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  1. #1
    Join Date
    Oct 2007

    One more set of pre install questions

    I have gotten a ton of great advice here and am all set to start a replacement tomorrow morning.

    I am getting a carrier infinity system, the only challenge now is sizing.

    The salesperson did run a manual J, and the recommendation came back at an 80k BTU furnace (this is replacing a 100k).

    Here is where it goes a bit sideways,

    We were all set to go for the 2 stage 96% unit and he called me on friday and said I need to look into the new 3 stage that they just got in the past week. I had heard about it here and it sounds like it would really be good for our application (2 zones, one 700 SQ feet, one 1700 sq feet) but the sales guy wants to go back to the 100k unit because he didn't feel the smaller unit would ever go to the third stage.

    Does this sound normal? I am comfortable with everything else that I have heard from this company, just want to make sure that I get the right sizing.

    I am leaning towards the smaller unit simply because it would be right for our environment. Does the infinity zoning change the sizing at all?


  2. #2
    Join Date
    Aug 2007
    IF the load calc says 80K you put in an 80k staging doesn't change the required BTU's, the 100k would be the one to never go to 3rd stage, If he feels the 80k will not go to 3rd stage that means you need a 60K. Sounds like its a good thing that salesman just sells and isn't the one installing the equipment.
    You can't fix stupid

  3. #3
    Join Date
    Oct 2007
    so get the 80k?

    His other point was a 100k would heat up the house a lot faster at the initial run. Something that I am not that concerned with.

    the sales guy said that the three stage (Carrier ICS) would never go to the low stage because of zoning. He feels that the second (downstairs) zone is so large that the unit would only ever run in medium and high and never in low. But a 100k would somehow go to low.

    We live in a 12 year old custom house with good insulation, in California and it gets below freezing very rarely (two or three times a year) but is cold and foggy a good portion of the year.

    My gut feeling said that if the load calc was 80k then that would be the suggested unit size. But for 2500 SQ feet?

  4. #4
    Join Date
    May 2000
    Indianapolis, IN, USA
    Multi stage is no reason to oversize. Trust me, I know. At the time the mfr didn't make the size I needed so I went 20K oversized. Might as well not have high fire. Stick to the 80K that you need. Hopefully you are getting the Infinity control.

  5. #5
    Join Date
    Oct 2007
    Yes on infinity and I will go 80k.
    I will post a follow-up once they complete the job.

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