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Community and Q&A

Cost-Effectiveness of a Heat Pump

bene0404x | Posted in Green Building Techniques on

I have a new house in progress with three “air” systems (a, b, c) and four heating systems (A, B, C, D).

(A) The main “heating only” system includes four in-floor zones and one Electro Industries Midsize Boiler Model EB-MX-15.

(B) There is a traditional furnace with ducts going to and coming from all rooms with a 1.5 KW plenum heater.

(C) is an optional Heat Pump.

(D) Also planned is a propane heating stove which fulfills the dual-fuel requirement for cheaper electricity for space heating.

(C and D) are not yet installed.

(a) One “air only” system includes three bathroom exhaust fans, one range hood exhaust fan and one make-up air flex duct open to the outside.

(b) Another “air only” system includes a down-drafting ceiling fan over the stairs and (when a laundry cabinet is open) an up-drafting laundry chute in the bathroom at the other end of the house.

(c) A third air system includes the HRV which shares some of the duct work for (B).

(a) and (c) introduce fresh outside air into the structure.

My questions:

(1) Would it be cost effective (via reduced heating cost) to install (C) which would interface with (B) via the “A coil”?

(2) How would I estimate how long it would take for (C) to repay for its installation in reduced heating cost?

Thank you for your interest.

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  1. paul_wiedefeld | | #1

    What is the furnace’s fuel? And how much does that fuel cost? And how much does electricity cost? What’s the location?
    Save some dirt cheap hydroelectric rates, (A) is likely the most expensive heating source by far unless (B) is an electric furnace, in which case they’re tied for most expensive. If you go with (C) (the best option in my opinion), I would skip B entirely. C will be about 1/3rd the fuel cost of A.

    What is the heat loss here? That boiler (51k btu) seems outrageous for a new house if you only have 4 zones (radiant floor loops are usually ~300 ft each, how many loops per zone?).

    Frankly, I’d do C and skip the rest. Maybe a gas furnace heat pump hybrid if needed.

    1. user-7519488 | | #3

      Add'l info on heating & air systems...

      Thanks, Paul:

      (i) The furnace (fan and plenum heater) is electric on the first floor.
      (ii) The house is in Northern Minnesota where winters can get down to -40 degF.
      (iii) The house is well insulated (ICF construction) and triple-pane windows.
      (iiii) On each floor: One zone has one loop; one zone has two loops. Footprint is ~1000 sq. ft.

      1. paul_wiedefeld | | #6

        Gotcha - in this case I'd go with a cold climate heat pump (ducted). If I'm understanding correctly, you have two floors, 3 loops per floor, 1000 sqft/floor and about 2000 sqft total?

        Using Grand Rapids as a stand-in, we can guess (emphasis on guess) your energy consumption based on some heat losses. Bottom line, use the heat pump as much as you can, but keep the electric resistance/propane for the days below -15.

        Why the stove vs. a furnace or a boiler? It'll be easier to distribute the heat using the loops or ducts.

  2. walta100 | | #2

    “Also planned is a propane heating stove which fulfills the dual-fuel requirement for cheaper electricity for space heating.”
    I had not seen this type of rate plan before how sure are you that you understanding are correct?

    In general a heat pump will deliver 4 BTUs of heat for the cost of 1 BTU of restive heat the colder it is outdoors the less efficiency heat pumps become but hyper heat models will work at -20°f


    1. user-7519488 | | #4

      Add'l info on heating & air systems...

      Thanks, Walt:

      Yes, I am sure about the dual-fuel rate plan (less than $0.05 per KWH vs ~$0.11 for the normal rate).

      My idea is to use a heat pump for its full range of temperatures until it gets too cold, then let the boiler do its thing.

      I have been keeping a daily log of KWHs used for each separately measured component: General (includes a house and an uninsulated cottage in temporary use) 5 - 192 KWH per day); Dual-Fuel (0 - 120 KWH per day); Off-Peak HWH (0 - 11.36 KWH per day).

      Thank you gentlemen for your interest:-)

      1. paul_wiedefeld | | #5

        I have seen the dual fuel requirement elsewhere: it's an interesting approach by the utilities because it seems much cheaper/cleaner than a peaker plant. Is this propane heated internet connected? The other plan I saw required that the utility be able to control the heater for peak loads, similar to many utilities control of air conditioners.

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