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Heat pump/HVAC question from a plumber

55Trucker Member Posts: 20
My son bought a house in Maine a year ago that has a FHA heating system fired by oil. The furnace has an evaporator coil installed, but is currently not connected to anything. I am guessing that the previous owner had plans to add central A/C, but never did.

My question is, can this system be turned into a two-fuel system (electric and oil) providing heat and A/C) by adding a heat pump and some sort of control system? His family got badly impacted by the cost of oil last winter, and it will be worse this winter. I'm trying to figure out what I can do to help him. The house is also sitting on about 3 acres of pasture, and I wonder is geothermal could be added to this system (acknowledging that this is probably the most expensive option).

Any help from all of you experts would be greatly appreciated, especially any pointers that you can provide on how to design a more efficient solution than what he has. He lives in an area where it is pretty much impossible to get an HVAC company out there to help him. Thank you.


  • mattmia2
    mattmia2 Member Posts: 9,840
    The same coil generally can be used for AC and for a heat pump although it may not be big enough to give as much heating as you need.

    If it wasn't installed recently it may be designed for r-22 so it would be difficult to use it with a modern system. You may need a new coil which may only be 1/4 or so the cost of the whole project.
  • 55Trucker
    55Trucker Member Posts: 20
    Thank you. I will be there tomorrow, and will check for any details about the evaporator. I believe the FHA system was installed circa 2010 though.
  • bburd
    bburd Member Posts: 926
    If you can, take a picture of the rating plate on the furnace. That will tell us how much air it can deliver, therefore what size coil you can put on there.

  • Hot_water_fan
    Hot_water_fan Member Posts: 1,899
    edited September 2022
    Geothermal can economically outperform air source when you have the following:
    1. Cold climate
    2. High heat loss
    3. High gas/oil/propane costs and
    4. High electricity costs. 

    You really need all 4 however to be in the ballpark, otherwise air source heat pump + electric and/or fossil backup usually wins out. If you have the first three, often solar + air source still comes out ahead of ground source and air sealing/insulation improvements are often competitive in eliminating #2. 
  • Jamie Hall
    Jamie Hall Member Posts: 23,544
    I'd agree with @Hot_water_fan there, but with two additional comments. First, yes the running cost of the geothermal option will outperform oil -- though that does depend some on the local electric rates; where I am located (northwestern Connecticut) you need a COP from the heat pump of at least 3 to break even (even with the current eye-watering oil prices!). Second, the capital cost of a heat pump installation -- particularly ground source -- is going to be rather high, and one needs to figure the potential costs of that capital. The capital cost for ground source, however, can be reduced somewhat if one is able to install, or at least dig the trenches for, the necessary ground loops -- but that depends again on just where you are in Maine.
    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: 1,899
    The calculation for you is:
    $ per unit * 1,000,000/BTUs/unit) / COP = $/Million BTU. Using round numbers, $5/gallon oil is about $45/MMBtu. $.24/kwh works out to $23.45/MMBTU with a COP of 3. A COP = 2 gets you $35.17/MMBTU, but obviously I don't know what your fuel prices are, these are just examples. Pretty easy to see the appeal of a heat pump's contribution.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,356
    Hi @55Trucker , Do you think any significant improvements can be made in the shell of the house? Might air sealing and/or insulation be beneficial? If so, it would make heating costs, by whatever means, easier to bear.

    Yours, Larry
  • 55Trucker
    55Trucker Member Posts: 20
    The house is interesting. It is a late 1800s farmhouse, that was lifted and a concrete foundation put under it (complete with radiant heating pex in the basement floor, that is not connected to anything). Then a barn was torn down, and the timbers repurposed to build an addition (dining room, kitchen, and family room) in a structure perpendicular the farmhouse. The farmhouse and added structure are now 2x6 construction, wrapped, all very well-insulated with fiberglass and foam, with quality thermopane windows, insulated doors, and storm doors. The structure looks very well done for the climate. So I am really not concerned (by looking at it) about any severe air leak issues. When the weather gets cooler I will go through the house with my thermal camera and see where any leaks may exist and address them (wish I did this for him last winter).
  • hot_rod
    hot_rod Member Posts: 22,353
    It is always good to start with a heat load calc before you shop for components. The label on the old equipment may not match the current load 
    with a load calc and heat emitter survey you can see if air to water pencils out. Generally speaking 120F supply water temperature is what you should size to

    Radiant should work in that range, a multi pass hw coil may be needed for forced air with 120 SWT
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream