why can't i use pvc for my OAK?

jeffd3889 said:

I used the OAK kit that came with my stove. Installation was simple... I just dont like the looks of the tubing - kind of cheap looking.

I have heard I should not use PVC, does anyone know why? What else could be used? any pics?

Thanks!

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You might want to ponder what happens if the exhaust manages to go out through the air intake.

That is the reason that an OAK must be made of metal.

IF you have a fire, heaven forbid, and the insurance company sees that you didn't follow the installation procedures, you are screwed. That's #1.

I confess I wondered the same thing and there are those on here who use it, however I think it may have to do with another problem. Suppose you are burning happily along and the power goes out. Your burn pot is almost red hot and sticking down into the intake area. Now heat convection takes over and, if you are lucky, the heat goes up the exhaust and pulls fresh air into the OAK to keep it cool. If there isn't convection or enough of it, your OAK is subjected to the heat of the burn pot and floor of the fire area. In the worst case, convection goes the other way because of wind outside or some other cause and the heat goes into the PVC pipe...... You're screwed again. That's just my guess but it made enough sense that I'm using metal pipe for mine.

Smokey, you and I must have been typing at the same time. You're just faster than I am.

I do not have an oak on my pf100 and at startup there was a lot of smoke filling the furnace before it lit and when it did there was a rush of air that came out the oak inlet and I am sure there could be hot embers in that airstream and if they were to land in pvc pipe it could start a fire so metal is the only safe way to go!

jeffd3889 said:

Makes enough sense for me! Thanks for the advice guys.
I guess it does not look so bad afterall

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ha ha ha. Love your answer. Also it makes sense about the whooosh at start up.

If you don't like the looks, you have options. One, there is an exhaust that has the OAK built surrounding it so you only have one pipe going out. Two. if it is the looks of the flex pipe, take in off and go to a muffler shop. They'll make you a solid one you can paint with heat resistant flat black. Ck your stove manual. you should be able to find a statement that will tell you that the entire OAK has to be metal. If something bad happened, how would you ever explain that you neglected to follow instructions?
Glad you opted to do it right. I tried the PVC short cut for about a day. Our friends here turned my head back around so I could see the flaws in my reasoning and I thank them again and again. There is enough trouble that finds me without my going looking for it.

my Harman invincible instructions say specifically to use PVC
so I would guess it was tested safe
I know the invincible is older but I would say it had to be UL approved
to be in the directions

On both my installs I used short pieces of PVC on the thru-wall connection. I used a hole saw that was slightly bigger than the PVC OD, I tapped the PVC thru the wall and had a nice tight seal. From the stove to the PVC I used aluminum flex or automotive heat riser pipe .

ironpony said:

my Harman invincible instructions say specifically to use PVC
so I would guess it was tested safe
I know the invincible is older but I would say it had to be UL approved
to be in the directions

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I've seen some installation instructions that say that, perhaps those stoves don't have a closed OAK system, meaning they have a set of slots or other penetrations in the air intake path that would be used as exhaust exits instead of anything actually going out the OAK.

dac122 said:

On both my installs I used short pieces of PVC on the thru-wall connection. I used a hole saw that was slightly bigger than the PVC OD, I tapped the PVC thru the wall and had a nice tight seal. From the stove to the PVC I used aluminum flex or automotive heat riser pipe .

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On that England Stove Works Stove you have a non code compliant installation.

SmokeyTheBear said:

ironpony said:

my Harman invincible instructions say specifically to use PVC
so I would guess it was tested safe
I know the invincible is older but I would say it had to be UL approved
to be in the directions

Click to expand...

I've seen some installation instructions that say that, perhaps those stoves don't have a closed OAK system, meaning they have a set of slots or other penetrations in the air intake path that would be used as exhaust exits instead of anything actually going out the OAK.

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you are correct in that assumtion
that is why I never hooked one up
would still draw room air so I seen no benefit

Anybody seen smoke going out there OAK when they loose power?

mcmaxx...
When my PF100 unit was new, got the dance routine a few times, thought the furnace was going to walk out
of the utility room. Believed it was due to too many pellets trying to get started, and an excess
amount of smoke. Thought it exploded a few times, so noisey.
Changed my setting to let a smaller amount of pellets into the burn pot when starting up. That is
one reason that I am on manual vs automatic start.

I've tested my Fahrenheit by pulling the plug while it's running, flame basically goes limp and the fire dies out fairly quickly, exhaust went out the PL vent exactly as it should have. In situations where the OAK/exhaust are installed properly, and the stove/furnace was engineered intelligently, a reverse flow of exhaust/fresh air should not occur. However, in the unlikely event that it does, you'd be potentially SOL using a PVC OAK duct. PVC is not designed to handle corrosive and hot flue gasses, the pipe could melt, releasing toxic fumes and CO into the living space.

#1 *should* always be safety of those living in the home, not whether or not the insurance company will reimburse you if property damage or personal injury occurs (this demonstrates how insurance companies really own all of us in the US, people are more concerned with the insurance companies' way of thinking before they're concerned about their own families).

j-takeman said:

Anybody seen smoke going out there OAK when they loose power?

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Good question J-takeman.

Geez, I always seem to run against the rules of convention here. I've used a PVC OAK for 5 years and have had at least one loss-of-electric shutdown, no problems, at least that time. I'm gettin' paranoid after reading this discussion. Anyone ever had a meltdown of their PVC OAK??

In an installation were the OAK is higher than the stoves air wash. There is a good chance it could become an exhaust outlet! My basement install has such an issue and the reason my OAK is ALL metal! Yes it gets hot! And hot enough to melt plastic, My first vent was not all metal. The cage was plastic and it did deform! The cage I have now is aluminium!

There was one person on here a year or so ago that managed to operate a biomass furnace for close to a year using large diameter PVC, over time its performance got worse and worse. The PVC was melting and collapsing.

I'm trying to tread lightly here, what I really want to say Craig and his moderators would likely have a fit about, this is fire and all of its byproducts that are in play here.

Not exactly something for experimenting with.

I love to poke at things to find out what makes them tick as much as the next tinkerer does, but I draw the line when it comes to things that can cause major problems if I screw up.

The most simple reason that us manufacturers are required to tell consumers to only use metal pipe for outside air connections is because that it was ASTM E 1509 dictates. We have no choice but to require what the test standards require.

despalmy said:

j-takeman said:

Anybody seen smoke going out there OAK when they loose power?

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Good question J-takeman.

Geez, I always seem to run against the rules of convention here. I've used a PVC OAK for 5 years and have had at least one loss-of-electric shutdown, no problems, at least that time. I'm gettin' paranoid after reading this discussion. Anyone ever had a meltdown of their PVC OAK??

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Go to this link, One of the moderators posted a picture of a failed PVC OAK https://www.hearth.com/econtent/index.php/forums/viewthread/63203/

save$ said:

Go to this link, One of the moderators posted a picture of a failed PVC OAK https://www.hearth.com/econtent/index.php/forums/viewthread/63203/

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That thread is pretty hilarious, people started talking about venting their "pallet" stoves with oodle noodles and the cardboard cylinders inside toilet paper rolls. I think someone needed to add that in order to vent with the cardboard inside a TP roll, you need to stick them into the cardboard inside a roll of paper towels to get the double-walled benefits.

Does anyone see anything usafe about using aluminum flex dryer vent, rigid aluminum dryer duct, or 3" galvenized metal duct for an OAK? I was looking at that flex automotive exhaust pipe as well.

One way to know if those metal materials aren't capable of causing a problem might be to touch the intake pipe while the stove is well heated. That will tell you how hot it is (though one of those newish infra-red thermometers would be less risky to your finger) It's probably just warm. But those materials are 3", and the pipe is what? 2"? You could use a reducer but it's preferrable to make a 2" hole in a wall than a 3" hole.
The kind of pipe used to make swing sets and chain-link fence posts is about the same diameter, and is probably available at hardware stores.

My pf100 OAK is actually cold most of the time,frosty right at the point it enters the house. I used the 3"dryer galv. duct and the flex aluminum at the furnace itself. I'd rather use something not so flimsy-cheapo. Maybe the automotive flex.
My OAK inlet is 2-3/4" so 3" isn't so bad.