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  1. #1
    Join Date
    Dec 2008
    Posts
    2

    Question Forced air heat duct work

    I have a few questions about my forced air heat system. The system is powered by an armstrong air Ultra 80 (125D20). The house is located in the adirondacks so the winters get cold and is roughly 2800 sq. ft.

    The furnace is located on the far end of the house. So it has a long run of duct work from one end to the other. I have found that the end close to the furnace gets warm while the other end of the house has lower pressure and colder air coming from the ducts. Causing cold rooms on the one end of the house.

    While trying to search for a reason for this I noticed that the duct work that makes a run down the length of the house starts with an opening from the furnace that is 1'-8" X 7". It then goes to a larger opening 2'-4" X 7". This continues for 10' or so and then jumps down to a 2'-0" X 7" opening. This also continues for another 10' or so and then jumps down to a 1'-5" X 7" opening for about 10' and then finally jumps down to 1'-1" X 7" opening and then terminates. Off of this run of duct heat is supplied to about 1600 sq. ft.

    Could the reason for the lack of pressure be from the fact that it starts with a small opening and then goes to a large opening?

    Would I benefit from adding two zones? If so, how hard would that be and what would I need?

    I would like to insulate and rerun some of the duct work. Does anyone manufacture insulated ducts? I have found the round insulated ducts at home depot and lowes but what about the rectangular duct work?

    Also I have a chimney located in the middle of the house. Would I benefit more by moving the furnace to that chimney?
    Last edited by kvs; 12-07-2008 at 06:55 PM.

  2. #2
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,836

    Default Re: Forced air heat duct work

    It sounds like a combination of poorly designed duct system and distance. If you think of it as a fan the farther away you stand the less air you feel moving, the longer the run the more duct metal to steal heat, and the constant changes in size creates even more resistance. Why do you need to stay with rectangular ducts, round work just as well. Centering the furnace, providing you don't use the fireplace , would help balance the resistive load. You may need to install a chimney liner as a wood fireplace chimney may be to large to accommodate proper draft. You might want to consider upgrading to a high efficiency furnace that can be vented through the side of the house through PVC pipe.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #3
    Join Date
    Dec 2008
    Posts
    2

    Default Re: Forced air heat duct work

    I have no problem using the round duct. If I were to go all round would I have one main one with branches coming off of it or would I have to have a bunch of round ones coming from the main trunk?

  4. #4
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,836

    Default Re: Forced air heat duct work

    It can be done either way, but if you use a main and split off to other runs with the flexible insulated pipe you will probably need to install splitter boxes of some kind. Don't forget dampers to help with balancing the system.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  5. #5

    Default Re: Forced air heat duct work

    Try to get the heating plant and the ductwork inside the heated envelope. That way, any air that leaks will still provide heat to the home, and outside air ...

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