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step up on compressor to 2 stage worth it for Hi Vel Unico air handler??

Installing 2 zone central AC on old house with steam heat- Unico air handlers and Lennox xc14 outdoor units. 2 ton downstairs, 4 ton on third floor. Current quote is for AC only. Current steam heat works well -has massively oversized 50 year old boiler. Contractor says AC system alone will probably be a bit more reliable than using a heat pump. Quote started with 14acx compressors until I pointed out the longer warranty and quieter unit. Contractor seems like a good guy.

Would it make sense to go to xc16 compressor (2 stage) from an XC14 with a Unico system - or is there no possible gain in efficiency? Thanks!!


  • John Mills_5
    John Mills_5 Member Posts: 951
    Hi velocity air handlers kill SEER. Some cases you can take a 16 or higher outdoor unit and end up at 11. You can look at the ratings on AHRIdirectory.org and see if it helps but likely not. Also look at what the system does with your capacity. Your "4 ton" could end up much less than 48,000.
  • ChrisJ
    ChrisJ Member Posts: 15,688
    edited April 2017
    I agree with everything John said, but want to add I was unable to find any published info regarding 1 stage vs 2 stage and efficiency.

    It seems to be very difficult for anyone to answer for some reason.

    As long as the air handlers are matched to the outdoor unit using AHRIdirectory.org I wouldn't hesitate to use a 2 stage outdoor unit. There's a good chance your contractor doesn't quite understand it either.

    I suspect in real life, 2 stage will run quieter and slightly more efficient most of the time (low stage).

    But good luck finding any good hard evidence in writing.

    Just an FYI, you may need to fiddle around with the AHRI website a bit to get it to work. It took me a while of changing different selections and I finally got it to work for my stuff. My 16 SEER outdoor unit runs at 15 SEER when matched to the air handler I picked. The only way to go higher was to get an oversized air handler that would've increased my sensible cooling, which was the last thing I wanted.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Koan
    Koan Member Posts: 439
    @John Mills Thank you for the input - I know I will be taking a hit in SEER, I just wonder if the 2 stage will make any meaningful difference. In my case it is an old house so regular ducting probably does not make sense.

    @ChrisJ I have been looking for information on that as well. I don't want to push the contractor to install better more expensive equipment unless it makes a difference.

    Thanks you both for the information.