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  1. #1
    Join Date
    Aug 2004
    Posts
    29
    Why is it that the SEER goes down with larger tonnage for a model line. It happens with all models. The most efficient are the 1-2 ton units. Least efficient the 5 tons. What are the physics behind this?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,917
    At a guess I'd say coil size. My 2 ton 13 SEER heat pump has an outdoor coil the same size as a 10 SEER 5 ton. In fact, back then Rheem used 2 coils & 2 fans to get that kind of SEER out of their larger units.

  3. #3
    Join Date
    Dec 2004
    Location
    Derby City
    Posts
    3,958
    baffin; an easy analogy is to look at mpgs in autos. Both vehicles will achieve 55 mph, but the 4 cylinder will do it more economically than the V-8. Much like engines the larger a/c units require more electrical usage, i.e. larger motors, compressors, etc. and that results in less efficiency. You have raised an important point, and that is to be sure what efficiency YOUR system provides, you need to look at the seer rating for the exact system you have. That would be the outdoor unit matched with a specific indoor coil would produce a specific seer. You will also find that some manufacturers will achieve higher seers for their units that others.
    Everyone has a purpose in life..........even if it's to be a bad example.

    Seek first to understand, before seeking to be understood.

  4. #4
    Join Date
    Jun 2000
    Location
    WYO
    Posts
    2,019
    I agree with irishmist, Same thing happens with High efficiency furnaces. AFUE goes down with larger model units.Some Co,s advertize 94% eff., but that may be the 40000 btu model. The 120000 btu model may be closer to 90%.
    never say never

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