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Outside air kit details, the often forgotten screened inlet

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Highbeam, Oct 27, 2008.

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  1. Highbeam

    Highbeam Minister of Fire

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    On my Hearthstone stove (and maybe your stove)the details for the outside air connection include instructions to screen the inlet with 1/4" mesh to keep out farm animals among other things. I had never done it but I am having insulation installed soon and I did want to rigidy mount the inlet to something instead of just dangling down there in the crawlspace. It is important that the inlet be below the insulation level to keep things flowing. The crawlspace is vented on all sides to atmosphere.

    The outside air kit has always been good for me. It constantly flows cool air into the OAK, through the stove, and up the chimney all year long.

    To clamp the end of the semi-rigid aluminum duct to the beam in the photo would have been difficult to do without smashing it so I knew I needed to use a fitting and then I figured I could hose clamp the steel mesh to the fitting as well. Well, I didn't want the mesh to be a restriction so I used the tee to double the screened inlet area.

    Note the remnants of the original masonry chimney in my crawlspace. I added significant structure to help support the stove and hearth.

    Do you folks think that my little screen system is proper? I am not concerned with fire working its way down the tube.

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  2. Ithaca

    Ithaca New Member

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    Looks good to me Highbeam. But what do I know? Your mesh serves the function well enough I'd say.

    I am curious what you used to fill the excess space around the 3" flex that goes into the tile?

    Nice setup overall.

    I have an OAK also and have been very happy with it.
  3. Highbeam

    Highbeam Minister of Fire

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    Thanks Cook, the gap between the aluminum pipe and the tile/durock and then again where the pipe passes through the subfloor were abundantly filled with fireblock or firestop caulking sold at HD. It wasn't real cheap but I didn't want to use grout since the cement might react with the aluminum. The caulk is grey and gets whiter with exposure. It matches the grey grout of my tile real well and was easy to put down.
  4. Ithaca

    Ithaca New Member

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    The caulk looks good. I didn't know they made it.

    I mucked mine up with stove cement to seal the air gaps. It is in the old fireplace floor so no one sees it, but now I know how it should look!
  5. Ivy Frank

    Ivy Frank New Member

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    When in doubt, paint the pipe flat stove black. Much less noticeable. I have a 4" standard duct pipe coming straight up under my unit, so you can see it from ground level and from the back of the stove. I plan to enshroud it in a tin surround, painted flat black to match the stove.
  6. semipro

    semipro Minister of Fire

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    Nice job on the OAK. Despite naysayers I strongly believe they're necessary in a tight house.

    Your setup reminds me somewhat of what I did in a rental house heated by a wood stove. Being that it wasn't my house I didn't want to make permanent alterations so I removed one of the 4x4 ceramic tiles on the hearth area behind the stove and drilled a 3" hole in the subfloor to the crawlspace below. We'd remove the tile while the stove was in operation and replace it when not burning. I re-installed the tile when we moved out.
  7. savageactor7

    savageactor7 Minister of Fire

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    That will last forever and a day Highbeam...it's neat too.
  8. Johnnaris

    Johnnaris New Member

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  9. karri0n

    karri0n New Member

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    Apparently so will this thread!

    Someone bumps this thing once every couple months. Your OAK project has immortalized you, HB :)
  10. Highbeam

    Highbeam Minister of Fire

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    It might last forever since I have it stuck in my signature for reference. I also try to use common key words in the thread title so that it comes up easy in people's searches since I know that I've dug up some old threads when looking for an answer.
  11. dreezon

    dreezon New Member

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    Would that mine could be anywhere near so simple. I have about 20 feet to travel and a minimum of 4 bends. Would also have to modify a window or cut a hole through the side of my basement wall to the outside.
  12. burkeb

    burkeb New Member

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  13. sugarloafer

    sugarloafer New Member

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    Highbeam,

    That looks pro. Very neatly done. Thanks for sharing the pics.
    I am curious, does the Hearthstone OAK feed both the primary and secondary air inlets? I like the idea of a.) plugging any holes to the outside and b.) eliminating any negative air pressure in the house that would pull cold air in through gaps and cracks. I just finished a Homestead hearth install and am contemplating running an OAK down through the old ash dump and outside.

    Thanks
  14. LLigetfa

    LLigetfa Minister of Fire

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    An easier way to mount the screens is to cut a disk of screen a little larger than the ID of the opening, dome the middle in enough to reduce the diameter, and shove it in dome side inward. It will hold amazingly well.
  15. cyclone

    cyclone Member

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    Why would you be concerned if fire will go down the fresh air hose.?
  16. Highbeam

    Highbeam Minister of Fire

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    On the heritage for sure, all air comes in through the oak nipple. Primary and secondary so there are no other intake holes on the stove and all intake air comes in from outside. I have heard of some other brands of stove that have seperate primary and secondary inlets with the secondary fed from some unsealable source. Boo! In theory, I could plug up my OAK tube and it would shut off all air to the fire.
  17. Highbeam

    Highbeam Minister of Fire

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    I'm not concerned with fire going down the air tube. More concerned with insects or rodents. The specs called for the screening, I don't think it hurts so I put it on there. It was probably easier to cut it big and hose clamp it than to try and precisely cut the mesh to fit. It's not like I have a mesh shortage.

    It's the law to have these OAKs in WA and in many other places. I agree that it's a good idea as well.
  18. Todd

    Todd Minister of Fire

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    My old Homestead had a seperate secondary air inlet in the back of the stove. The primary was on the bottom left near the air control.
  19. Highbeam

    Highbeam Minister of Fire

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    I almost would rather have a secondary air inlet somewhere else so that I could close it off partially to slow down the rip roaring secondary burn when things start getting too hot.
  20. VCBurner

    VCBurner Minister of Fire

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    Nice job, great pics. I was thinking of intalling one on the basement stove. The stove is kiddy cornered, I would run the pipe up the corner and cut out a whole to the outside in the rim joist. Is there a problem runnig the pipe up instead of getting the air from a lower source? Thanks for the cool pics and usefull info!
  21. Highbeam

    Highbeam Minister of Fire

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    The only problem I can see with an OAK in the basement, I've never actually had one in a basement, is that the cold air will want to pour into the stove all the time. If your secondary air inlets are open to the room then perhaps this pouring air might blow out through the secondary inlets rather than up the chimney. That's a long shot but I suppose it's possible.

    The install manuals do not require the slope of the OAK intake pipe to be up or down. Some installs are even horizontal. Since so many jurisdictions require an OAK system and since there are basement stoves everywhere, I can see no reason that it won't work just fine.
  22. VCBurner

    VCBurner Minister of Fire

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    "Thank you for the info. I think I'llm try it. I hate feeding the stove heated air. Burn on."
  23. Todd

    Todd Minister of Fire

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    Lots of OAK questions lately. I had a vertical OAK run for my basement install and could not control the cold air pushing into the stove even with a damper and U in the pipe. It cooled off my stove prematurely and also think it created shorter cooler burns. I took it off and stove burns much better.
  24. VCBurner

    VCBurner Minister of Fire

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    "I definetelly don't want shorter/cooler burns. Maybe I'm better off leaving it alone. It burns fine as it is and gets some of its supply from upstairs replacing the cooler air with warm air. I guess that helps circulate the ait through the house. Why mess with it if it works fine, right? Just wondering, what do you think the difference is between air intake on a first floor OAK instal and a basement one? Thanks for the input Todd!"
  25. LLigetfa

    LLigetfa Minister of Fire

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    At some point between the basement floor and the upstairs ceiling, there will be a neutral pressure plane. More pressure above the NPP and a deficit below it. Where the stove sits in relation to the NPP will affect the burn but more importantly, could affect the propensity for it to let smoke into the room.

    It is always best to lower the NPP by controlling leaks in the building envelope. An OAK fed stove below the NPP could have more problems with smoke than a room fed stove.

    I'm not familiar with Todd's stove but I am surprised that the OAK had such a negative effect. If a stove is not running in the sweet spot WRT internal temps, I could see where the cold air could push it further from the sweet spot as the combustion air needs more preheating. I think though that the stove might already be running under marginal conditions that necessitated more air than it should have.

    With my OAK fed stove, if I open the air too far, I actually get less heat from it which is a bit counterintuitive. I find the OAK does turbocharge the air so it will raise the minimum burn to the point I could not shut it down far enough but I compensated for it by reducing the zipper air. I don't regret having an OAK and would not want to be without it. I don't want to send humid room air up the flue that then needs to be replaced by drafty cold dry air sucked through cracks in the building envelope.
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