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Moving the heat!

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Squiner, Aug 29, 2009.

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  1. Squiner

    Squiner New Member

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    The system will not affect the draft of the stove. The negative pressure in the room with the stove is being equalized by the positive pressure from the back of the house. The net pressure of the house does not change.

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  2. ckarotka

    ckarotka Minister of Fire

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    I tried something like this. I took one 6" insulated duct from the corner in the ceiling where the stove is and ran it about 15ft to the ceiling in the bedroom. I then cut a equal sq in hole in the wall as close to the floor as I could get for a return air. Mt bedroom is a converted garage by previous owners and is isolated from the rest of the house (for now). The system doesnt produce great results but it takes the edge off the room. So for the best I got was about 65f when it was 30f outside. I think the fan cools the air too much and am going to try switching the fans. blow the cold air out and let the warm air be drawn in at a slower rate. Hang a thermometer on the outlet to see how warm the air is coming out. If it's 85 going in how much heat do you lose?

    I have positive results from the small fans on the floor in the other bedrooms that works wonders.
  3. bsimon

    bsimon New Member

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    Glad to hear its working for you. I sometimes use the air handler ( a/c blower) to do the same thing. This week's project is adding a steam humidifier to the setup to 1) humidify the house and 2) move the air around the house periodically, instead of leaving the fan on when I'm burning.
  4. EL DRIFTO

    EL DRIFTO New Member

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    i set a pan of water on top for humidity.

    perhaps we'll all die from co cause my electric dryer is dumping inside my house now too.
    you can buy a box @ Lowes designed for this.

    you can switch fan directions, but i bet you'll keep it pushing hot air into the bedrooms,
    when you don't get hit by a water fall of cold air coming down the stairs, you'll know the bedroom is warm.
    which would be a good time for a normal hvac thermostat to shut the fan circut off over 73.

    in my system, i set up a second thermostat, in the same circut, in the ceiling. (on ac of course so it comes on when it's too hot up there)
    it keeps the fan from running continuously & only if there's substancial heat there in the ceiling area, mine cycles if the stove isn't roaring.
    it's drafty if the fan's on continuously.
    your system should be thermostatically automatic.

    as far as the heat loss, def insulate the attic stuff.
    since the air in the vent isn't as hot as a gas furnace hvac, the temp differential wont have you loosing as much heat in the attic, but still.
    i wish you could of ran it all inside.
    my inlet temps r 90 & it doesn't feel that hot coming out, but it definately works

    subscribded
  5. oconnor

    oconnor Minister of Fire

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    Squiner - glad it is working for you, but from a system design point, moving the hot air out of the room is not the best option. Doesn't mean it won't work for you.

    The very fact that cold air is returning into the room means you have created a pressure differential in the room where the stove is. That may not mean that you will draw CO from the stove, but you have created a relative low pressure area in the room with the stove. The wind only blows because of pressure differential.

    Edit - if you close one of the doors to a room recieving air, that room will pressurize, and with no air leaving, depresuurize the source room until the fan can draw/pull no more air - you will have a new equilibrium, with high pressure after the fan, and low pressure before.

    I assume that you have made sure that the intake vent in the living room is at least the code required minimum distance from the stove. I don't recall the numbers, but there is a specified distance to avoid problems. Again, this only matters from an inspection/code perspective - may not be a concern for some.

    Again, glad the system works for you, just want folks to be aware that there are some best practices at play that aren't respected in the design. In a different home config (i.e. basement stove in a two storey house), significant issues could result.
  6. mike1234

    mike1234 New Member

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    I think I would try to reverse the fan, just to see what the results were that way. Maybe worse, maybe better, but if it is not too difficult to do, might be worth trying.
  7. Hurricane

    Hurricane Minister of Fire

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    Squiner

    I asked the question on here before trying it, and most said it would not work.
    I have a raised ranch with a finished basement. My stove is centrally located on the top floor and I have no problems heating the entire 2400 sq ft upstairs with the stove. finished basement is not even half the upstairs size. My heating system is a single zone forced air system with the thermostat in the hall at the edge of the room with the stove. So when the stove is going the heat will never run, that causes the downstairs to get cold when the stove is running 7X24. I have an open staircase to the basement in the room with the stove and wanted to pull some of the heat from the ceiling down to the basement.
    Here is what I did for a test.
    I cut in a return register down the hall from the stove not too close to cause pressure issues ( about 20 ft away ). I used the wall cavity as the duct and cut the inside of the wall open downstairs and boxed it out with a 6" duct connector. I bought a 6" insulated duct at HD and ran the duct from that connector to the far end of the basement above the drop ceiling and just left the end hanging down for the test. I took the fan from my radon system and installed it in the duct for the test. I think it moves ~ 270 CFM. Last week we had a few colder days and I turned the heat off and started the stove it went down to 34 outside and I had the stove and fan going all night. Next morning I checked the digital thermometer downstairs and it was 71 degrees at 40 inches above floor. When the stove was burning hot you could feel the warm air coming out of the pipe downstairs. My total cost for the test was about $40.
    I tried using the fan on the heating system but I think the air just cools down too fast in there and it never really helped.
    Now I have put the decorative grill upstairs and a 2 X 2 diffuser in the drop ceiling downstairs, the fan should be coming today and I should be set. I like the idea of having the fan thermostatically controlled, but for now it will be on a switch. I bought a fan designed for constant use with about 240 CFM rating. Total cost now is ~$175 and it seems to work, if it only takes the edge off when it is real cold well then OK but from my test it seems like it will do more once the fan and stove are running constantly.
  8. GlacierBay12

    GlacierBay12 New Member

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    We have a cape style house. The woodstove is located in a family room off one end of the house with a cathedral ceiling. We have tried a number of approaches to move the heat. But last year we found that the best solution was to simply open a window on the far end of the family room just a crack and also open a window in the upstairs furthest most bedroom, thereby creating a natural convection current. Works much better than the fans we used previously, plus no noise.
  9. Squiner

    Squiner New Member

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  10. Squiner

    Squiner New Member

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  11. oconnor

    oconnor Minister of Fire

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    Essentially, no, it isn't the same thing. Think of the air movement more as water within piping in a closed system - yes, you have not changed the total amount of fluid (in this case, gaseous air) in the system, but it is pressure changes that are moving it. Pressure increased in front of the pump, and decreased behind it. The ceiling fan does depressurize part of the room, and raises pressure in another part, depending on what way you run it. All fans/propellers do. Your house can be seen as a closed system full of air. if you move air from one place to another, you need pressure changes. That is what moves the air to begin with.

    All that doesn't mean you will have problems - just making the tech point that pressure changes are happening. Were it my system, I would move cold air to the room where the heat is, increasing pressure in the stove room, and let the naturally bouyant warm air move itself. Best to align the pressure changes in favor with the process invovled - in this case, your stove is exhausting about 25cfm of air from the room, and the fan is moving air out of the room too. I'd sooner see the two forces working together.

    Enjoy your setup - I'm sure it will keep you warm and safe.
  12. Squiner

    Squiner New Member

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    Then what are you saying no to?
  13. oconnor

    oconnor Minister of Fire

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    I am saying no, it isn't the same as a ceiling fan. The ducting you have set up is deceasing the relative pressure in the room. Probably not enough to be a big problem, just feel it would be better if you added air to the room instead of removing it.
  14. EL DRIFTO

    EL DRIFTO New Member

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    it's like rocket science
    slam the bedroom door shut
    put a towel under it
    open the bedroom window
    turn the fan on high

    presto, negative pressure on the chimney!!!

    plumb in the stove inlet outside, end of problems, if you close the door
  15. westkywood

    westkywood Feeling the Heat

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    This is how I did mine. I have a thermostat behind my stove that is wired to 3 fans. The thermostat kicks on when the temp gets a certain temp then kicks off when the stove cools. I have a 12x12" vent in the ceiling above the stove which is attached to 10" flex duct in the attic. It goes 20ft to a junction box that has a 10" 650 cfm fan in it. It branches off to two 6" ducts with 6" fans in them. I tried using a smaller cfm fan but it just wouldnt pull much air so I went with the 10" 650cfm then the two 6". I totally buried the duct work in the attic with insulation.
    If I aim my IR thermometer inside the vent in a bedroom, it reads about 97-100 degrees. It hasnt got very cold here yet, so the real test is yet to come. My stove is in the living room at the end of the house. This really helps distribute the air. My daughter left her bedroom door closed the other night when it was about 40 outside. She said she woke up hot. She gets enough return air from under her door I guess.


    [​IMG]
  16. Squiner

    Squiner New Member

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    Nice setup. Glad it works for you.
    WellSeasoned likes this.
  17. semipro

    semipro Minister of Fire

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    o'connor,
    I don't mean to drag this out but I have a genuine interest in this issue and I'd like to understand better. I don't disagree with the premise that moving cold air to the heat source is more efficient than moving hot air away from it.

    What I'm trying to understand is what is the concern of creating negative pressure in the room with the stove in this situation? The pressure differential created by the air handler is with respect to the inside of the house not the outside. Since no mass is either leaving or entering the building envelope because of the added air handler the pressure the stove sees with respect to the outside is unchanged. So the interior circulation system should not increase the likelihood of CO release from the stove right to the inside of the house right????
  18. oconnor

    oconnor Minister of Fire

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    In fact, the pressure the stove sees with respect to the outside has changed, and it could in the right circumstances overcome draft. In a single level home like the one discussed in this thread, it isn't likely, but in other situations, the likelihood is different.

    Imagine a two story house with a wood stove in the basement. Simply heating the air in the basement will cause a pressure differential in the house, with buoyant air rising creating a pull on the heavier cold air - this is called stack effect. Stack effect alone can cause flue reversal. If you were to add to that an air circulation that also worked in favour of moving air out of the basement, you are in essence increasing the relative negative pressure that is seen by the stove.

    This actually bit me once when I reloaded a basement stove, and went to bed. I had a large fan blowing air out of the basement. When I left, the fire was building and looked as though it would go fine, but 30mins later, the smoke detector was ringing, and the basement was full of smoke. All of the possible "bad" vectors had aligned - cool flue, cold stove, stack effect and air circulation - to give me the worst case scenario. All I had to do to get the stove to go was turn off the fan and open a window, and the stove lit up real quick.

    If you want some reading on stack effect and the cons of using fans and air hoods to move air out of the room the stove is in, give the "Guide to Residential Wood Heating" link in my signature block a read. PM me as well if you have a scenario to look at.
  19. Lumber-Jack

    Lumber-Jack Minister of Fire

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    Actually Brent there is a section in that "Guide to Residential Wood Heating", under the subsection "Distributing Heat from Space Heater" that advocates using a ducted distribution method very similar to the one described by Squiner at the beginning of this thread. That of installing grilles on the wall at ceiling level and using a air circulation fan (or central heating furnace) to "suck" the hot air from the from the stove room to distribute to colder rooms around the house. It says nothing about blowing air into that room as you have suggested.

    Here is the diagram from that book that goes along with it.
    [​IMG]
  20. oconnor

    oconnor Minister of Fire

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    The diagram includes the system moving air back into the room via the same system. It also says this:
    "It is important, however, that the flow of air into and out of the room
    through the ducts and registers is balanced."

    and it says this:

    "CAUTION Never attempt to use a wood stove as a central
    furnace by putting a hood over it and connecting a furnace
    duct to the hood. This practice not only violates the building
    codes, it also disrupts the air-moving system and can cause
    the stove to spill smoke into the room. The biggest danger is
    the possible reversal of chimney flow that can quickly fill the
    house with carbon monoxide which can be hazardous"

    Stay warm and burn safe
  21. Squiner

    Squiner New Member

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    Thanks for pointing that out. I haven't had a chance to read all the way through that document yet.
  22. Lumber-Jack

    Lumber-Jack Minister of Fire

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    Of course the diagram is simplified for understandability.
    C'mon, how many house have only two rooms, an upstairs room and a downstairs room??? And what would be the point of sucking air out of the stove room, throught the down stairs furnace, and blowing back into the same room again?
    It is the air flow direction and grille placement that they are trying to exemplify in the diagram, and that the warm air is being moved to another part of the house.

    Nobody in this thread is placing a hood over their stove, that is quite a different topic. That's kind of like sticking a vacuum cleaner near your OAK inlet, vacuum force increases in relation to proximity.
  23. Lumber-Jack

    Lumber-Jack Minister of Fire

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    For the record, I think blowing air into the stove room would be a good thing to do too, (possibly a fan on the ground), along with Squiner's system.
    I just think it's best to get the warmest air to the coldest places you want heat first, and as quickly as possible.
    Besides, I think the air would naturally want to flow the way he has the fan going anyway. Always best to go with the flow. Easy way to find out which way the natural convection is, just don't run the fan, crank up the heat in the stove, and feel which way the breeze is going through the ducts.
    Can you try that Squiner?
  24. Squiner

    Squiner New Member

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    I can try that, i'll report back when it's cold enough to use the stove again.
  25. oconnor

    oconnor Minister of Fire

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    Actually, in the system they describe, air is being added to the room - pressure is higher on the outlet side of the fan - and they emphasise a balanced system. The system they descibe will remain balanced regardless of doors being closed or other factors, and has been installed by a heating contractor to take the issues at play into consideration.

    My issue isn't the movement of warm vs cold air, but the pressure effect on the room the stove is in. In the desrciptions from the guide (it is only a guide after all), the system is balanced - air volume leaving is equal to air returned via the system. Any of the systems I have read in the descriptions above don't have a dedicated return to ensure make-up air to the room the stove is in when doors are shut. If they were pulling air from distant rooms and moving it to the room with the stove, I would see no issues with the lack of makup air, as the pressure decrease wouldn't be in the room with the combustion appliance.

    If you want to make sure the system is safe, try this simple test - with no fire burning, close the doors, start the fan running, and see how the chimney flows after about 15 minutes. Then try lighting a fire - see how that works. If you are happy with the performance, good to go. If not, perhaps an OAK will assist.

    Please don't take me as argumentative, my goal is clarity not to change everyones mind.

    I don't think I can any more value to this thread. Anyone can PM me if they want to discuss further.
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