Fresh Air Intake Question

I'm just a mason not a woodstove expert.

How is the outside air fed to the upper fireplace?
The units I always used had a outside vent that allowed air into the clean out chase which the fireplace could pick up through a slotted clean out door installed towards the front of the firebox.
With this particular set up you should be just fine tapping that air supply for your basement install.

I've seen other masons bring the air into the walls of the firebox directly with some sort of chintzy round duct vent.
With this type of installation things would get very strange. The air would need to come in around your upstairs insert then travel down through the clean out.

If the existing vent can provide enough air, it might work. OAKs are not supposed to have an outside termination higher than the stove according to the Hearthstone manual with my stove, however members on this forum seem to have done it successfully.
"The International Residential Code (IRC) does not allow the outside air duct to terminate higher than the appliance. Some building officials also do not like to see any vertical rise in the duct’s termination."

DougA said:

If the existing vent can provide enough air, it might work. OAKs are not supposed to have an outside termination higher than the stove according to the Hearthstone manual with my stove, however members on this forum seem to have done it successfully.
"The International Residential Code (IRC) does not allow the outside air duct to terminate higher than the appliance. Some building officials also do not like to see any vertical rise in the duct’s termination."

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Think of it this way. If you have an OAK higher than the stove you basically have an extra chimney that comes in near the bottom of the stove. On my own OAK I was even concerned about a loop I had to have in mine that meant air had to travel down a bit before it returned above the outside connection. I finally came to the conclusion that it would not act as an inadvertent chimney because I had insulated it well, so I could treat it as a constant temperature system and it would be entering below where it would exit to my stove.

Skitheeast said:

Jo191145 - Thanks for the response.
Yes, our set up was exactly as you stated above. b/c we installed the insert, and sealed the slotted clean out door towards the front of the firebox, I figured that the clean out chase could serve as the fresh air intake due to the outside vent on the exterior of the masonry chimney.
The only concern would be that the two clean out chases weren't sealed off from each other, which I hope isn't the case. As a mason, Is that standard practice to make sure the 2 clean out chases are separate ?

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Yes, it is mandatory the two clean out chases be separated.
Of course I can't guarantee from my couch whoever built your fireplace did so but it is code. It should be easy enough to tell by opening the clean out door for the basement flue. You should see an interior wall on each side. Should be a narrow chase 8- 10" wide.
Perhaps a drop light inside one chase and observing for visible light in the other might be in order.
You do have two clean out doors correct?

DougA said:

If the existing vent can provide enough air, it might work. OAKs are not supposed to have an outside termination higher than the stove according to the Hearthstone manual with my stove, however members on this forum seem to have done it successfully.
"The International Residential Code (IRC) does not allow the outside air duct to terminate higher than the appliance. Some building officials also do not like to see any vertical rise in the duct’s termination."

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Interesting point. I can understand the reverse chimney theory. I'm not familiar with the codes on this subject, been out of the fireplace business for awhile now. I can remember building only one basement fireplace since the introduction of mandatory supplied air. Right or wrong I fed it air.

Couple months back I was perusing basement installed wood furnaces on the web. Going to be replacing my entire heating system soon. Anyhow there was one site that had the specifics on how to install outside air. All of them included an outlet exiting through the joist area. I recall they all used a trap system much like oldaman47 describes. Wish I could remember which site that was on.
I would think a masonry chase the OP and someday myself are considering would be better/safer than any piping system. Less chance of creating a draft and if the unlikely did happen it's masonry not wood. I can't fathom any smoke traveling through that chase, exiting through that small grill to the outside and creating a fire. Maybe if one is using gasoline for a fuel
I am glad you brought this to our attention though. It's something to learn about.

And then there's this. I'm not advocating one way or the other on the validity of this article.
http://www.woodheat.org/the-outdoor-air-myth-exposed.html

An old crazy thought I once had just came floating back. Any laws against tapping into the footing drains for air supplies?

Jo191145 said:

And then there's this. I'm not advocating one way or the other on the validity of this article.
http://www.woodheat.org/the-outdoor-air-myth-exposed.html

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I've read this a few times and strongly disagree with much of the article, especially this: "A stove vented by natural draft needs a reliable and unrestricted supply of combustion air. Since passive outdoor air supplies in reasonable sizes are ineffective and since direct combustion air supplies are unreliable and potentially dangerous, other options must be considered. The most obvious alternative is to take combustion air from inside the building"
The only concession I will make is the following situations: if your OAK has a long run; entry point much higher up from the stove; is situated where the inlet may be subject to excess pressure/depressurized from a poor outdoor location. I've also stated many times that adding an OAK in a non-airtight house may not make a lot of sense.

My installation has a 2.5' horizontal run from the outside wall and I am VERY HAPPY with it. I have a newer, air-tight home and if there is any problem at all, my system has more draft than I would prefer. I specifically located the new stove where I had easy access for an OAK. My old stove did not have an OAK and I had regular problems with backpuffing.
An OAK is not the answer for everyone but in my case, it works.

In the case of the OP, it probably is best to run a flexible hose and see how the stove performs before spending a lot of time doing a proper installation.

bholler said:

I don't know but i don't think it is a great idea

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Buzzkill

Granted I can see moisture during the off season wreaking havock inside the stove.
I can see improperly laid footing drains being full of water and not allowing air through.
I can even fathom underground gases be they induced by nature or man being a concern.

Anything else I'm missing?

Jo191145 said:

An old crazy thought I once had just came floating back. Any laws against tapping into the footing drains for air supplies?

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No laws I have heard of but look at the vents on your footing drain. I have 3 of them at 2 inch diameter each. The vent goes through your heated space so it will draw nicely, just like your chimney. Unfortunately you do not want your fresh air supply to come from an area that is under a low pressure like a chimney. It is intended to provide makeup air for the air you are burning and you don't want to have to fight for that air. I have a partially built OAK and will wait and see how it goes before I punch through the outer wall in a more or less neutral location. In my case the prevailing winds are pretty much from the west with a slight angle from the north. My OAK penetration location is on the south wall near where it meets a north / south wall. That means that on a windy day it might have a bit of pressure from the wind but normally it will be very neutral.
Like DougA I consider that stuff on another location as at best suspect and at worst misleading. It basically says that I can't take prevailing winds into account so I am doomed to have my OAK be ineffective.

It would seem that a simple one-way damper on the outside air supply would prevent any "chimneying" effect.
I don't understand the physics behind needing to have the fresh air intake at or below stove level.
Our natural convection, direct vent gas stove has the air inlet and exhaust outlet at the same height 25 ft. above the stove. How is that any different?

If your house is too tight you may want to install a source of fresh air anyway using an HRV or ERV. Then that system could be biased to provide makeup air for the stove. Just a thought.

semipro said:

I don't understand the physics behind needing to have the fresh air intake at or below stove level.

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Under certain conditions, the OAK can actually air into it and act as a chimney. This is outlined in the link posted above and I copied it again here: http://www.woodheat.org/the-outdoor-air-myth-exposed.html
As I posted earlier, I disagree with much of what is stated BUT I do agree that an OAK can cause a problem and should be used only when proven necessary. Also, there are plenty of members here who have OAKs that go from the basement to an outside outlet much higher that seem to be quite happy. A gas stove or a gas fireplace is a different animal. Many of us have experienced things happen with wood stoves that can appear to be 'out of control' and it's obvious that installations of identical wood stoves in different homes can be quite different in operation.

Skitheeast said:

Hi everyone,
So I hooked up the oak this past weekend and the same thing happened. The fire slowly went out when the door was shut, (even with the draft rod wide open). At this point it seems as though I will have to take a look inside the flue with a flue camera to see if there is a blockage at the offset or if the mason cheated and tapered down from the 8X12 to make the offset? Not sure, but something is going on. If that's the case, what the hell am I to do???

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Did you also try opening a window without the OAK to see if that helped?
How long are you letting it burn with the door cracked before shutting it?

Just thinking out loud, have a yard blower you could blow up the flue?
It would either change pitch drastically if the flue were clogged or blow whatever is clogging up the works out.

Have you checked the screen on the chimney cap? With all the cold weather, lots of people are finding their screens are plugged up. The moisture hits the screen, freezes and eventually can block the draft completely.