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  1. #1
    Join Date
    Jul 2006
    Location
    Las Vegas
    Posts
    34

    Hmm

    Hello,

    I was told by my Las Vegas AC system installation manager last week that it is normal that my new 3 ton two-stage Lennox 19 seer condenser will cycle on more frequently, and for less duration than the old replaced system did. It is paired with a variable speed blower. He said that my two-stage condenser unit may run more frequently for less time, but it will typically be at the lower speed, or first stage, 80% of the time. He said it should only be going to second stage(high speed) when it gets very hot outside (100+ degrees), or when the thermostat set-point has just been lowered a few degrees. He also says that at the lower fan speed/first stage, the unit is essentially operating at a lower tonnage equivalent, by almost half the 3 ton rating of the unit. He says that is why the manufacturers have no need for 1/2 tonnage condenser sizes with the high seer, two-stage units. Is this statement true?? Is my system still possibly oversized for 1,165sqft ya think? We have double pane glass, but minimal insulation elsewhere on our single level house. thanks.

    Ken

  2. #2
    Join Date
    Jun 2006
    Posts
    628
    Sounds about right to me, what size you need requires a load calculation of all the heat sources and square footage is just tip of that iceberg. If it runs the way he says it should, cycling, but on most of the time on hot days, then size sounds right as well regardless of the numbers used to get it.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,770
    Generally 2 stage units run for longer periods of time,not shorter.

    Did they install a new thermostat.

    If they did, they may not have set up the stat prpoerly.
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  4. #4
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    Originally posted by danglerb
    Sounds about right to me, what size you need requires a load calculation of all the heat sources and square footage is just tip of that iceberg. If it runs the way he says it should, cycling, but on most of the time on hot days, then size sounds right as well regardless of the numbers used to get it.
    are you basing this on the number of a/c units you have sized and installed?
    FILL OUT YOUR PROFILE!!

  5. #5
    Join Date
    Dec 2004
    Location
    Derby City
    Posts
    3,958
    beenthere has the correct answer here. Find out what the load calculation was for the home, and that will tell you if the correct sized system is in place. There is a whole lot more to it than square footage and glass my friend. Your system may be operating properly, however, you may have been given some incorrect information. Or on the other hand, you may must have a botched installation. Oh well, if you want to spend a lot of money with someone and then not go to THEM with the questions that THEY need to be answering, don't know what to tell you. What has THEIR response been other than to tell you it's working right? Ask to see their load calculations. All the best, John.
    Everyone has a purpose in life..........even if it's to be a bad example.

    Seek first to understand, before seeking to be understood.

  6. #6
    Join Date
    Jul 2006
    Location
    Las Vegas
    Posts
    34

    Unhappy

    He said no load calculation was required...they do these houses all the time, and this is the proper size for it based on windows/minimal insulation/etc. No real load calc was ever done, but perhaps I should have found someone to do it properly, and paid them for the service. Perhaps I can still have that service done, and if my contractor was way off on sizing, work a deal to have them bring in the next smaller size unit, or whatever the appropriate unit should be. The next two-stage unit down in size they would have is a 2 ton, and not sure if that tonnage might be too small for the house possibly?? Maybe just right?? I always have the BBB and legal avenues I suppose, if I really can prove this was a snow job on their part.

    Ken

  7. #7
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    DO THE LOAD CALC YOURSELF. it's at the top of the page. i'll bet you are oversized. unless you don't have a roof.
    FILL OUT YOUR PROFILE!!

  8. #8
    Join Date
    Jul 2006
    Location
    DFW
    Posts
    2
    You can also do a basic calculation here - http://www.mrhvac.com/loadcalcshortform.htm

    I used this one and came within a few % of the real one done by a professional.

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