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Air Circulation Question

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Max Headroom, Jul 13, 2008.

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  1. Max Headroom

    Max Headroom Member

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    OK, here goes. I've been lurking here for a while and have gotten some great info. My insert (Lopi Declaration) is being installed in about a week, and I've been noodling on the best way to circulate the warm air. The unit will be in my family room, adjacent to the kitchen with a six foot opening in between. I figure it'll be pretty easy to keep those two rooms toasty. Beyond that anything else will take some effort. I have a central AC system, separate from my heating system with the heat exchanger in the attic. Intake ducts are upstairs (top of the stairs and a couple of bedrooms). Would it make sense to open up one of the intakes and the outlets downstairs in the family room by the stove, and run the fan periodically, bringing cooler air to be warmed, and pulling some warm air up the stairs? I know I'll lose *some* heat circulating through the cold space, and running the fan isn't free, but the system is meant to circulate air throughout the house. Seems to me that it should work. Any thoughts?

    Thanks!

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  2. burntime

    burntime New Member

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    If you burn 24/7 the home will create some of its own "circulation" to balance. The general rule is to blow the cold air towards the warm to help distribute. I also run the fan on my furnace. Some say it is bad, others agree with me. I think it has more to do with the dynamics of your house than anything else. Try it!
  3. fossil

    fossil Accidental Moderator Staff Member

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    Attics above and crawl spaces beneath are typically insulated from the living space, but are vented to the environment, so they get real cold in the wintertime. Air distribution ducting is typically insulated, but only to about R-8 or so. The air doesn't move particularly quickly through those ducts, so it has plenty of time to lose whatever heat it's carrying in the winter as it passes through those spaces on its way back into the living space. Where do your ducts run? It might do some good, it might not...depends on how your house is put together. A blower on the insert and a ceiling fan in the room where the insert resides is a start on diffusion/mixing of that warm air your woodburner (space heater!) is producing. Distributing it from there effectively is a challenge we all face. Lots of things to try. Rick
  4. Max Headroom

    Max Headroom Member

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    Thanks for the responses. I was concerned that I was missing something fundamental. But seeing that I haven't gotten any "boy are you an idiot" responses (at least not yet) I'll go ahead and try it out once the season is here.
  5. fossil

    fossil Accidental Moderator Staff Member

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    Absolutely, try it out, it may well work for you. We tried running our fan (forced air electric furnace) for the same purpose, but all our return air ducting runs through the crawl space, so what we found was the heat was all pretty much lost on the way back into the house, so all we got from the supply registers was cool air we had to heat up all over again. I've recently had installed, as part of a major remodel, a completely separate little system...an inline fan (from FanTech) with a filter, that will take a suction from any of three floor registers in the most remote corners of the hardest to heat rooms, and return that air through a floor register in the hearth immediately behind the woodstove. My hope is that I'll pull cold air from those rooms, deliver it back to the heat source, and the air will be replaced in those rooms by warmer air entering through the doorways. I'll find out next season whether or not I'm an idiot, I guess. :p Rick
  6. begreen

    begreen Mooderator Staff Member

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    It's worth a shot, but often the duct losses counter the heat gain. It really helps to have an accurate portable thermometer so that you can objectively monitor the air temp coming from the registers and in the room. I like the inexpensive Radio Shack digital unit. If you see a 5-10 degree rise over an hour, then it is working really well. If there is only a 2 degree rise, then probably not. However, often a fan placed low in the colder area pointing towards the stove area can achieve significant gains and is also worth a try. A box or desk fan running at low speed usually works well.

    Code note, the return air grille is not supposed to be closer than 10 ft to the stove.
  7. tkirk22

    tkirk22 New Member

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    Give it a try. It may work...It may not work. We have baseboard electric, AC, and an insert in my house. All the ducts run below the house in unconditioned space. I turn the circulation fan on when the stove is running. You can't feel any real heat coming out of the vents but it does work for us. I haven't used the baseboard electric in our bedroom since we had the stove and that room is the farthest from the stove with a closed door.
  8. fossil

    fossil Accidental Moderator Staff Member

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    Well, hmm. I'm a big believer in code. I wonder what the thinking behind this is? This stove was professionally installed, permitted & inspected, and the inspector and I stood right there talking about what that register was for, and he just said OK, signed off the final, and that was that. Don't want to hijack the thread...BG, maybe you could PM me your thoughts, or a reference...I want to be safe, above all. Thanks, Rick
  9. Max Headroom

    Max Headroom Member

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    The good news in this case is that I'll be moving the already cooler air upstairs through the cold space to the downstairs room, so I won't feel like I'm sacrificing precious BTUs to the cold ducts. I'll definitely give it a shot, but for now I guess I should focus on getting the insert installed. I don't think I've ever been this focused on cold weather at this time of years. Maybe I'll put up the Christmas lights next weekend!
  10. SlyFerret

    SlyFerret Minister of Fire

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    If your system is moving cooler denser air into a warmer area, it will displace the lighter warmer air throughout your house. Your particular setup might work just fine! Like some of the other guys have said... every house is different in the way air circulates around. You've got nothing to loose, so give it a shot!

    -SF
  11. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    I think he is referring to the negative pressure return air vent Rick. The one that would suck smoke, fire and pestilence into it and distribute it via the ductwork in case of a fire in close proximity to the stove.
  12. fossil

    fossil Accidental Moderator Staff Member

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    Yeah, BB...terminology. In HVAC terms, what I have in the hearth behind the stove is a "supply" vent, not a "return" vent. The inline fan is variable speed, but not reversible...there's no way it could take a suction from behind the stove and deliver to another area of the home. Rick
  13. Max Headroom

    Max Headroom Member

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    Yes, as SlyFerret described I'll be moving the cooler air from the upstairs into the ducts (supply?), through the system, and return it to the downstairs room with the stove (return?). I'm not exactly sure of the correct HVAC lingo. The other returns will be closed so the cooler air will only go to the room with the stove. be No risk of smoking up the house. The only risks I see are wasting $$ on electricity to run the on the fan, losing heat in the cold attic space, and not having the warm air circulate as desired. Thanks again for all of the feedback.
  14. fossil

    fossil Accidental Moderator Staff Member

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    If, when the fan's running, air's being blown out of the register into the room, it's a "supply". If air's being sucked into the register out of the room, it's a "return". Supply from the system to the living space, return from the living space to the system. If in doubt (air flow can be pretty subtle in some cases), turn on the fan and lay a piece of paper or a plastic bag over the register... a return will suck it down onto the register, a supply will blow it away from the register. Rick
  15. Cluttermagnet

    Cluttermagnet Minister of Fire

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    I've heard conflicting advice in here- as to whether you should try to move warm air around (with fans mounted high) or blow cool air towards the wood stove. Which is it? Or should I try both (not at the same time)?

    BTW no 'central air' in my house, only a central heating system (hydronic). I plan to move some portable fans around and experiment. And only one ceiling mounted fan in an adjoining room to the living room where the wood stove is. I'll try that one, too.
  16. Max Headroom

    Max Headroom Member

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    Thanks for the clarification Rick. I had the terms backwards. So, my "returns" are upstairs, and my "supply" is downstairs by the stove.
  17. Jags

    Jags Moderate Moderator Staff Member

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    Clutter, several years ago I ran a very scientific experiment with my stove and moving air (the science part was moving the fan around). By far, pushing cold air TOO the heat source was the more efficient way to level out the heating.

    The common theme that I see popping up is: If you try to push warm air from the stove to other areas, you are really stirring up the air. It may sound like a good idea, but the most effective way to move air is with a "current" or convection. For that, moving cold air along the floor (where it lays naturally), is easier than trying to mix everything up.

    I have one small bedroom off of the living room, not matter how much I tried to "push" warm air into that room, it never worked, even when using a large box fan (scientific testing phase) directly in the doorway. I use a small clip on desk fan at floor level, and "pushed" the cold air OUT of the room and bingo, the room heated up even using a MUCH smaller fan.

    Jags scientific conclusion: move the cold air along its natural path TOO the stove. The cold air that is being moved away will be replaced by warmer air ( tadaaa....current!).

    Try it for yourself.
  18. fossil

    fossil Accidental Moderator Staff Member

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    The usefulness of ceiling fans that are so often mentioned in this context lies in "unstratifying" the air within the room where the space heater's located. The importance (and effectiveness) of this is directly proportional to ceiling height. In a room with vaulted, or cathedral, ceilings, it's basically essential to the overall efficiency of the room/heater system. Even in my little workshop with 10' ceilings, my small ceiling fan makes a world of difference. Gently mixing the air allows me to burn less fuel, because I'm really taking advantage of the heat being produced by the stove to increase the comfort of the space down where I am instead of up within a couple of feet of the ceiling. But, a ceiling fan does basically nothing to move air horizontally out of the room where it's installed. To do that, you need some other fan(s), and, as others have said, the most effective way to do it is to move the cold air low in the space toward the heat source, and let the warm air find its way back to replace the air you're moving. Rick
  19. burntime

    burntime New Member

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    I disagree Rick, I have an open concept and the ceiling fan does a great job of moving the air, obviously not as well as a box fan but I think it does very well. I think every home is different and experimentation is the key.
  20. Jags

    Jags Moderate Moderator Staff Member

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    Rick, you have a very valid point in the destratification of a room. I was not taking into consideration the room where the heat source was actually located.

    Burntime- as you mentioned, you can get some residual movement with a ceiling fan, but this is limited to "open" homes like you stated. Basically it is like you are heating one big room.

    But, if you are trying to heat a room (such as a bedroom), nothing beats a fan at floor level moving the cold air out in my opinion (and scientific experiments %-P ).
  21. fossil

    fossil Accidental Moderator Staff Member

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    Yeah, burntime..."open" being the operative word here. The more open the floorplan, the more opportunity there will be for mixing/diffusion in three dimensions. Adjoining my shop is another space, through a 48" x 84" wide open walk-through doorway (no door). When my shop is warm & toasty, ceiling fan on updraft medium speed, that space immediately on the other side of the opening sees very little benefit from the stove. You can feel the warmth immediately and dramatically when you pass through there into the shop. If I were to put a little fan on the floor blowing into the shop, that space next door would begin to warm up. If the opening went all the way to the ceiling, warm air from the shop would find its way in there and begin to warm it from the top down. Configuration of the physical environment is everything for air movement. If it's not conducive, then we have to coax it with other means. Rick
  22. burntime

    burntime New Member

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    Makes sense Rick, as others have said I run my ceiling fan to pull the air up an on medium. I have burned 2 out in 9 years!!!
  23. rfalk

    rfalk New Member

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    I am also in the process of installing a Declaration in my 1927 Tudor here in Wisconsin.....I have a cold air return about 10' from the stove, so my plan is to run the blower of the stove at night with only the fan of the furnace running.....hoping to circulate heat upstairs, at least enough to keep the bedrooms at 60 degrees....will keep you posted if it works. bob
  24. Cluttermagnet

    Cluttermagnet Minister of Fire

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    This makes a lot of sense, intuitively. Pull denser, cold air out of the room and some warmer air flows in at the top to replace it.

    I'm starting to think in terms of 'two rivers of air'. I know it's not really that simple, but you'd have a cold river(s) of air heading towards the stove, a convection updraft at the stove, and a warm river(s) of air traveling along the ceiling away from the stove. The warm air is impeded by bulkheads between rooms and halls, but some warm air spills down and out past them.

    Yes, it makes more sense to me to try moving cold air only. I have a free standing stove out in front of a two-sided fireplace. I'm going to put a 'big' (20") box fan in the fireplace opening behind the stove- blowing cold air from the adjacent dining room across the back of the stove and the 6" horizontal stove pipe. I'll place a couple of other small Honeywell high efficiency fans in the hall in two places to bring more cold air in the stove's general direction. They will be drawing on the end of the house which has two bedrooms and a small bath.

    I'll have to look into the dining room ceiling fan. Don't know if it blows up or down. I'll find out. In any case, probably either direction, run at slow speed, should help.

    I'll make a sketch and post it here when I get to it. I'm heating only the upstairs of my rambler, no illusions about affecting the (finished) basement level with the stove located on the upper floor.
  25. begreen

    begreen Mooderator Staff Member

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    If you have a fast reacting digital thermometer you can witness this. With our stove in the new location, our house naturally convects, sometimes too well. The 1st floor has an open floorplan with large openings between rooms. With a thermometer at the top and bottom of the stairwell you can measure almost a 5 degree difference. If you place a candle on a stair the flame will lean towards the stove. Raise it to the ceiling and it goes the other way. Incense works well too for visualizing and smelling where the air currents take the heat.

    This summer I added a dividing arch that comes down from the ceiling about 15" to the place between the living room and stairwell to see if I can slow down the river a little bit. The bedrooms are upstairs and I like them a little cooler for sleeping.
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