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  1. #1
    Join Date
    Oct 2012
    Posts
    6

    Confused Expensive electricity, cheaper gas -- what is a practical balance point?

    Before I start out, here are the specs on the equipment:

    Heat Pump: Lennox 13HPD-048-230-01 (4 ton)
    Air Handler: Lennox C33-49C-2F-3
    Furnace: Lennox G43UF-60C-110-8 (92.1% AFUE)

    Performance chart (closest I could find -- everything as listed above, but uses G60HV-60C-110 instead of my G43UF):

    F____C____kW in___kBtuh out___kW out
    65___18___3.28______57.0_______16.7
    60___16___3.26______54.3_______15.9
    55___13___3.23______51.6_______15.1
    50___10___3.20______48.8_______14.3
    47___8____3.19______47.2_______13.8
    45___7____3.13______44.5_______13.0
    40___4____2.99______37.7_______11.0
    35___2____2.84______30.8_______9.0
    30___-1___2.90______30.8_______9.0
    25___-4___2.95______30.9_______9.1
    20___-7___3.00______30.9_______9.1
    17___-8___3.03______30.9_______9.1
    15___-9___3.02______29.8_______8.7
    10___-12__3.00______27.1_______7.9
    5____-15__2.80______24.1_______7.1
    0____-18__2.60______21.2_______6.2
    -5___-21__2.41______18.2_______5.3
    -10__-23__2.21______15.2_______4.5
    -15__-26__2.02______12.2_______3.6
    -20__-29__1.82______9.3________2.7


    Cost of natural gas is $0.52 per therm
    Cost of electricity is $0.13 per kWh

    I've tried to figure out a realistic economic balance point for the system (it's a 4 year old house that I bought recently). Living in the Kansas City, MO area. From what I can figure out, it will cost me more to use the heat pump than to just use gas. I've read so many stories about heat pump efficiency and setting balance points that I have difficulty believing that gas will cost me less than the heat pump.

    During the past summer, the air conditioner was able to keep it 76 degrees F inside on all but a couple of 102+ degree days, when it got up as high as 78 degrees F inside. We've had 20 days of 100+ degrees, so the system seemed to do okay (wallet didn't do as well).

    The original owners had the Lennox Merit 51M32 thermostat balance point set to 55 degrees F. All of the stories I've read talk about setting balance point to anywhere between 15-30 degrees F.

    Can you guys figure out if I should just leave the balance point at 55 degrees, or does it need to be set lower?

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,803
    At your gas and electric rates. The heat pump is never cheaper then your gas.

    Your gas furnace cost you $5.64 per 1,000,000 BTUs of delivered heat.
    Your heat pump at a COP of 6, cost you $6.34 per 1,000,000 BTUs of delivered heat.

    The highest COP you posted is 5.09
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  3. #3
    Join Date
    Oct 2012
    Posts
    6
    Quote Originally Posted by beenthere View Post
    At your gas and electric rates. The heat pump is never cheaper then your gas.
    Thank you for the quick answer! That explains the high bp. I'll revisit the numbers if the local electric monopoly ever considers lowering the rates...

    Time to get the gas turned back on...

  4. #4
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,958
    Watch the gas prices, they tend to vary a lot. Right now gas prices are the lowest they have been in awhile.

  5. #5
    Join Date
    Oct 2012
    Posts
    6
    Quote Originally Posted by 54regcab View Post
    Watch the gas prices, they tend to vary a lot. Right now gas prices are the lowest they have been in awhile.
    You're certainly right about that. My last electric and gas bills are amazing. Even using exclusively gas for heat, the gas bill came in a $150 and electric at $250 (3 kids + electric water heater). I can't imagine how much it would have cost to run the heat pump instead of using gas heat.

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