen.

I finally came to the conclusion that if the inlet had a T and an inlet from both the front and back of the house fed that T before going to the stove, that it would be difficult for a reverse chimney to happen. So, I'm planning on putting two inlets through the rim board - one in front and one in the back.

 

[mellow]

Wonder if that would create a wind tunnel?

 

[Knots]

Well, I'll have to see about some possible flappers near the T to prevent that.

 

[DexterDay]

No ill effects with an OAK on my basement stove? Its not a PE unit? But its about a 6ft rise?

 

[bag of hammers]

I wonder how badly a chimney would have to be plugged / pooched / etc or what kind of weird winds you could have to be experiencing for the OAK to actually start to compete with the chimney (and win)...? I don't know if that even makes sense, but looking at Dexter's setup, my first reaction is "nothing wrong with that" - a very nice install, IMHO.

In a way, I might actually even be a bit more comfortable with a setup like that (where the OAK is up higher, but everything is neat, up front, visible, accessible) than I am with my setup (OAK is under the pedestal, runs under the crawl space, 100% completely out of sight). Maybe that's just a silly perception thing...?

An interesting discussion either way. The Jotul guys should really provide some documentation around why they spec this out this way, to keep all the inquiring minds happy ...

 

[DoubleClutch]

I finally came to the conclusion that if the inlet had a T and an inlet from both the front and back of the house fed that T before going to the stove, that it would be difficult for a reverse chimney to happen. So, I'm planning on putting two inlets through the rim board - one in front and one in the back.

Good God, I think you're overthinking this just a teensy bit.

I would just bag the idea of an OAK. They're pretty much pointless, anyway, unless your house is as airtight as the vacuum chamber in a Thermos bottle. (And no house is, or should be.)

Why?

1. If you pull outside air into the stove for combustion, the amount of heat you get out of the stove will be reduced compared to the amount of heat you could get out of the stove if you used "inside" air for combustion air.

2. By how much would that amount of heat be reduced? It would be reduced EXACTLY by the Δt (temperature differential between outside air and inside air) x (number of pounds of air per hour consumed by the stove.)

3. In other words, all other things being equal, in order to get as much heat out of the stove using outside air as inside air, you must FIRST heat the outside air to the same temperature as the inside air. (Hint: That's exactly what happens when air is drawn in through all the cracks and tiny holes in a house to replace the air that goes up the stack.)

4. In other, OTHER words: It's a wash. You'll get no more efficiency from the stove, in terms of how much heat you can extract from it, using outside air as inside air.

5. More importantly, you MAY reduce the COMBUSTION efficiency of the stove by introducing combustion air that is too cold, if you use outside air.

So before you go spending $10K designing NASA rocket-surgery plenums and intake manifolds ... I would advise a dose of common sense...

 

[Knots]

The house is gonna be pretty tight - so I think it will be an issue if I don't use an OAK. I guess some experimenting will be in order.