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Community and Q&A

Air source heat pumps in New England

forcedexposure | Posted in GBA Pro Help on

Hi folks,

I live in the town of Arlington, which is 8 miles from Boston, Massachusetts. My town is aiming to be Net Zero by 2050. There is currently a program running called HeatSmart, which offers discounts to home owners on renewable heating system installations from vetted installers.

I’m one of the people participating in this program and I am hoping to replace my inefficient gas steam heat system with air source heat pumps. I will also be installing a fireplace insert, after the new 2020 EPA wood stove regulations go into effect. That wood burning insert will be my backup heating system. So I think I know what I’m doing and I also have a couple of advisors assisting with this project.

However, a bunch of my neighbors who are participating in the HeatSmart program don’t know whether to switch to ASHPs or not and we are all looking for answers to the following questions:

” What is the average monthly cost during the winter?
Did they keep the home warm enough on very cold days?
How was the basement since units are not placed there?
Looking to replace oil trying to decide between these or a gas furnace.”

Note: The attached spreadsheet can be used for calculating heating costs, but I don’t know how to use it. Free strawberry rhubarb pie for anyone who can help me fill this out! 

TIA, Kristin

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  1. BillDietze | | #1

    Kristin, search this site using "minisplits" as the search term and you will get a good number of articles on the subject. Lots of good examples of minisplit heat pumps in New England, many in colder climates than yours. The issue isn't the ability to heat when it's cold, they do that quite well for boston's climate, but how well does your floor plan work with minisplit wall units vs. ducted minisplits.

    As for, your attached spread sheet, the reduction in heating costs from $3,258 with oil to $240 per year is simply suspicious. Is your electricity rate really $0.02 per KWh as stated in the sheet? That's very low. When I search the internet for Boston electricity rates, is see rates seven times higher than this. The would raise their heating cost estimate to $1,680 per year for the minisplits. That's a number I can believe.


  2. forcedexposure | | #2

    Hi Bill,

    Thanks so much for the response.

    I will research minisplits on this site, for sure, and hope to come back to my neighbors with something like:
    "Yes, we can have ASHPs as the only heating source when it's above -x degrees Fahrenheit. But it won't be as cheap as gas or oil when it gets to be below x degrees Fahrenheit out."

    As for my spreadsheet, forgive me cuz honestly I'm not quite sure how to fill it out, so the numbers there are not accurate or incomplete. I do have a Snugg Pro report from a blower door test and am trying to apply those results to this simple spreadsheet. The field that i'm stuck on filling out is the "existing system loss" number.

    I put in .02 per KWh for the cost of electricity because that's what I calculated my electricity cost to be when it is generated on my roof from solar panels.

    You are still right, of course: If I buy electricity from our local provider, it's way more expensive at approx. .19 / kWh. Whether or not I'm able to generate enough power on my roof to fuel the house and car is a question that the future will answer. Hopefully I get to 100% renewable, but I'll be happy with 70% if I don't lose money over time doing it.

    To give you an idea of what i'm dealing with: my house is a 1934 cape that poses as a poor man's tudor, with dormer windows, a gable roof, and original hand-cut cedar shingles. There's a bunch of insulation work that needs to be done in the exterior walls, attic, and kneewalls. The existing heating system is gas powered steam heat and the radiators are built into the walls, which provides an incredibly low R value of insulation. And I'm not sure what we'll do about the basement as it's a patchwork of poor "upgrades" with finished ceilings and floors.

    I've updated that spreadsheet with more accurate numbers for my scenario.

    best wishes, Kristin

  3. STEPHEN SHEEHY | | #3

    I used to live in suburban Boston. Now I'm in Maine. It's a lot colder. My cold climate Fujitsu RLS3H heat pumps work just fine at temperatures way colder than it ever gets in Arlington.

    1. forcedexposure | | #4

      Thank you, Stephen!

  4. Expert Member
    BILL WICHERS | | #5

    It would probably be a good idea to compare the heating costs for the two system
    Types using oil costs and electric utility rates, not calculated solar costs for your rooftop solar system. Doing it this way gives you more of a worst-case estimate, which is safer for planning purposes. Any additional savings from your rooftop solar installation then just becomes an extra bonus in cost savings, but not something you’re counting on to make your numbers work in the long term.


    1. forcedexposure | | #6

      Thanks for the suggestion, Bill. In my own case, I'm going from gas powered steam heat to electric ASHPs. So I'll keep the existing fuel column set at "Natural Gas". But it is sound reasoning to enter the .19 / kWh for the electrical cost.

      My new 9.45 kW solar panel array hasn't gone live, yet. The building inspector comes to see it next week and so I'm not sure yet if the estimated annual production of 7750 kWh is real. There's also a lot of air sealing and insulation work to do and we don't how much energy that will conserve. I do hope that we can save 50% of the heat generated after air sealing and insulation, but this beautiful but leaky old house is complicated.

      Still, even after changing the electric cost from .02/kWh to .19/kWh, these ASHPs look way more efficient than natural gas!

      Thanks so much for your help, folks. This site is incredibly valuable. :)

      The main question that my neighbors and I have is whether or not ASHPs can be the sole heat system in a house in Boston.'s answer is YES. That's awesome!

      best wishes, Kristin

      1. Expert Member
        Dana Dorsett | | #18

        A former coworker of mine in Arlington mothballed his oil-fired steam on a ~1700' (very cute) 1920s bungalow, squirted some cellulose in the attic and walls, put 3" of HFO blown 2lb foam on the CMU foundation basement walls (behind wallboard on steel furring) and is now heating/cooling with 3 ductless mini-splits.

        To quell uxorial anxiety the steam plant remains functional, and is even fired up occasionally when it's going to drop into the low single digits, but it's not really needed. I had different ideas as to how the upper floor should have been dealt with- it really needed/wanted to a 3/4 ton ducted Fujitsu 9RLFCD rather than a Mitsubishi FH12NA but he couldn't find the right contractor in the time frame he had. It was hard enough to squeeze out a few Mitsubishi proposals that weren't absolutely ridiculous or insane.

        I won't be sharing name & address without prior permission, but that house is on the NW side of Adams St. between Mass Ave and Andrew St. If you look closely you can probably spot the three Mitsubishi compressors on the NE side of the house peeking between the shrubbery from the sidewalk (if not the sidewalk, the neighbor's driveway.) I don't know how interested they would be in sharing utilities and other information with you or others, but it wouldn't hurt to slip a note in the mail slot with contact info and a paragraph about how much it costs to run the mini-splits.

  5. Patrick_OSullivan | | #7

    Have you double checked your cost of natural gas (i.e. price per therm, spreadsheet cell I21)? $1.56/therm may very well be correct for your location, but my last bill (in NJ) was $0.87/therm. I realize NJ might have some geographic advantages for natural gas, but it's still a big gap.

    1. forcedexposure | | #8

      Looking over my National Grid gas bills, it appears that the per therm charges vary from month to month. For instance, on the March 2019 bill, the cost (not including the minimum charge) is $1.5083 /therm. But on the May 2019 bill, the cost (not including the minimum charge) is $1.0712/therm.

      Over a one year period, I used 1249 therms. In that same period, I paid $1625.08. That calculates to $1.30/therm. I'll make the adjustment. Thanks for pointing that out, Patrick! I must've used a single (more expensive) bill to determine the cost per therm.

      The price of natural gas from National Grid fluctuates wildly, while the cost of electricity from Eversource is exceedingly more stable. Nutz

  6. Jon_R | | #9

    I suggest that you:

    1) set the equipment efficiency to 96% (typical new gas furnace)
    2) set system loss to 0% (assuming you have all interior ducts)
    3) set the utility rate to $.19

    When I do this, it says that nat gas is cheaper (but not necessarily greener).

    1. forcedexposure | | #13

      Hi Jon,

      re: the equipment efficiency
      My furnace has been tested recently and I have these numbers from the Snugg Pro report:
      Heating System Efficiency 82 AFUE

      re: the system loss
      I'm not sure what system loss is. I do not have any ductwork. I've got a steam furnace with radiators built into the walls. The radiators look very cute, but the R Value of the exterior walls that they're built into is estimated at 1 R. I will be looking at the cost of removing the radiators so that those cavities can be better insulated. I know this sounds crazy, but there is a Clean Energy Center rebate that will aid in the cost of the existing heating system removal.

      re: utility rate
      I've changed the utility rate to .19.

      Thanks! Kristin

      1. Jon_R | | #17

        Use 96% to compare a new ducted gas furnace to a heat pump and 82% to compare your existing system (let's call it a gas boiler) to a heat pump.

  7. BillDietze | | #10

    Jon, the difficulty following your calculation is that Kristen has already purchased her PV array. Now there's a penalty is she doesn't use all the electricity she generates. If kristen's hot water generation is resistive electric and her plug loads average 400 W, then that consumes the bulk of her expected 7750 kWh of production from the PV setup and your reasoning holds. But if her hot water is natural gas, or a heat pump WH with drain water heat recovery, then the minisplits will look better and might come out on top.

    1. Jon_R | | #12

      I agree. Will take some more work to come up with the right electric rate. Usage, solar production and net metering policies matter (unless one gets really fancy with water thermal storage).

      The operating cost crossover point may be about $.14/kwh. But collecting a years worth of data would help.

    2. forcedexposure | | #14

      Hi Bill,

      What is the penalty if I don't use all the electricity that the panels generate? We've got net metering in these parts and also this crazy and unbelievable thing called the Solar Massachusetts Renewable Target (Smart Money) program, where somehow I'm supposed to receive checks in the mail every month for the next ten years.

      re: my existing hot water heater specs
      Fuel: Natural Gas
      Type: Tank Water Heater
      Age: 0-5
      Location: Indoors and within heated area (*not true after I stop using the gas furnace*)
      Temperature Settings: Low (120-130 F)
      Energy Factor: 61 EF

      It's possible that I'll switch to a heat pump hot water heater as part of this project. That water heater has an annoying energy star sticker on it that reads annual estimated energy use = 254 therms and the estimated annual cost to run it is off the chart in the wrong direction. It makes me mad! lolz

      1. BillDietze | | #16

        It's not really possible for me to answer your question other than "it depends on your net metering agreement". Some net metering agreements zero out your excess production annually. Other agreements let you bank the annual excess, but if you never use it, either you don't get it back or the utility pays you cash for your kWh, but a a rate much lower than you metered rate. I live in an area where I can bank the annual excess, but if I never use it, I get paid about a third or half the meter rate for the cumulative excess. You situationation sounds quite different from mine. Check the agreement/contact for your specific program is my best advice.

        Look into the drain water heat recovery units as well. Since you have a basement, that might work well for you. They can recycle about half (or more!) of the heat while showering and reduce the energy needed to heat water by about 25% overall. Search the site for "Drain water heat recovery" for more info.


  8. STEPHEN SHEEHY | | #11

    Kristen. If your solar array is facing more or less South and isn't shaded by trees or something else, 9.45 kw should produce at least 11000 kwh annually. My 6.6kw array generates about 8,000. I'd check with the solar installer. I'd hate to see you install gas heat and generate excess solar power when you could be using your solar power for heat.

    1. forcedexposure | | #15

      hi Stephen,

      Wow, you've got a much better solar situation than me!

      My roof is not ideal for solar. It's not south facing; it has three dormer windows on one side of the roof and is broken in half with a gable on the other side. I was able to add five more LG 365s to the house by adding a Sunmodo awning over the back deck.

      And, yes, there are trees surrounding the house. The estimated power production with the trees removed is 8,923 kWh/year. But the lots are small in my town and most of the trees that are blocking the sun are in my neighbors' yards. There are a couple scrappy Norway maples that maybe my good neighbors aren't too attached to. Maybe they'll let me remove some of them.

      You have given me some hope here that maybe the production estimates are good!

      My goal is to remove the gas furnace and instead install hyper heat ductless mini splits. Then I can use the PV power to heat the house.

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