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Are there any OAK designs that shut when there's no fire?

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by whit, Nov 20, 2011.

  1. whit

    whit Member

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    With the many OAK fans here, the argument for having outside air piped to the stove while the fire's going are persuasive. Yet the fire's not always going, so from both condensation concerns and avoiding bringing in cold air when it's not needed concerns, it would be nice to have an OAK with a hatch of some sort that shut firmly when there's no flame to feed. Are there any on the market, or any designs that can be easily built at home?

    A spring-loaded hatch relying on suction to open it probably wouldn't be a good enough design. If the spring is light enough to open with the moderate suction of a pellet stove, then it wouldn't shut the hatch that firmly, and a breeze from outside could open it. Something that combined suction with electromagnets to hold it open or closed might be sufficient. Or something that was purely mechanical with a small motor and the right sort of linkage into the stove's logic. Okay, I don't have a clear, good idea. Except I'm sure such a thing could be designed, and would expect the parts not to cost all that much. Since there's some real electrical and mechanical engineering talent here, assuming there's not already an automated OAK hatch on the market, what would you suggest?

    I get it that if the stove is running constantly all winter, and the OAK disconnected in summer, there's little need for such a thing. This is more for those of us who often have stoves only cycling on for brief periods in shoulder seasons, or which are mostly off during sleeping hours because we prefer a chill room and blankets for sound sleep, or whose stoves are off for a week at a time mid-winter while we're off to grandmother's house - it would be convenient, energy saving, and perhaps prevent corrosion of the stove to have the OAK shut itself when the stove has no call for outside air just then.

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  2. jtakeman

    jtakeman Minister of Fire

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    Some stoves have a flapper in the intake. My Omega does anyway. On a windy day with the stove off is often annoying to listen too! But mine is in the basement so I hear nothing up stairs. If it was right in the livin room? I'd be ripping that thing out! Careful what you wish for.
  3. rona

    rona Feeling the Heat

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    A Harman PC45 has a flipper built in that will do what you ask.
    A old time plumber would install a fresh air pipe from outside down close to the furnace and drop it into a pail. he claimed the cold air stayed in the pail unless the furnace ran then it would be sucked out of the pail and drawn into the furnace. This was done to lessen drafts in the house. I thought that was pretty good as people way back knew the problem and yet there are still people that dispute the need for fresh air intake today.
    Just for fun I tried his idea since I had a basement install. First I left a open pipe beside the stove and you could feel the cold air spread out on the floor. Next I set a pail down and put the pipe in the pail. No cold air came out as cold air settles. But if the stove came on then the cold air came out of the pail but was sucked into the stove.
    I guess the simple way of proving this is if you have a air conditioner on the main floor of your home and try to cool off the second story with the bedrooms using fans. It just doesn't work as cold air settles and hot air rises.
  4. whit

    whit Member

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    Yeah. Something the wind can open wouldn't be good. With the stove off, I'd like to have something that just stayed positively closed, preferably flush with the house wall, with a tight seal. Triggering it by the thermostat would be one way. As long as the thermostat calls for heat, it would be open. When the thermostat stops, it should lag by a couple of minutes as the fire goes out, then close - and stay closed until the thermostat calls again. The world's full of little servo motors that can do that sort of thing, for instance in fancy cars where steering wheels, seats and so on adjust when you turn the key. This would be a very simple flap that would adjust when the thermostat turns the key, and lags when the thermostat turns off - just as those fancy cars will have inside lights that lag as you exit the car.

    Granted, when cars start acting like that I find it a bit annoying. My point is just that the world's awash in this sort of thing, and the electronic parts to assemble it readily available to a person who knows how to spec them from which suppliers. Which certainly ain't me.
  5. flynfrfun

    flynfrfun Minister of Fire

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    To truly accomplish what you are wanting, you would need the same mechanism on the exhaust piping too. Since both the OAK and the exhaust can bring cold air from outside into the stove.

    But, really why worry about cold air coming into the stove? With a correctly set up stove, it is sealed within the stove and doesn't come out into your home anyways. The stove itself will get cold, but the cold air should not infiltrate your living space since the path from the OAK goes into the stove and then back out thru the exhaust.

    Edit: This applies to my Enviro M55. I know some stoves don't have a sealed OAK connection to the firebox...so yes those would allow cold air to come into the home.
  6. whit

    whit Member

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    Ah, but the exhaust takes a long and convoluted route, that goes through a very small port behind the stove baffles. An OAK, by design, is a short strait shot in. In my case, it would be on a north wall which often takes a strong cold north wind in the worst of winter. My exhaust goes out the other way on the corner, to the west, where the wind blows past rather than into it.

    For one thing, I don't want condensation within the stove. If the stove gets cold, that'll create some, given a house with a good enough envelope to be on the humid end of what's advised for winter. I've seen people in other discussions here advising disconnecting OAKs over the summer to avoid trouble. Nobody seems to advise taking your exhaust system out for the season. Is that just relative convenience? Or are OAKs more prone to lead to trouble?

    The generation of Quad Santa Fe I've got heads it toward the firebox, but I wouldn't call the connection "sealed." People say the latest model is better in that regard.

    Probably I should ask my nephew who's on his high school robotics team what it would take to have a small servo open and close a door in response to the thermostat. I wonder what catalogs they get their parts from?
  7. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    Both sides of the venting system need to be sealed off during the summer or you have to be certain to get all interior metal surfaces coated with a light oil.
  8. flynfrfun

    flynfrfun Minister of Fire

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    Ah...OK. You have a Santa Fe. I believe it doesn't have a very good OAK design in that it just sucks the air out from around the bottom of the stove instead of having an actual 2 or 3" pipe to connect to. However, I have seen some guys on this forum create a sealed system by building a sheet metal adapter and then piping it outside.

    Since your OAK faces the wind, probably the best thing I can think of would be to make sure you have a 90 on the outside piping so the wind can't blow directly into it.

    I'm sure it is possible to do what you want, but it's going to take some knowledge and skills to do it, plus will add some complication to the stove. Sorry, I can't help much with your design, other than servo's are cheap and easy to get at your local hobby shop. It's just getting them interfaced to work with your stove is not going to be easy.
  9. whit

    whit Member

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    The other way of looking at this is: If it's a good thing to do, and also makes sense for the exhaust in terms of blocking negative effects, on balance it would only be good for the OAK. If you have a cap on the exhaust and it fails and stays closed while the fire's going, you're in a world of trouble. If the OAK cap fails and stays closed, the stove still operates fine. With the exhaust, you can't afford for it to fail, so it would have to be ridiculously and expensively over-engineered. For the OAK, it could be a cheap little thing, because failure just wouldn't cost you much.
  10. whit

    whit Member

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    Oops. I've been getting away with something. Haven't noticed any ill effects. But would be easy to stuff a rag into the exhaust port after the last firing. I'll be sure to do that. Thanks.
  11. flynfrfun

    flynfrfun Minister of Fire

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    After re-reading your original post, you didn't say that the flap has to be automatic. So, maybe you could build a flap into your OAK and use a pushrod to manually open/close it each time you want to. The pushrod would be operated from inside the house. That wouldn't be very hard to make and you might even find what you need at the hardware store mostly ready to go.

    If you want it to automatically open when the stove comes on...that's out of my expertise. Can't help with that. But sounds like you would need to wire the thermostat to a relay of some sort that could power the servo with the correct voltage from the stove. But when the stove shuts down, you'd have to have a timer of some sort so that it doesn't close until after the stove actually shuts down. This happens a good 20-30mins after the thermostat has stopped calling for heat.

    I still think you're going to get humidity into the stove unless you seal both the exhaust and the OAK. It doesn't matter that the exhaust has to take a lot of turns. Air carries humidity and if it can get out of the stove thru the exhaust, it can get into the stove the same way...just take longer. Even though the closed OAK would stop the air from flowing freely, the humidity would still slowly work it's way thru the exhaust into the stove.

    My opinion...keeping humidity sealed out of the stove is going to be a real pain (at least in the way you want to). But, you could save a lot of cold air from coming into the house by sealing your stove to an OAK, so that the cold air can't come into the house....that's where your biggest benefit would be. Just my .02.

    If you do build the automatic system, I'd love to see pics...
  12. gerryger

    gerryger Member

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    The older models of the Santa Fe had that poor OAK design you are talking about, however on the newer models the OAK does get connected into the combustion chamber.

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