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Would this convection setup work?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by niagara, Jun 13, 2013.

  1. niagara

    niagara New Member

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    New member here, what a great site!

    Here's our situation: Existing house is an old 2 storey farmhouse 25'x30' footprint (1500 sq. ft. total). We're adding a large sunroom addition on the back 18'x30' with a cathedral ceiling.

    The stove we decided on is the PE Averlea T5.

    I'd like to install a grille at the top of the ceiling where it meets the original house and run a large insulated duct (maybe 10 or 12") through the attic and open up over the staircase.

    My theory is the heated air from the stove will rise to the ceiling, run through the duct, down the stairs, through the house and return back to the stove. Forming a huge convection loop, heating the entire house.

    I'm figuring this arrangement will drive itself, but would an inline fan/blower in the ductwork be helpful?

    Also, the house is well insulated but at 2000 sq. ft. total, should I buy the T6 instead?

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  2. mellow

    mellow Resident Stove Connoisseur

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    Most will recommend moving cold air rather than hot air, depending on building codes a return vent like that could not be that close to the stove.
  3. niagara

    niagara New Member

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    The vent isn't near the stove. The stove is on the outside (north) wall, the vent is on the south wall 18' away at the ceiling.

    There's no way to move the cold air. The air is simply making it's way back through the house replacing the volume that flows out through the ceiling duct.
  4. niagara

    niagara New Member

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    Here's a crude pic to show what I mean. aircirc.png
  5. Grisu

    Grisu Minister of Fire

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    The former owner of our house built something similar with the idea of blowing warm air from the heated living room through ducts in the attic into the bedrooms. In my experience the effect was essentially zero if not negative. The air coming out of the ducts was not noticeably warmer and could not keep the bedrooms at temperature when the doors were closed. When pulling out the system I also noticed that we probably lost quite a bit of warm air through the vents into the attic as the surrounding insulation was dark from dust. Closing the ceiling and putting insulation on top may save us more heat than the system did provide. Thus, I would try to not disturb your thermal envelope by going through the attic. How about putting a vent in the wall between the upstairs and the sunroom just below the ceiling instead of going up in the attic? An HVAC expert may be able to tell you whether such a system has a chance of working. Nevertheless, I would put the stove in the living room which seems to be close to the stairwell and let natural convection do the work. If you have a better sketch of your house we may be able to provide you with some additional ideas.
    Joful likes this.
  6. niagara

    niagara New Member

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    Thanks Grisu.

    Here's the original house. The foot of the staircase is at the front door on the right. Attached also are the plans for the new sunroom.

    Moving the stove is not an option, we'd like it in the new sunroom where we'll be spending most of our time.

    -Not too concerned with heat loss through the attic, there is already ductwork up there for the existing forced air system. Ducts can be made sufficiently airtight and can be insulated well. house-small.jpg floorplan-addition.png
  7. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Welcome to the forum Niagra and that is a beautiful old home you have.

    Usually those type of systems just won't work out well. Some have even tried to install fans to move but not too good of luck with that. You might be better advised to use a ceiling fan and have the air sucking up rather than blowing down. In addition you might try setting a real small fan near the top of the stairway and have that blowing down. But don't turn the fans on more than low speed else the draft won't feel good to you. Small desktop fans work well as they won't create a big draft. The reason for doing this is that trying to blow warm air into cool air just don't work well. However, if you move some of that cooler air towards the warmer air, that cool air will replace the warm air which means you actually will be forcing the warm air out of the stove room. Sounds backward but it works very well. (The cool air is more dense than the warm air and this is the key.)
    Huntindog1 likes this.
  8. niagara

    niagara New Member

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    Thanks Backwoods!
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  9. fossil

    fossil Accidental Moderator Staff Member

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    I really don't think your plan would make you happy...especially after all the effort & expense of installing it. Warm air convecting off your woodstove is really moving very lazily as compared to anything you think of from a forced-air furnace. It's not rushing up there looking for somewhere to go, it's not ducted, nor is it forced to move anywhere. If some of it happens to find its way up into your ceiling penetration, it's merely serendipitous...nothing is really encouraging it to go up into there. If it does, and happens to actually find its way over into the upstairs area, it's likely to have lost (or will rapidly lose) almost all of its sensible temperature above ambient in that space, and even if it's still a bit warm, it will just pool at the ceiling. I fear that you will never establish your desired natural circulation convection loop. But hey, I've been wrong before. ;lol Rick
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  10. Hogwildz

    Hogwildz Minister of Fire

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    Is there a hallway upstairs? And does it lead back to the wall that is next to the open cathedral area? If you can open up say a doorway size opening on the second floor at that wall next to the stove room, you may get a good convection loop going. I have a very high cathedral ceiling over my living room, with a ceiling fan hanging about 8 to 10 feet in the center of the living room, which runs in winter mode. I have a very large loft overlooking and open above two sides of the living room. I get a very good loop going where you can actually feel the heat coming down the stairs. Downside with any woodburner is, you get a draft at your feet where the cooler air flows into the living room as the warm air goes up and over. The duct is highly doubtful to do diddly.
    fossil likes this.
  11. begreen

    begreen Mooderator Staff Member

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    Post a picture of the total floor plan. Perhaps there is a better alternative.
  12. niagara

    niagara New Member

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    Thanks for the feedback. I'm away most of the day and can post a floorplan tonight.

    But no, the upstairs hallway doesn't carry through. The entire upstairs back is the master bedroom (the upper skinny window in the picture). I suppose we could put a window in the bdrm opening to the loft. That might allow sufficient air volume to flow through.
  13. begreen

    begreen Mooderator Staff Member

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    That might work well. Hot air will definitely accumulate up there, even with a ceiling fan which I would recommend.
  14. begreen

    begreen Mooderator Staff Member

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    Try the fan trick with a regular 12" table fan or box fan, running on low speed, on the kitchen floor pointed to the stove room. With a decent sized window from the upstairs hallway opening up to the ceiling peak of the new space you should get the desired convection loop.
  15. niagara

    niagara New Member

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    Sure, I'll try that. The HVAC guy said something similar. (He was here to assess the furnace capacity which is needed for the building permit.)

    He also suggested running a cold air return from the ceiling down to into the furnace so the fan could circulate the air around.
  16. begreen

    begreen Mooderator Staff Member

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    I would try it without the furnace fan first. It costs $$ to run the furnace fan continually and unless all the ductwork is insulated (returns included) the heat loss may negate the gains.
  17. Huntindog1

    Huntindog1 Minister of Fire

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    NEW WOOD STOVE LOCATION.png Thats a pretty large sun room with lots of windows. Plus the open ceiling plan.

    I am thinking its going to take alot more stove than you think to heat your house from that big open area with lots of big windows.

    Plus with having the stove away from the main house getting the heat to the other parts will be a struggle.

    Especially in the cold of the winter. And you living up North in Canada.

    I would go with the 3.0 cubic foot fire box of the T6 rather than the 1.97 cubic foot box of the T5.

    I would somehow install the stove in the middle where the house meets the new sun room.

    Some how have the stove sitting back into the old part of the house but facing the new sun room so you can sit in the sun room and enjoy the fire.

    This way the stove actually sitting back into the main part of the house you can open up a vent in the main part of the house close to the stove and in the ceiling to the upper floor.

    Placing the fan blowing down the stair well will let lots of warm air rise in your ceiling vent which is close to the heat source and a short path to up stairs.

    A 3.0 Cubic foot stove will still be able to heat your sun room from that location.
  18. TradEddie

    TradEddie Minister of Fire

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    I've had some (limited) success with the opposite of this, after trying in vain to draw warm air into the return, I closed the return in my stove room, and closed the supply registers in adjoining rooms. This increased the (cold) air being sent to the stove room and the registers in the other rooms drew air from the stove room. It didn't directly help upstairs, but drawing more warm air through the downstairs rooms allowed warmer air to the bottom of the stairs. You need to be sure you have adequate open return registers or you could damage the furnace fan.

    Floor fans blowing into the stove room work exceptionally well, but I don't like tripping over fans, and the Mrs. won't even consider it. I'm thinking of trying one of those tower fans next season which might be less intrusive.

    TE
  19. niagara

    niagara New Member

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    Folks, I'm updating this thread.

    Went with a whole new design. No woodstove, instead we're putting in a ZC fireplace in front of the stairs.

    It's an RSF Opel 3. Just installed it yesterday.

    fireplace.png
    Last edited by a moderator: Mar 21, 2014
  20. Grisu

    Grisu Minister of Fire

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    So in the plan you posted further up that would be on the right side, correct? I like that idea: during the day you have a nice, unobstructed view out the windows and at night you can fire up the fireplace and keep everything warm. I hope you will post more pictures once it is done.
  21. niagara

    niagara New Member

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    Updated floorplan...

    fireplace.png
  22. niagara

    niagara New Member

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    Precisely. The floorplan pic is upside-down but there are huge picture windows.

    View from backyard. It only shows half the rear wall but it's symmetrical. (Excuse the mess)

    fireplace.png
  23. begreen

    begreen Mooderator Staff Member

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    Congratulations. Will you be ducting heat off of the Opel to another part of the house? What is the large black hose? heading up near the chimney?
  24. niagara

    niagara New Member

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    Thanks!

    No, just the blower fan using the louvers in front at the top and bottom of the unit. No ducting.

    The black hose is the outside air kit connected to an intake on the roof. The black is insulation wrap to protect from condensation.

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