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Heating cost - Gas hydronic vs Heat Pump Split for addition

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Steve Garson_2
Steve Garson_2 Member Posts: 712
edited February 2023 in THE MAIN WALL
We all have read about modern heat pumps being 200% efficient. I was running some numbers comparing the cost versus gas, since we are adding a new room to our house, which is heated with a 90% efficient gas hydronic boiler.

Please tell me if my logic is correct:

Gas cost in Denver: $1.32/therm = 100,000 BTU
Electric cost in Denver: $0.143 per kwh

29.3 kwh = 100,000 BTU at 100% efficency
If heat pump is 200% efficient, that's 14.65 kwh = $2.095/100,000 BTU

Gas heating cost at 90% efficiency: $1.32 x 100,000/90,000 = $1.46

Therefore, heating with gas costs 30% less (corrected). Based on present energy costs.

Is my logic correct?

Steve
Steve from Denver, CO

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,639
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    Yes
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
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    That’s the correct calculation, right up until the end: 1-1.46/2.10 = 30% cheaper. My COP is about 3, which would make the heat pump cheaper. These prices change all the time, so don’t sweat the small differences. Does your addition want AC? That’s the real kicker. 
    Steve Garson_2
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited February 2023
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    One must factor in all costs over time, not just usage costs. Usually costs of an agenda are only expressed that make that agenda look good. Real costs are suppressed. A lot like the CPI (consumer price index).
  • pecmsg
    pecmsg Member Posts: 4,955
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    What do you have currently for heat?
    furnace, HW Radiators, Steam?
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
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    @HomerJSmith no politics on the wall please. 
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited February 2023
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    Hot_water_fan, that ain't politics that's Economics, there is a difference.
    Economics: noun
    (used with a singular verb) the science that deals with the production, distribution, and consumption of goods and services, or the material welfare of humankind.
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
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    I suppose economic agendas could be apolitical. No problem with me then. 
  • Steve Garson_2
    Steve Garson_2 Member Posts: 712
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    Using baseboard hydronic in rest of house. Was planning to do the same in new room with heat pump for AC. Then decided that I should just install the heat pump to avoid the cost of extending plumbing to the new room for baseboard.
    Steve from Denver, CO
    Hot_water_fan
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
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    @Steve Garson_2 yup that’s usually the kicker: pay about the same for heat, but get AC and save the baseboard parts and installation. For an addition, your additional annual heat cost should be low! 
  • Steamhead
    Steamhead Member Posts: 17,006
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    The HP would give you some redundancy. But I'd still do HWBB for its superior comfort as compared to the HP.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    DJD775realliveplumber
  • pecmsg
    pecmsg Member Posts: 4,955
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    Heat pumps do a good job but I still wouldn’t use them as primary heat. When it’s cold and windy you’ll want that HW Radiator. 
    DJD775
  • Jamie Hall
    Jamie Hall Member Posts: 23,639
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    Folks, we don't know where this is located. It makes a difference. In some more southern areas, a heat pump is fine for all your heating needs, with a/c as a benefit. Further south, a heat pump is fine for all your a/c, with heat as a benefit. Where I am located, a heat pump is fine for heat in the shoulder seasons, but goes paws up on a cold day when the steam takes over. A/C is needed maybe two days a year.

    So... where is this?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    pecmsg
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
    edited February 2023
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    @Jamie Hall the location is Denver, based on the original post. The OP wants AC too. 
  • Steve Garson_2
    Steve Garson_2 Member Posts: 712
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    My heat pump was fine to minus 5.  The two nights it hit minus 10 when my boiler failed, 65 was the best I could do, which actually amazed me.  Was glad for redundancy.
    Steve from Denver, CO
  • pecmsg
    pecmsg Member Posts: 4,955
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    My heat pump was fine to minus 5.  The two nights it hit minus 10 when my boiler failed, 65 was the best I could do, which actually amazed me.  Was glad for redundancy.
    Exactly!
  • Jamie Hall
    Jamie Hall Member Posts: 23,639
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    Might get away with just a heat pump then. There will be a few days each winter when it won't make it happen, but -- some folks don't mind.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,219
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    We all have read about modern heat pumps being 200% efficient. I was running some numbers comparing the cost versus gas, since we are adding a new room to our house, which is heated with a 90% efficient gas hydronic boiler.

    Please tell me if my logic is correct:

    Gas cost in Denver: $1.32/therm = 100,000 BTU
    Electric cost in Denver: $0.143 per kwh

    29.3 kwh = 100,000 BTU at 100% efficency
    If heat pump is 200% efficient, that's 14.65 kwh = $2.095/100,000 BTU

    Gas heating cost at 90% efficiency: $1.32 x 100,000/90,000 = $1.46

    Therefore, heating with gas costs 30% less (corrected). Based on present energy costs.

    Is my logic correct?

    Steve

    You left a piece out of your pricing.... Your gas boiler is also using electricity and that cost needs to be figured in. "High Efficiency" boilers tends to use large amounts of electricity compared to "standard efficiency" boilers, so your electricity usage over a heating season can add up. Being as cold as Denver is, I could see your COP being near 2 instead of 3.0 in much warmer climates. The other factor is when is Denver going to start running out of electricity in cold snaps... About 3/4 of the U.S. population is already there... as demonstrated this last Christmas. I would certainly want a back up for weather extremes going forward.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    Steve Garson_2