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  1. #1
    Join Date
    Mar 2005
    Location
    Raleigh, NC
    Posts
    20
    I just bought a home that was built in 1940. It has an old oil furnace which employed separate return vents in each room of the home, all joined to one plenum box in the basement.

    My questions are in whether or not there are any down-sides to this design and if it's worth converting to one centralized return vent between the two floors. The walls are plaster and there isn't much room (if any) in the apparently hardwood studded walls. The upstairs bedrooms are in a former attic, hence no space above them either.

    My other question is in how to filter the air. I know about putting a filter rack on the furnace at the return air plenum, but what about at the return vents themselves? Their sizes are about the size of the supply vents.

    Thanks for your input!

  2. #2
    Join Date
    Apr 2003
    Location
    Iowa
    Posts
    763
    Yap about that size..... you need enough return according on your furnace blower size.. Obviously if you have 1200 cfm you'd want 1200 cfm going in and out... you can put returns in the floor if you don't the walls..... but works a lot better if you put them in.... Another problem you'll find is that usually oil furnaces that old are usually under ducted on the supply too and you'll need to add more or modify them too.......

  3. #3
    Join Date
    Mar 2005
    Location
    Raleigh, NC
    Posts
    20

    Goodman GMS9

    I will be replacing this old furnace in this two story, 1525 sq. ft. home home with a Goodman GMS9/12 SEER 3.0 ton furnace/condensor.

    Besides having issues with maintaining temperatures, what are the other symptoms of under-ducting?

    Stetson

  4. #4
    Join Date
    Mar 2004
    Location
    SE Michigan
    Posts
    17,894
    Short cycleing of equipment, uneven temperatures, iced up coil, noisy system, premature parts failure etc. etc.
    " Kill a Commie for Mommy! "

    - Colonel David Hackworth (1930-2005), Korean War Vet

  5. #5
    Join Date
    Mar 2003
    Location
    Cincinnati
    Posts
    7,977

    Re: Goodman GMS9

    Originally posted by stetsonw
    I will be replacing this old furnace.
    Are you doing this all by yourself or are you going to have help?

  6. #6
    Join Date
    Mar 2005
    Location
    Raleigh, NC
    Posts
    20

    The Plan

    I am installing myself (the rough stuff), then having a tech finish it up and go over my work. I already had someone come out and tell me about the right size and about what to look for in using the current duct-work (insulating, etc)

    So we're hoping it all comes together nicely. The home is all brick with plaster all over the walls. Windows are insulated. With that old (and likely VERY inefficient) oil furnace, it seems to hold the heat well. I'm installing a 93% 70,000 BTU furnace. The previous owners (an elderly couple) seemed content with the two window units that were in there. I'm installing a 12 SEER 3 ton condenser. Actually, the calculations I've had run recommend a 2.5 ton condensor.

    Hopefully the ducts can keep up as I've been told they "may." I'm hoping that the returns in each room will help the circulation that would otherwise be problematic with a centralized return.

    That HVAC-Calc software looks interesting!

  7. #7
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    you are lucky to have returns in each room!

    BTW, where are the supply registers? inside wall or outside wall?

  8. #8
    Join Date
    Feb 2004
    Posts
    2,597
    if the load calcs have come in at 2.5 tons , why would you even consider putting in a 3?

    what size blower is on this model of furnace? will it be the proper size for the available duct work or is replacing the duct work an option?

    you need to re -think your penny pinching ways. you may save money now, but will pay later.

  9. #9
    Join Date
    Mar 2005
    Location
    Raleigh, NC
    Posts
    20
    Supplies all seem to be on the inside walls with returns on the outside walls. I can tell by how the return plenum is connected to a long conduit that seems to wrap around the perimeter of the basement.

    This is a rental property. I am trying to save a penny now indeed; this is my first rental property. I'm okay with having to re-do it later when I expect to have more cash-flow to improve the system later.

    Somehow, I don't think what I'm doing will be that far off although it may not be the most optimal. But I'm pressed for time and money, which I can address at a later time.

    I have downloaded the HVAC-Calc software and will register it and use it. Perhaps I will follow the recommendations from the software in stages in the future. But I need this place rented soon. I'm trying to strike a balance between speed to market, short-term cost, and finally, longevity (in the form of a later cleanup/correction).

    Thanks for the input guys!


  10. #10
    Join Date
    Mar 2003
    Location
    Cincinnati
    Posts
    7,977

    Re: The Plan

    Originally posted by stetsonw
    I am installing myself (the rough stuff), then having a tech finish it up and go over my work.
    Good Luck.

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