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  1. #1
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    Default conjoined furnaces

    I've seen houses with two or three furnaces, but they were always separate. These two are joined together. Any illuminating comments would be appreciated.

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  2. #2
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    Default Re: conjoined furnaces

    My first thought is be that it's not going to be possible to balance both sides, and if there is a HE failure...

    Michael Thomas
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  3. #3
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    Default Re: conjoined furnaces

    So long as air flow, gas, venting is planned and executed properly, I don't see a problem. Very common practice in churches, etc. Some manufacturers used to provide conversion kits. There should be a common relay to ensure all blowers operate simultaneously to prevent counter flow back through an idle unit.

    Jim Luttrall
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  4. #4
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    Default Re: conjoined furnaces

    Quote Originally Posted by Jim Luttrall View Post
    ...Very common practice....
    Thanks very much. I mainly wanted to know exactly that.

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  5. #5
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    Default Re: conjoined furnaces

    You can refer to them as being twinned.


  6. #6
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    Default Re: conjoined furnaces

    Quote Originally Posted by neal lewis View Post
    You can refer to them as being twinned.
    Thanks. I was thinking of conjoined twins, like Siamese.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
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  7. #7
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    Default Re: conjoined furnaces

    I would think that without that center dividing panel, each blower is going to be sucking from the other blower ... install that panel and each blower will operate in the manner in which it was designed.

    Jerry Peck, Construction / Litigation Consultant
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  8. #8
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    Default Re: conjoined furnaces

    I would think that without that center dividing panel, each blower is going to be sucking from the other blower ... install that panel and each blower will operate in the manner in which it was designed.
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    Furnaces can be twinned to operate at the same time,,Staged to operate as needed with a zone damper to prevent air from bieng sucked back from idle unit. Either way the return is common to each unit.


  9. #9
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    Default Re: conjoined furnaces

    Bryant 394-B - Installation Instructions - Tandem Gas-Fired Forced-Air Furnace.

    A quick read (for example the separate return air openings in figure 3 and the note below installation step 1-5) suggests to me that these may not be intended to be installed with a cross-connected blower compartment.


    Last edited by Michael Thomas; 12-16-2009 at 08:48 AM.
    Michael Thomas
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  10. #10
    David Bell's Avatar
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    Default Re: conjoined furnaces

    A quick read (for example the separate return air openings in figure 3 and the note below installation step 1-5) suggests to me that these may not be intended to be installed with a cross-connected blower compartment.

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    Michael Thomas
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    That particular instruction booklet is from 1974, a few things have changed since then.


  11. #11
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    Default Re: conjoined furnaces

    Quote Originally Posted by David Bell View Post
    That particular instruction booklet is from 1974, a few things have changed since then.

    However, air still flows under the same laws of physics as it did back in 1820, with some revisions on the written understanding of those laws - nature did not change, only the human understanding of what happens and why changes.

    - Installation
    - - 2. Apply proper seal around return air openings to prevent air leakage. Apply sponge tape from accessory package to right side of base of control furnace. This provides an air seal between furnaces.
    - - etc.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  12. #12
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    Default Re: conjoined furnaces

    Did I mention that there was "oil canning" noise when the fans started up?

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  13. #13
    David Bell's Avatar
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    Default Re: conjoined furnaces

    Quote Originally Posted by Jerry Peck View Post
    However, air still flows under the same laws of physics as it did back in 1820, with some revisions on the written understanding of those laws - nature did not change, only the human understanding of what happens and why changes.

    - Installation
    - - 2. Apply proper seal around return air openings to prevent air leakage. Apply sponge tape from accessory package to right side of base of control furnace. This provides an air seal between furnaces.
    - - etc.
    The changes I am refering to are, variable speed blowers, improved controls for zoning, multiple stages of heat. Obviously a proper seal is required. but a common return is not always wrong.


  14. #14
    David Bell's Avatar
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    Default Re: conjoined furnaces

    Quote Originally Posted by John Arnold View Post
    Did I mention that there was "oil canning" noise when the fans started up?

    could be a lack of return,,could be a bad seal,,could be nothing but duct noise from air pressure.


  15. #15
    David Bell's Avatar
    David Bell Guest

    Default Re: conjoined furnaces

    Quote Originally Posted by Jerry Peck View Post
    However, air still flows under the same laws of physics as it did back in 1820, with some revisions on the written understanding of those laws - nature did not change, only the human understanding of what happens and why changes.

    - Installation
    - - 2. Apply proper seal around return air openings to prevent air leakage. Apply sponge tape from accessory package to right side of base of control furnace. This provides an air seal between furnaces.
    - - etc.


    By the way if you would like to have a heating unit from 1820 feel free to indulge


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