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  1. #14
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by spartantuck View Post
    I did have a couple of contractors think the duct from them main return duct work to the furnace was too small for a variable speed. One wanted to expand the end portion and one wanted to replace that whole duct with a larger one from them main return air duct work. The second option made more sense to me. Could just expanding the end do the job?
    They "thought" the return duct was too small for a variable-speed blower?

    #1. It either is (too small) or it isn't.

    #2. If the ductwork is too small, it will effect the performance of any motor.

    Many people think the variable-speed blower will compensate for a lousy duct design, this is true to a degree, but it doesn't make it right.

    I'm not sure as to your explanation of "expanding the end portion of the return duct".

  2. #15
    Sorry it took so long to reply, we had the flu go thru the house.

    What I was trying to say is the part of the duct that comes off the main cold air return that is on the ceiling of the basement (the trunk?) thru the air filter to the furnace. Both contractors think that bit of duct needs to be expanded for the variable speed fan.

    Sorry for the bad terminology but I am a new to this stuff.

  3. #16
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by spartantuck View Post
    Sorry it took so long to reply, we had the flu go thru the house.

    What I was trying to say is the part of the duct that comes off the main cold air return that is on the ceiling of the basement (the trunk?) thru the air filter to the furnace. Both contractors think that bit of duct needs to be expanded for the variable speed fan.

    Sorry for the bad terminology but I am a new to this stuff.
    The flu is going around! It's the pits. I hope the family is better.

    The ductwork that runs horizonally on the ceiling is a trunk line, correct.
    The vertical duct to the side of the furnace is the return air "drop".

    Yes, that piece of duct can be too small or it could be the filter (in the boughten boot) that is to small, say.....16"x20".....perhaps?

    Did the contractors also check all the returns in the house to make sure that there are enough?

    Again, lack of return air and "variable-speed" blower have nothing to do with each other per say. A regular motor would have the same issues.

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