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  1. #1

    Furnaces with AC units

    Everyone would agree that if you have a gas furnace and an outdoor unit it's best to have both the same brand right? To assure proper sizing and seer etc.

  2. #2
    Yes your right. Make sure that whatever you get is a proper ARI matched system.

  3. #3
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,973

    Arrow

    If it is the usual upflow Oil furnace, make sure the evaporator coil is mounted at least 6 inches above the top of most Oil furnaces.

    The majority of Oil furnaces have a huge heat exchanger drum that comes close to the top of the furnace & the coil setting too close to it will restrict airflow causing a lot of back-pressure & turbulence; resulting in a huge drop in static pressure & air velocity on the discharge side of the coil.

    The airflow needs that static pressure & velocity at the diffusers to properly cool the rooms.

    Additionally, the coil will not have enough of a heatload going through it & cooling BTUH will drop like a rock.

  4. #4
    Thanks fellas, I'm working on a bid and they are having a lot of problems with ac's with eratic pressures and they have one brand of furnace with another condensor, life would be easier and equipment much better if it's all the same brand.

  5. #5
    Join Date
    Aug 2008
    Posts
    416

    Surprised of Lack of Responses

    Kind of surprised that more of the pro's have not responded to your comment...

    Not a pro, but I would say both "yes and no".

    Why "No"? For basic equipment where you're setting a fixed airflow of 350/400/450 CFM and when you think of the basic control wiring. Mixing a gas furnace from one mfgr with an AC from another would have little effect on performace... For a basic AC a coil wants to see so many CFM... As long as its aligned properly with the furnce and openings match, different brands shouldn't matter. To be clear, when I say AC I mean that the indoor coil and outdoor unit are matched from the same mfgr..Its the indoor gas furnace that is from different mfgr...

    Why "Yes"?? Now if you're talking higher end systems with 2-stage coooling and heating, modulating heat, along with humdity control, the same mfgr is probably the way to go... And if you're talking the new "communicating tstats", definitity same mfgr is desirable.

    That said, any combo can be made to work if you try hard enough.

    By way of analogy, think of your home computer. You have hardware from one guy, operating system from another, and applications from another. But, some play better together than others. Some prefer to get as much as they can from Microsoft, because the theory is that their applications (such as Office, Internet Explorer, Media Player) play together with the Windows operating system better than say OpenOffice, etc.

    In my opinion, I would always get everything from the same mfgr, but thats a "feel good" reason more than a technical opinion.

  6. #6
    Join Date
    Jan 2004
    Location
    Here and there
    Posts
    4,804
    as long as the airflow is a match who cares what brand furnace
    i belong to peta ... people eating tasty animals. all my opinions are just mine.

  7. #7
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,077
    Coil must match the outdoor unit to work the best.

    Jeff is right, as long as airflow is correct it doesn't matter what is blowing it.

    Til you get into SEER ratings that require a matching ECM blower inside. Once you get much past 13 SEER, the ratings look at the electrical usage of the blower to figure the high SEER. So if you are looking at higher SEER units, the ratings will reference what indoor unit the system should be matched with and then, yes, it does matter. But for SEER, not operation.

    For some years, we sold 1 brand of furnace and another brand of A/C since we felt that the 1 mfr had a great furnace but a pricey, noisy A/C. Our other brand had a great scroll compressor A/C. Always used a coil that matched the A/C.

  8. #8
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    Do we understand the question?

    a gas furnace and an outdoor unit it's best to have both the same brand right?I thinhk the home owner is talking about the furnace manufacturer and the AC having some brand, Not the indoor and outdoor units.
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  9. #9
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Confusion reigns!

    Let's be clear. There are 3 pieces of equipment involved.

    1. The blower (usually contained in the furnace of choice)
    2. The outdoor unit (condenser if just cooling)
    3. The indoor coil.

    The AHRI matched system will rate all 3 components. They may be the same manufacturer (matched) or you may find some mixed systems (mixed) also rated. The name on the pieces of equipment is irrelevant as far as operation, as long as the airflow is proper for the cooling equipment installed.

    For documented efficiency ratings, they must be as listed on the manufacturer's or AHRI website. Not being listed doesn't mean they won't work together, it just means you can't document the actual efficiency.

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