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  1. #1
    Join Date
    Jul 2006
    Posts
    151

    Heat pump BTUs for dummies

    I realize may not be providing enough information to have this answered, but I will ask anyways.

    I live in Winston-Salem, NC. Our house is a brick split foyer with ½ the basement finished and the other ½ a garage. It’s about 2100 sq ft. Decent attic insulation. We have a 25+ year old AC and a 14 year old 80% propane furnace. The AC is 3 ton. The furnace is 100,000 BTU. I am thinking about replacing everything with a heat pump.

    My question concerns the BTUs from heat pumps. If we get a 3 ton heat pump to replace our current system, will the heat output be approximately 36,000 btu? Even if I assume our 100k propane furnace is way oversized, 36k is a whole lot less than 100k. That's a lot of BTUs to lose.

    It’s entirely possible I am way off base on this, so please forgive my ignorance on this subject.

    Thanks,
    Bill M.

  2. #2
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Bill:

    You need a heat gain/loss calculation done on the home. It's called a "Manual J". I believe there is a calc that you can use on this site for a fee.

    A heat pump is typically sized for cooling. Additional btus for heating are supplied by auxillary or supplimental heat, like a furnace or electric resistance strips.

    A 3-ton heat pump will put out 36,000 btu at is rated outdoor temp, which is 47F outdoors. As the outdoor temps drop, the btus drop, and so does the temperature of the heated air produced by the heat pump.

    I believe that propane furnaces are rated at input btu's, so you have 100,000 x .8 = 80,000 btu output.

    Good luck.

  3. #3
    Join Date
    Mar 2008
    Posts
    657
    have you considered going dual fuel? assuming you don't know what it is, its when you keep the furnace and and a heat pump to the sytem. basically the heat pump does the heating until the outdoor temp. goes below 35 or 40 depending on set balance point where the heat pump is not as effective. this way your not using the propane as often. it kind of acts like the backup electric heat in a heat pump system. just an idea.

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428

    Angry 4-ton HP

    Quote Originally Posted by acobra289 View Post
    ... Winston-Salem, NC. Our house is a brick split foyer with ½ the basement finished and the other ½ a garage. It’s about 2100 sq ft.

    Decent attic insulation. We have a 25+ year old AC and a 14 year old 80% propane furnace.

    The AC is 3 ton. The furnace is 100,000 BTU. I am thinking about replacing everything with a heat pump.

    My question concerns the BTUs from heat pumps. If we get a 3 ton heat pump to replace our current system, will the heat output be approximately 36,000 btu? Even if I assume our 100k propane furnace is way oversized, 36k is a whole lot less than 100k.
    100K is simply
    TOTALLY Unrealistic
    unless you are talking about a 90+ year old (no insulation and holes) house.

    An ACCA Manual J calc may indicate that the heat loss is only 40,000 BTU.

    I might propose a 4-ton 2-stage heat pump.

    If you need some help, let me know.
    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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