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  1. #1
    Join Date
    Dec 2011
    Location
    Hiram, Ohio
    Posts
    221

    can I force my new furnace to be less aggressive?

    Modulating goodman, installed last spring. 80K BTU, and now I believe it could have been the 60K, based on how much it runs. Dang, tried so hard to get it right, and I think my tech did too. In the end, it was me who told him go with the 80K, because the numbers were just too close at zero degrees. And I knew not to oversize!
    Anyway, I do like the fact that I can use a hefty set-back, I like the house cool at night. But, during the weekend day when we are holding at about 69 degrees, it will come on and not go immediately to low fire, it will stay up at around 70% for quite a while. The manual says it will "learn" how to heat the house the best over time, so I would think it would know, based on cycle times, that once it is at temperature it can just maintain at 50%, or at least attempt to. I have the full communicating t-stat, and it never overshoots.
    This spring, he will be adding a 3-ton HP to the system, which will add the outdoor temp sensor. Will that have any affect on how the furnace acts (when it is cold enough for the furnace to run) Any thoughts?

  2. #2
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    THe heat pump should fill in the "Gap" for BTU output in warmer weather. So you'll have 30-36k BTU's on the heat pump, then it will transition to the furnace at around 40k. Actually, that makes the slightly oversized furnace almost ideal. Even better if you have a 2 stage heat pump, then it will run almost continously below about 40F, meaning there no real penalty for an slightly oversized furnace in this case.

  3. #3
    Join Date
    Dec 2011
    Location
    Hiram, Ohio
    Posts
    221
    the heat pump is a 2-stage! And I am looking forward to how it handles AC this summer. My old AC, 3 ton, same size as the HP, would cycle quite a bit unless it was brutal outside. And therefore I had temp swings and maybe not enough humidity removed on days when it wasn't so hot. I am looking forward to this new system.

  4. #4
    Join Date
    Dec 2004
    Location
    Grand Rapids, MI
    Posts
    625
    The outdoor sensor will help the gas side, because it knows how many BTU's the home needs for the out door temperature.
    luck dan

  5. #5
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,663
    So are you going to over size the heat pump also because it is two stage. What is your heat gain and loss at design?
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429

    3-ton 33,000 at 47'F, 20,000BTU/Hr at 17'F

    2,100 Sq. Ft Colonial
    NE Ohio

    Heat Loss =~ 700 BTU per Hr/ 1'F below Thermostat Set Point [70'F]

    Balance Point 33'F with
    Goodman SSZ14 3 Ton

    Page 22
    http://www.goodmanmfg.com/Portals/0/pdf/SS/SS-SSZ14.pdf
    Attached Images Attached Images
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429

    Thumbs up GOODMAN 3 TON 18 SEER

    GOODMAN 18 SEER 3 Ton HEAT PUMP

    49,000 BTU/HR at 0'F HEAT LOSS

    Page 16
    http://www.goodmanmfg.com/Portals/0/.../SS-DSZC18.pdf


    THERMAL BALANCE POINT 30.6'F ___ SECOND STAGE
    ____________________.. 39'F ......... FIRST STAGE
    ____________________ __________
    Attached Images Attached Images
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #8
    Join Date
    Dec 2011
    Location
    Hiram, Ohio
    Posts
    221
    so it sounds like the HP should run almost all the time in the mid-30's on low stage, correct?

  9. #9
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by troyport View Post
    so it sounds like the HP should run almost all the time in the mid-30's on low stage, correct?

    Correct. Keep in mind that solar heat gain and internal heat loads will reduce net heat loss. Net heat pump capacity depends on outdoor humidity levels which impact how often it defrosts. So from about 35-40F and below, the system will run almost continously unless your or using a lot of lights and appliances. A home entertainment center with a big flat screen can generate 3000BTU's of heat. So can a coffee maker is 3000 BTU's, refrigerator, toaster oven, 15 standard light 60W bulbs and so on.

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429
    Quote Originally Posted by troyport View Post
    so it sounds like the HP should run almost all the time in the mid-30's on low stage, correct?
    I couldn't tell you what stage it would Actually be in when it is in the 30's outside

    > 40.0654321 'F ... 1st stage !
    __ < 30.0123456 'F ... 2nd stage !

    It depends on the sun, clouds, moon, winds and stars, time of day, ...
    installation,
    and whether you have treated your HP Well.
    If you talk to it like a friend and wash it, the ole HP may just respond better.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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