Results 1 to 8 of 8
  1. #1
    Join Date
    Feb 2008
    Location
    Lucas, TX
    Posts
    107

    When is a 2 stage system good ?

    What's good about a 2 stage vs a 1 stage. A friend got a 2 stage system - with a gas furnace. I recently purchased a single stage heat pump.

    Thx.

  2. #2
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    One thing that's good is long runtimes on 1st stage, usually leads to greater comfort. If you have no complaints about comfort, that might not apply to you but it applies to many homes. Another good thing is a 2-stage AC such as the Trane 19i will have considerably better energy efficiency on 1st stage. I am a homeowner and like mine.

  3. #3
    Join Date
    Feb 2008
    Location
    Lucas, TX
    Posts
    107
    How is the 2 stage system sized? Is the first stage sized to 90% design temp and the second for the rest ? So its more for comfort than for energy efficiency ?

    Thanks.

  4. #4
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    For all that I know about, the 2nd stage is sized to the design load. Then whatever fraction 1st stage is, is decided by the engineers that designed the thing in the first place. The Trane 19i has two entirely separate compressors, and the 1st stage seems to be chosen about 55% of the 2nd stage size. The Trane 16i and many others have one compressor that can operate at two capacities, they seem to usually have 1st stage sized about 65-70% of 2nd stage.

    Because these units are generally only made in whole ton sizes, there is a greater tendency to oversize. Contractors always say to me it doesn't matter, and for sizing purposes they probably are right. One angle though is airflow thru existing ducts, often the original ducts are undersized for the original system, and become even more so when the system is upsized. Any bad effects would not show up on 1st stage but only on 2nd.

    These AC systems are *sold* more for comfort purposes than efficiency, because the high initial cost makes it hard to justify on a dollars and cents basis. However they are top of the line and almost always have a better SEER number than single stage units.

    There are 2-stage furnaces too, but we are not talking about those are we?

    Hope this helps -- Pstu

  5. #5
    Join Date
    Feb 2004
    Posts
    2,597
    A two stage system, be it a furnace, condenser or heat pump is designed for comfort only. (more even temps, more humidity removal in summer, more humidity supplied in winter, more filtration, etc...)

    As far as efficiency goes, everything is equal, your system will need to add or remove BTU's,if it does it at a slower rate it will run longer, but still use the same amount of fuel.

    i.e. a two stage 82% furnace will have the same AFUE rating as a single stage.

  6. #6
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,559
    Price is one obvious difference. Both will probably keep you very comfortable. It's like a BMW compared to a Ford. Neither are bad, but one is a bit nicer with more features.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,085
    2 stage is sized the same as a single stage.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Anytime the sun rises in the East and sets in the West. When ever the load diversity exceeds 30%. When ever you want to reduce the percentage of the time the system is actually oversized. When ever zoning is needed.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event