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  1. #1
    Join Date
    May 2004
    Posts
    44

    Carrier 95% furnace, and return air question?

    Does this sound acceptable to you guys?

    Due to factory rebates and dealer discounts and the 30% Federal Tax credit, a Carrier Infinity system 2 ton ac (Infinity 17) with the 95% 58MVC060-14 furnace is actually cheaper than other options with an 80% variable speed furnace and a Performance Series AC unit (at least from this particular dealer).

    However, the salesman says that the 95% furnace is very sensitive to return airflow. The furnace is located in the basement and services the first floor of my two story house. There is one return on the first floor. It's about 24 inches x 6 inches. The salesman is suggesting putting a 2nd return in the basement to insure proper airflow back to the furnace.

    It seems to me that instead of heating the first floor, I'll now be heating the basement also since the only way to pull air into the basement is from the first floor.

    Is this a common solution? I'm not sure I like the idea of a second return on a different floor for a system that is supposed to be for the first floor only.

    The 95% furnace is really overkill, our gas bills are low already, but like I said at the beginning, it's actually cheaper than some of the other options with lesser grade equipment. However, I'm worried about the fact that if I end up heating two floors with the 95% furnace, my gas bill may not be any cheaper than it is now, even with a more efficient furnace.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,601
    Why can't an additional return be added to the first floor.

    If you pit more return in the basement then you are suppling. You can put the basement into a negative pressure.
    And if you have a gas water heater, that vents into the chimney, you backdraft it, and pull combusted gas(possibily Carbon Monoxide) into the house.
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  3. #3
    Join Date
    May 2004
    Posts
    44
    Quote Originally Posted by beenthere View Post
    Why can't an additional return be added to the first floor.

    If you pit more return in the basement then you are suppling. You can put the basement into a negative pressure.
    And if you have a gas water heater, that vents into the chimney, you backdraft it, and pull combusted gas(possibily Carbon Monoxide) into the house.
    I'm assuming the guy is trying to keep the price down on the quote, probably figuring I'll be getting multiple quotes and will only be eyeballing the bottom line. If I'm going to go to all this trouble, I want it done right. I've got a second dealer coming in this afternoon to get another quote, I'll see what he says.

  4. #4
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,025

    Return Air in basement won't help airflow on other floor areas.

    If you live in the basement, & the combustion air systems are in a sealed off room, with adequate access to outdoor air, it is okay to put a Return Air in the living area of the basement.

    Normally, the Return Air should be on the floors you are heating where it will actually improve airflow & heat to those areas.

    You seldom need a Return Air in a basement that is below ground level.

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  5. #5
    Join Date
    Jan 2006
    Location
    Powell River, BC, Canada
    Posts
    763
    Your guy was right, that single return is too small. Also the sensitivity to airflow applies to MOST high efficient and newer 80% furnaces. The increased efficiencies of modern furnaces are partially due to thinner/lighter materiels used for the heat exchangers for better heat transfer. They are thus alot more sensitive to overheating due to lack of airflow from undersized ducts and restrictive/dirty filters.

    The question of where to put the new returns will depend on how your house is laid out. It's not a bad idea to have some supply and return in the basement. As Beenthere mentioned, dont pit more return than supply if there is a natural draft HWT in the space. Is the basement finished at all, or used at all?
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  6. #6
    Join Date
    May 2004
    Posts
    44
    Well, turns out there is a second return on the main floor, in the living room up in a corner near the ceiling. I'd forgotten about that one since we seldom use the room. The existing system has two return ducts going into it. I checked the unit yesterday and when I saw those two returns I remembered the return in the living room.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,601
    Still may not be enough return.

    Wall cavities, don't allow a lot of air to travel in them.
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