Questions about OAKs

[timbo]

I have a question for all you OAK guys. I have a P68 and am drawing air out of the room (no OAK at this time). My house is old so not very tight…stove seems to run OK. I think I would eventually like to hook it up to outside air but have several questions that I can’t seem to find the answers to.

1. Drawing air from the outside, especially when it is sub zero out, does the stove lose efficiency because it’s heating colder air, trying to bring it to set temps, or would drawing ambient air from, say, inside a room cause the stove to work “less” because rather than heating air up to 68 degrees from 20 below zero air it’s only heating slightly cooler air drawn from inside the room?

2. Can the OAK be made from PVC? I’m not sure how hot the inlet flange is when stove is running at full tilt, that’s why I’m asking. It would be easier for me to be able to use PVC vs 3” flex SS pipe if it’s OK to do.

Caution…answers may generate more questions

 

[krooser]

Most OAK kits you'll find are steel.... many codes require that. But I've also seen PVC... maybe use a corrogated metal flex pipe between the stove and the PVC....

The temp difference is negligible considering how hot the fire in the stove is. All high efficiency gas furnaces use out side air for combustion... no probelms there... and pellets burn hotter than NG.

 

[erikbrooks]

Agreed - the temp difference when cold out should not affect heat output too much. And I have 2 OAK installed, one on an Accentra insert which is using flexible metal "dryer" vent pipe, the other on a Harman XXV, which also uses the same vent pipe from the stove to the wall, where I then ran a few feet of 3" PVC.

 

[imacman]

Timbo, I have yet to hear a really good argument against an OAK, regardless of the "tightness" of the house.

Any way you look at it, without it, the stove is just one more device that pulls cold outside air into the home. So in effect, to burn the pellets, you are actually lowering the indoor temp, and then trying to heat it up again.

And with a house such as yours that is "leaky", the stove will just have an easier time pulling the cold air through the cracks.

As for the outside air going into the stove, colder air is denser, and contains more oxygen......more oxygen= better burn. Just ask any racer...they WANT cold air going into the engine so they can add more fuel and make the burn hotter.

I don't know about every stove manufacturer, but I do know that Englander and Harman recommend that an OAK be used w/ their stoves:

Harman:"Harman Home Heating and Hearth & Home Technologies strongly recommend attaching outside air in all installations, especially lower level and main floor locations."

Englander: "Outside combustion air is mandatory for these units to work properly"

As for the materials to make it, regardless of what ends up going through the wall, I'd start the piece that attaches to the stove as metal

 

[Xena]

The quickest way to get the right answer is
to look in your manual. If you don't have one,
they are available for the download in pdf format
from the Harman web site.

 

[timbo]

well, then, I guess an OAK is in order...Thanks all for the recommendations.

Macman, I am intimately aware of how cold air acts...having been in the aviation industry for a number of years before the job I'm in now, I know that take off lengths are much shorter in colder (denser) air due to more lift, you get a significant increase in horsepower in a recip engine / prop plane...everything you said makes sense. Thanks! And I never considered that pulling air from inside the house pulls outside air in through leaks (perform an "I should've had a V8" forehead slap). Not sure I can get it done this weekend but certainly with in the next couple of weeks I will do it.

Thanks all again! :coolsmile:

 

[timbo]

The quickest way to get the right answer is
to look in your manual. If you don't have one,
they are available for the download in pdf format
from the Harman web site.

Thanks

I do have a manual but although it mentions using outside air, it doesn't strongly recommend it as the quote Macman put in his post. I don't remember reading that at all in the manual and I have read that manual front to back literally a dozen times at least. I'll have to check again.

Tim


addendum...I just checked my manual (I have a pdf of it here at work) and it doesn't have the quote in it that Macman put in his quote...the only time it says that an OAK is not optional is in a mobile home and that "The benefit of outside air is mainly noticed in small, very tight, houses." I wonder if they have a newer manual now although mine is a brand new stove purchased this past May and the pdf I have is identical to the printed manual...anyway, regardless, I'm going to install an OAK jsut because of the benefits of doing so...

 

[hossthehermit]

I'm not saying OAK is a bad thing. Some installations, however, create their own situations. Mine is in roughly the middle of the cellar floor, vented into a center chimney, heats the whole house. tied into ductwork for FHA oil furnace. OAK would have to run about 15' horizontal across the floor, (talk about a tripping hazard). or 15' horizontal across the ceiling, then down 7' (talk about a walk into hazard). Either way, cold air coming in for that distance is going to create major condensation both inside and outside the pipe. Manual says it's not required, works for me.

 

[Havlat24]

I have an outside air intake on my stove. On my industrial dry kiln, I also have a makeup air unit. However it preheats the air before its used for combustion.

I've seen alot of pellet stove owners in northern canada scrap the outside air, because the things frost right up and drip water everywhere. Even while the stove is running, and if you think about -40C air traveling through into a stove is going to cause some condensation on the length inside the house.

 

[timbo]

Max length for my OAK would be about 3 feet. My stove sits on a hearth in front of a fieldstone fireplace...it would just have to go from the back of the stove over to the left side of where the fireplace meets the outside wall and then another 6 inches or so.

 

[timbo]

The other thought I had is right under where the stove sits is a crawl space (in fact the whole 15x22 foot room sits over a crawl space). I could just pull air in from there and it probably wouldn't be sub zero temps...

 

[imacman]

OAK is great when the stove is running but when its not the 2 air channels make a nice passage for cold air from outdoors through the stove which gets cold,absorbs heat & humidity. figure in the draft of a chimney & its a lovely cooler for the room as it condenses humidity within the stove. simpson i think makes an exhaust pipe which incorporates an OAK so to preheat the combustion air...maggie

Maggie, I'm curious....how often do you think the stove will be "off' from November - March, especially in N. Maine, or N.H.????

And all one has to do to eliminate the cooler air from entering in those rare moments when the stove isn't running, is to make sure that the outdoor air intake is a little lower than the air intake on the stove.....cold air doesn't go up.....walk into your basement in the middle of the summer.

Yes, there is pipe that incorporates the OAK.

 

[Havlat24]

OAK is great when the stove is running but when its not the 2 air channels make a nice passage for cold air from outdoors through the stove which gets cold,absorbs heat & humidity. figure in the draft of a chimney & its a lovely cooler for the room as it condenses humidity within the stove. simpson i think makes an exhaust pipe which incorporates an OAK so to preheat the combustion air...maggie

Maggie, I'm curious....how often do you think the stove will be "off' from November - March, especially in N. Maine, or N.H.????

And all one has to do to eliminate the cooler air from entering in those rare moments when the stove isn't running, is to make sure that the outdoor air intake is a little lower than the air intake on the stove.....cold air doesn't go up.....walk into your basement in the middle of the summer.

Yes, there is pipe that incorporates the OAK.

Us folks with basement installs are hooped though. Cold air is coming down!

 

[imacman]

addendum...I just checked my manual (I have a pdf of it here at work) and it doesn't have the quote in it that Macman put in his quote...the only time it says that an OAK is not optional is in a mobile home and that "The benefit of outside air is mainly noticed in small, very tight, houses." I wonder if they have a newer manual now although mine is a brand new stove purchased this past May and the pdf I have is identical to the printed manual...anyway, regardless, I'm going to install an OAK jsut because of the benefits of doing so...

From Harman's website, P68 owners manual, P.8:
"Outside Air:
Harman Home Heating and Hearth & Home Technologies strongly recommend attaching outside air in all installations, especially lower level and main floor locations.
The use of outside air is required for all horizontal venting configurations and for all installations in basement locations."

 

[timbo]

OAK is great when the stove is running but when its not the 2 air channels make a nice passage for cold air from outdoors through the stove which gets cold,absorbs heat & humidity. figure in the draft of a chimney & its a lovely cooler for the room as it condenses humidity within the stove. simpson i think makes an exhaust pipe which incorporates an OAK so to preheat the combustion air...maggie

Maggie, I'm curious....how often do you think the stove will be "off' from November - March, especially in N. Maine, or N.H.????

And all one has to do to eliminate the cooler air from entering in those rare moments when the stove isn't running, is to make sure that the outdoor air intake is a little lower than the air intake on the stove.....cold air doesn't go up.....walk into your basement in the middle of the summer.

Is it possible if the air in the flue is warmer than the OAK, then the rising warmer air would pull colder air into the system...as that cold air warms up in the stove/flue system (it is in a warmer house after all) it too would rise pulling more cold air in, creating this cold draft cycle that Maggie was referring to. Also, I have my stove on a setback t-stat so it does shut down during the night (at least for a while) and during the ay when we're not home....now when it gets a lot colder, as it certainly will, there may be less of the stove shutting down during these setback times...

 

[imacman]

..Us folks with basement installs are hooped though. Cold air is coming down!

Again, do think your stove is going to off for any extended period of time this winter in Northern Alberta?

 

[Havlat24]

..Us folks with basement installs are hooped though. Cold air is coming down!

Again, do think your stove is going to off for any extended period of time this winter in Northern Alberta?

Your point is taken.... We do experience the occasional Chinook, so I wouldn't say it would be out of the ordinary to have it down. Before your pellet stove did your furnace run continous?

 

[katwillny]

What does OAK stand for? what is it?

 

[jtakeman]

What does OAK stand for? what is it?

Outside Air Kit

 

[timbo]

addendum...I just checked my manual (I have a pdf of it here at work) and it doesn't have the quote in it that Macman put in his quote...the only time it says that an OAK is not optional is in a mobile home and that "The benefit of outside air is mainly noticed in small, very tight, houses." I wonder if they have a newer manual now although mine is a brand new stove purchased this past May and the pdf I have is identical to the printed manual...anyway, regardless, I'm going to install an OAK jsut because of the benefits of doing so...

From Harman's website, P68 owners manual, P.8:
"Outside Air:
Harman Home Heating and Hearth & Home Technologies strongly recommend attaching outside air in all installations, especially lower level and main floor locations.
The use of outside air is required for all horizontal venting configurations and for all installations in basement locations."

Very interesting Macman...you have a different manual than I have...page 8 on mine is all about exhaust venting, making sure everything is sealed etc. Outside air isn't mentioned until page 9 and there's no mention of outside air for lower level and main floor or basement locations. I ran a search on the complete document and it ain't there.

 

[imacman]

Is it possible if the air in the flue is warmer than the OAK, then the rising warmer air would pull colder air into the system...as that cold air warms up in the stove/flue system (it is in a warmer house after all) it too would rise pulling more cold air in, creating this cold draft cycle that Maggie was referring to.....

Yes, anything is "possible".

 

[katwillny]

Thanks jtakeman.

 

[imacman]

.....I ran a search on the complete document and it ain't there.

http://hearthnhome.com/downloads/installManuals/P68.pdf

 

[imacman]

..... Before your pellet stove did your furnace run continous?

No, but my oil burner doesn't have an OAK....I'm not sure I see your point.....

 

[Havlat24]

..... Before your pellet stove did your furnace run continous?

No, but my oil burner doesn't have an OAK....I'm not sure I see your point.....

My point is, it isnt that far fetched to assume that a pellet stove will not be running for periods of time in the winter. Especially the thermostat controlled ones. We all know the inherit variables associated with winter.