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Air circulation question

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by karl, May 4, 2007.

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  1. karl

    karl Minister of Fire

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    I have a long narrow ranch styled home. Fortunately, the fireplace is in the center of the house and the living area of the house is fairly open. I am planning to install an insert in the fireplace. I am leaning towards the Napoleon 1402 insert. It has a 2.25 cubic foot firbox, which is the size everyone here seems to think would be best for me. Output is 11,400-41,300 EPA and 70,000 Wold Steel Ltd. It is rated for a 1,000-2,000 square foot house. My house is about 2400 square feet. So I'm thinking I might be a little on the small side. I don't really know. I don't need to heat totally with wood but I would like to heat as much as possible with it. I'm in Southern West Virginia and the winter temps are generally the 20's at night and the 30's-40's during the day. Anyway, I am concerned about circulating the air in the house and I would like to avoid running the furnace fan.

    My plan is to put two cold air return vents in the ceiling of the room the insert is in and then feed each one of them to opposite ends of the house through duct work in the attic. They would then discharge from the ceiling at each end of the house, to circulate the air. I would then put duct boost fans or something similar in these two ducts. Has anyone tried this before? How well did it work and is it something I really need to do?


    Thank you in advance for your advice

    Karl

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  2. Corie

    Corie Minister of Fire

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    It would probably work Karl, but what you'll have to think about is exactly how much warm air you'll have to move to actually see a difference in temperatures in the areas with the cold air returns. I think you'll find the number to be a little large, which doesn't mean its impossible, but that it may require more fan than you're thinking to overcome the duct pressure losses and still move a sufficient volume of air to transfer enough heat.

    The system needs to be balanced, at least in a crude way, because pushing 100CFM of cold air around probably isn't going to make HUGE difference in evening out the temperatures.



    Before you do anything though, I would recommend hooking the thing up, and letting it run for a while. See how things are, you might be pleasantly surprised at the way the temperatures even out. If they don't, then start making changes. But no sense fixing something before it's even broken.
  3. elkimmeg

    elkimmeg Guest

    Karl its m not going to work returns by code have to be atleast 10' away from a wood burning stove by removing necessary combustion air you risk backdrafting your stove
    that means drawing in deadly cabbon monoxide gass3s into the living space the using your Hvac system to rapidly spread them. Supplies with out returns or retuens with out ballance again will render t your existing system ineffecient and reduce it effeciency If you have ceiling returns you already have the least effecient design possible adding more does not increase effeciency. How do you plan to balance your system? That's right code compliant systems are required to be ballanced.. The key to heat distributiion is moving cooler air not warm air

    As a nationally certified Mechanical inspector I would require mechanical calculations and a mechanical engineere's plan and stamped to issue a permit for your alterations. I would alsoi require a complete balancing report of the revised system. Naturally no return can be within 10' feet of a solid fuel burning appliance per code I also would be inspecting supply = returnsm as required by code I would require calculations of how an inline blower effects the entire ballanced Hvac system. I would require flow rates re-calculated in all difusers to make sure the proper volumes are being dispersed in all rooms. Many have teied to use returns few have been sucesfull the only thing accomplished is reduced safety Let me ask you is your HVac system s designed and listed to be used in conjunction with a wood stove? If not then it is not code compliant you just made it so, non compliant without any safe guardss you increased the risk of safe exit of your familly I have to ask you are you willing to assume the increased risk? Should you and your familly survive an incident ,are you in a financial position you do not need insurnce to rebuild?
  4. titan

    titan Minister of Fire

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    Any benefits of heated air circulating through your attic ducts will be negated if the ducts aren't very well insulated and sealed.
  5. DiscoInferno

    DiscoInferno Minister of Fire

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    My EPA fireplace has a direct connection from its outer shell to flex duct that leads through a blower and into the house ductwork. Hot air comes out of the blower, but after mixing with the main blower and going through the house ducts I get nothing. Luckily my house distributes internally OK. You'd be starting with much cooler air, and I doubt you'd get much benefit.

    What has been discussed here at times is to instead move cold air from the ends of the house to the stove. This would then let the heated air from the center of the house flow along the ceiling into the ends. Some folks here just use floor fans for this purpose. You could also use floor ducts but that might violate code just the same as ceiling ducts.
  6. karl

    karl Minister of Fire

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    I didn't even think about affecting the draft of the insert. I guess that's why I'm here asking questions. Now this brings up another question, the outdoor airsupply. The stove says its a must have one in mobile homes but optional in convential homes. I have a tender box built into the wall next to the fireplace. It has a door in the front to take woood out of to put in the fireplace, and it has a door in the back to load wood from the outside. Therefore, it would be easy for me to connect a fresh air supply. How beneficial is an outside air source to a fireplace insert?
  7. Gooserider

    Gooserider Mod Emeritus

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    There is some arguement about Outside Air Kits (OAKs) based on the idea that under some very odd conditions they will flow backwards and potentially cause combustion gasses to go out through the possibly combustible OAK plumbing and / or hit the combustible home exterior. In fact there is little evidence that this ever actually happens, and less that any harm has ever come from it.

    That said, the amount of benefit you will get from an OAK largely depends on how tightly sealed your house is, and possibly how many other things there are trying to pull air out of it. (bath and kitchen exhaust fans, clothes dryers, the furnace, etc.) You want to have no major difference in the pressure inside the house and the outside. It's like a bank acount - air infiltration puts into the account, the stove, exhaust fans, etc. take out, and you want to have as close to a zero balance as you can.

    A new construction, tightly sealed home is likely to need an OAK to supply the makeup air, and codes in many places require them.

    An old leaky house is going to have less of a problem with makeup air, so it has less NEED for an OAK. However some folks like to put in an OAK anyways on the theory that it reduces the need for cold air to inflitrate and be rewarmed to make up for the room air consumed by the fire, and thus reduces cold drafts in the house.

    From an energy consumption standpoint they are theoretically a wash - you have to bring the air entering the stove up to temperature no matter what, and it doesn't make any real difference whether the air enters the stove directly or via way of the room.

    Bottom line, IMHO it won't do any harm, but I'm not sure how much benefit it will be.

    Gooserider
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