Heat Pump Efficiency | At What Temperature Is A Heat Pump NOT Effective?

Many homeowners who want to install a heat pump wonder: At what temperature does a heat pump stop being effective (specifically in Heating mode)?

In cooling mode, ALL heat pumps are very efficient, and work from northern Canada all the way south to Central America.

Typically, heat pumps have cooling operating temperature range of 15°F to 115°F (-10°C to 46°C). This means that if you live in ANY part of USA, a heat pump will provide adequate cooling.

When it comes to heating, some heat pumps can be limited in their ability to provide sufficient heat in extra low ambient temperatures.

Overall, (air source) heat pumps are VERY effective in terms of energy efficiency and operating ranges. What homeowners need to know is that to get efficient heating with a heat pump, they need an “inverter” type unit, which can modulate output, and provide heat when outdoor temperatures drop below 5°F. These high efficiency “inverter” heat pumps can cost significantly more than a basic 1 or 2 stage heat pumps, which are essentially over glorified central ACs.

However, before we delve into figuring out at which temperatures heat pump systems stop being efficient and effective, let’s make another differentiation:

There Are Two Types Of Air Source Heat Pumps

1) Ductless (mini-split) heat pump.
2) Central or whole-house heat pump

There are also so called PTAC or “Packaged Terminal Air Conditioners”, but these are not typically used in private residences or even commercial buildings.

PTACs are usually found in hotels/motels, where they do excellent job, but that is a topic for another article, so here we will not review them.



Average Costs For:
Most Homeowners Spent Between: Most People Spent: $8,267 - $11,796 (1750 - 2300 sq. ft.)
Low End
$7,272
Average
$9,774
High End
$16,180

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Now let’s see when and where heat pumps are and are not effective:

At What Temperature Is A DUCTLESS Heat Pump NOT effective?

There are all kinds of ductless units, which primarily offer better efficiency and quality, based on how much ductless systems cost. Four our purposes we will look at most efficient units from Fujitsu and Mitsubishi (Fujitsu 12RLS3YH & Mitsubishi MZ-FH12NAH) in 12K BTU capacity , which is enough for 400-500 sq. ft.

Both of these heat pumps come in Low Heat packages, which allow them to produce heating in -15°F (-26°C) for Fujitsu and -13°F (-25°C) for Mitsubishi. Low operating terms are pretty close.

Now the question is – are these units effective at such low temperatures?

Here is a review of my 9000 BTU (33-SEER) Fujitsu Mini Split working in Heating Mode:

As you can see, this Extra Low Heat model of has no problem heating my 600 sq. ft. loft during cold Massachusetts winter.

Best Heat Pump: Fujitsu vs Mitsubishi

Let’s look closely at specifications:

Fuji 12RLS3YH has “Nominal Heating Capacity” of 16,000 BTUs and max heat capacity of 22,100 BTUs.
Mitsu MZ-FH12NAH has “Nominal Heating Capacity” of 13,600 BTUs and max heat capacity of 21,000 BTUs.

Installing Fujitsu Ductless Heat Pump - 3-TON multi-zone 36000 BTUs

Nominal Heating Capacity usually means the rated capacity (typically at 17°F). However specs for these two units do not state “nominal” temperature. So we will use low temps:

Temp Fujitsu Mitsubishi
+5°F 22,080 BTUs 13,600 BTUs
-5°F 20,000 BTUs 11,690 BTUs
-15°F 15,680 BTUs 9,920 BTUs
Typical Cost To Install Ductless Mini-Split Average: $3,070 - $4,380
See costs in your area

As you can see from the table above, the lower are the outside temperatures, the lower is the capacity or amount of heat, which these heat pumps can provide.

However, even at the coldest limit, Fujitsu is rated at 98% of its nominal capacity, whereas Mitsubishi would only provide 73% of its rated capacity, and 37% less heating that its Fujitsu counterpart.

If you have electric (resistive) heat, you should switch to a Heat Pump NOW!

ANY brand name heat pump (Fujitsu, Mitsubishi, Daikin, LG, and many other less known brands) will have 2.5-4 times higher efficiency (also known as COP or “Coefficient of Performance”) than electric baseboards / space heaters. That means you will use 2.5 to 4 times less electricity to heat your house!

For example, if your electric bill in the winter is $600, and you get a 3 COP heat pump, you will then be paying only about $200/month. You can compare the cost and efficiency of a central air system (furnace) vs a ductless mini split (heat pump)

Now, lets answer the question whether heat pumps are EFFECTIVE in low temps. I would say YES, with some limitations.

If you regularly experience winter outdoor temps below -10°F (-23°C) then you should look at more common fossil fuel heating systems such as Gas/Oil Boiler or Furnace.

However, the majority of US households have average winter temps at or ABOVE -5°F, and thus we would recommend having a Ductless Mini-Split heat pump as a primary heating system for most US homes, with some conditions/limitations:

  • You should have a backup source of heating, such as your old(er) boiler/furnace.
  • If you have access to natural gas, a high efficiency condensing boiler will cost less to operate, compared to electric Heat Pumps.
  • If you live in any New England state (Connecticut, Massachusetts, Maine, New Hampshire, Rhode Island, Vermont), where electricity is very expensive (above $0.21/kWh) we still recommend going with a Gas Boiler or furnace, in terms of fuel costs. Here we delve deeper into comparing the pros and cons, as well as costs of a boiler vs furnace.
  • If you plan to have a large Solar PV array installed on your roof, then going with a Heat Pump is a no brainer!
  • If you live in any area in the Climate Region 1 (see map below), you should have a backup heating system for when it gets TOO cold for heat pumps to operate, or if your power goes down.

HVAC load climate zone map

Also keep in mind that as total system capacity of a ductless system goes up, its efficiency goes down. However, both Fujitsu and Mitsubishi have extra low heat models with 4 zone or more, connected to same outdoor compressor, and operate in temps as low as -13/-15°F.

Also, for larger systems (over 36K BTUs /3 Tons), Mitsubishi and also Daikin (not mentioned above) have more efficient systems than Fujitsu, and more options for 4+ zones. However Daikin does not have many models that heat in temps below -5°F. That’s why we did not include them in the comparison above.

At What Temperature is a CENTRAL (whole-house) Heat Pump NOT effective?

Central heat pumps are a whole different market, and these HVAC systems have a different purpose. They are intended to replace Central AC (air conditioners) that are low efficiency, and to provide some heating in mild temperatures, as well as “smart fuel switching” in colder temps.

Basically, as you get close to freezing temps (+32°F or 0°C), most Central Heat Pumps, stop producing heat, and switch to either Gas furnace or resistance heating element installed in place where furnace would be.

Think of the latter as an oversized space heater – very expensive to operate.

Basically, Central Heat Pumps are only effective in warmer climates (Regions 3, 4 and 5 on the Climate Region Map above).

Average Costs For:
Most Homeowners Spent Between: Most People Spent: $7,776 - $9,615 (1250 - 1750 sq. ft.)
Low End
$7,272
Average
$8,186
High End
$10,423

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About Leo B

Leo has been a contractor since 2003, specializing in: roofing, siding, general contracting (GC) and residential remodeling. Leo is also a Certified HVAC, Oil & Gas Heating Technician/Installer. In addition to roofing and remodeling, Leo is passionate about Solar, green building and energy conservation, so a lot of my time and energy goes to installing energy efficient heating and cooling systems.


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14 comments on “Heat Pump Efficiency | At What Temperature Is A Heat Pump NOT Effective?

  1. paul

    Leo, I am also in MA, south of Boston. Installers I’ve met with use Fujitsu or Mitsubishi. I am concerned with the hyper heat units having a pan heater at about 6 or 7 amps that is on constantly below 36 degrees. That would be over $100 for each unit if on for a month! I’m told the non hyper Mitsubishi units (non-ducted) do not qualify for the Mass Save rebate. The 24Kbtu Fuji does qualify but I need one a bit bigger too, 30K to 36K. (I need six indoor units) I don’t want to spend up to $200 a month for a pan heater! How can these hyper heat units be more efficient if there’s a big resistive heater going outdoors? Why have a pan at all?

    Reply
    1. Leo B Post author

      Paul – I’m also in the Boston area.

      That is pretty crazy … 6-7 AMPS would cost you a lot more than $100 a month. My calculation gives me $414 at 6 AMP (1440 Watts) @ $0.40/kWh, which is what Eversource charges me. Here is my formula:
      6A * 240V / 1000 * 24 hours * 30 days * $0.4 = $414/mo. At 7 Amps it is $483/mo.

      Perhaps you meant 6-7 Watts?

      I know 2-3 years ago, all Mitsubishi Hyper Heat models needed base pan heater to be field-installed by HVAC technician. All Fujitsu Hyper Heat units (xLTH actual name), have base pan heater installed in the factory, and it comes on automatically OR is always on … I’m not sure.

      I use/install only Fujitsu, and my idle power is about 40W for the RLS3HY (no longer produced/sold, but still top of the line) which is a lot, and its newer model replacement (LZAS series) idles at 7 watts – both are 9K hyper heat models with factory installed base pan heaters.

      The 36K BTU 4-zone hyper heat Fujitsu idles at 0 watt … I just installed it in the Summer of 2022, and it’s too warm now to run base pan heater … I will have more data later in the year, as it gets colder.

      BTW, running one 18K Zone in heating mode when it was 34F outside at night (Oct 8) used about 17 hWh for the day, and the highest load was 1.16 kWh at 1AM on oct 9th. System ran continuously for 3 days at 74F in heat mode, fan on auto, and heated space about 600 s.f., with a lot of air leaks, which I unfortunately cannot easily fix due to complex construction of the foundation.

      Now in the winter, I have them on auto running all the time, so it’s rare to idle … if you really want I will look into my historic data, but it is VERY time consuming.

      Fujitsu does not have a 30K multi-zone. Neither Mitsu or Fuji can handle 6 zones in 36K variants. Max is 4 zones. 24K Fuji is 3 zone.

      I honestly think Fujitsu is better on at least on par with Mitsubishi, and is cheaper. Fuji hyper heat models qualify for Mass Save, and if you do 6 zones 2 * 24K or 2 * 36K, that will most likely qualify as whole house, and get you $10K rebate. Contact Mass Save for details – don’t take my word.

      I think 24K is too small – not enough heating capacity for Boston winters for a whole house. I would go with 2x 36K .. I would also double check on the Mitsubishi base pan power draw … maybe call their tech support, or ask in Reddit HVAC / HVACAdvice subs. A lot of smart people there.

      If you call support, find a local Mitsubishi distributor, and ask for their tech guy’s phone number. My dealer has a guy who specializes in Fujitsu tech support.

      Good luck, Leo

      Reply
  2. Joe m

    Wow! Nice Alpine loft style setup it looks like I guess.. that roof slope is very vertical… it may work better 4U all year long @ your longitude.. I have an Ecosmart 27K electric tankless H2O & it provides adequate hot water 4 most of our needs.. cold floors are a problem.. I’ve heard Rockwool is a viable in a crawl space aside from blown foam but not with zero clearance.. that was not done with energy efficiency in mind obviously!
    Yes.. I pushed the system to BP to 25 degrees outside.. found another excellent article on how BP is determined during system sizing.. this example was in Nj no less w/a methane backup.. .. 25 degrees is about the HP lower limit on a dual energy hybrid system like I have.. @ least in region 3.
    The hvac service guy isn’t considering my electric cost as nearly zero.. he’s thinking I pay what he does.. 18 cents per kilo fish…
    I guess with the higher BTU output of methane.. he figures the methane system will reach temperature faster.. & this run less time saving energy.. not sure if I’d agree since my energy cost for electric is locked.. except below 25.. well see when it gets colder right? My vehicle tends the use more electric during the winter. & I ‘m less enthusiastic about bearing the cold just to make a supercharger trip.. so I home charge a decidedly more in the winter.. will update when it gets frigid.. hopefully get cold enough to kill off the termites.. 4 or 5 below zero a couple of nights.. I hear the formosan are the worst ever..

    Reply
  3. Joe m

    Congratulations on the solar!

    75 is too toasty 4me! My home is fairly tight.. we’d roast @ night w/that temp dialed in.. is that because the air discharge is @ the ceiling?

    My on the floor space heater is set @ 70 & my wall temp says 71 @ 5ft on the over night in our 2 2nd floor use rooms.. I’m a retiree living on a ‘broken income’…about 65% of my hours are @ home +/- depending on the outdoor weather.. less if nice.. more if not nice.

    I’ll test 30 & see how that goes for comfort . I don’t think the service guy ( though a regular pro) took into account my home electric generation capabilities.. & he just gave me the ‘standard’ answer ..

    I’d definitely like 2 use MUCH less methane.. thoroughly loath the stuff as a ‘ necessary evil but I can’t make it like I can electric.

    1 note on that electric credit.. Unless you have room & can go ground mount & be able to clean snow & ice from your panels.. once the snow & ice can & will build in winter on the panels.. production is zero for days.. maybe longer w/o a sunny day 2help melt ..even a week loss ìs possible.. that buffer can go fast when you’re not making it.. & battery back up only lasts a day or 2 w/o new production..

    Thanks 4the reply.. just looking for more knowledge & your article is very much informative. Good luck w/the approvals

    I’ll go2 30 & see what happens.. 71 from 35 is certainly seems no challenge @ all for the Lennox 2 stage HP ..just didn’t wanna be backward smart.. end up wasting more energy just trying to save some!

    Reply
    1. Leo B Post author

      Joe,

      Not only air discharge is at 6 ft above the floor, my bedroom a 2 storey loft addition, so much of the heat actually rises to the 2nd, while our bed is downstairs (see photos). On top of that, we have very cold “crawl-type foundation” directly under the bedroom, and there is no access to insulate … floors are very cold in the winter, which is very annoying. So we need to keep it warmer that usually.

      2 storey loft

      Heat Pump on first floor

      I got a feeling that your installer is not well versed in heat pumps and solar, and it did sound like a standard answer.

      As for solar being covered in snow/ice – my roof is 52° steep (14 pitch) … so most of the snow will slide off. Roof eave is 3 feet above ground, so I can easily clean it…

      I would put more solar, because I want 100% electric heating / cooling, and completely offset by solar. Unfortunately in MA net metering is capped at 10KW inverter size, and if you go over 10K, you only get 60% credit for the whole amount of electricity that you produce.

      I will put a separate (off-grid + battery backup) DIY array, but that will be primarily for my “shed-office”, and will be just 4KW + two 3000w GroWatt inverters with built-in charge controllers. In split phase these puppies can put out 240V, which can be connected to another heat pump!

      BTW – that heat pump is a mere 9000 cooling BTU Fujitsu , albeit it provides up to 22000 BTUs of heating, and can easily keep warm our 600 sq. ft. loft even when it’s -10°F outside!

      Good luck with your experiments – let me know how it goes.

      Reply
  4. Joe M

    I have 11.01 k of solar.. heat & cool my 2 story home with a Lennox 21 whole home heat pump & a back up 98% lennox methane system in southern Nj…the service installer guy who i trust told me the heat pump can never match the 98% methane.. set the BP @ 45 after the service visit … & rolled…. the Lennox rep I called later to further query stated my heat pump would make heat down to 5 degrees F.. so I went into installer settings & found & lowered my BP & now have my BP set @ 35 F .. but should I go even lower still? I keep the home @ 66 @ night using space heaters in the 2 rooms we use overnight… I note the pump does take a while longer than the methane furnace to return the home to 71 in the morning.. . I currently have a kwh credit of 2400 kilo-fish harvested beyond my to date grid use and can use that electric credit up till April of 22 ..

    Lower it to 30 ?? Or not??

    Reply
    1. Leo B Post author

      Joe, it is true that Lennox central heat pump is not as efficient as say Fujitsu or Mitsubishi mini-split heat pump, and is not as efficient as 98% gas furnace. Still, if you have solar, and 2400 kWh credit, use heat pump as much as you can. If it can heat it as low as +5F, set it to something like 15-20F lower limit … I’m not an expert on setting up Lennox, so contact their customer service, for how to setup your system.

      As for me – I like it warm – so I set my heat pump to 75F overnight, and 69F during the day, if I’m home. I have mini-splits in every room, so I only turn on zones in rooms where I am. All un-occupied zones are always off.

      My heat pump is “extra low heat” and works in -15F … and I also just got 15KW of solar… installation is almost complete, and waiting for inspections and final go from utility.

      Reply
  5. Jack

    Thank you for your tips on how to consider your backup systems when installing heat pumps. I’ve heard a lot about these kinds of appliances from other people, and I wanted to know how my own house could benefit from it. After reading your article, I’ll make sure I get an HVAC expert to help us out with installations just in case we may need to make a few adjustments.

    Reply
  6. Hugh Willis

    From an operating cost perspective, for most Americans, heat pumps already outperform gas furnaces. And as electricity gets more and more “green” sourced, Heat Pumps will be an increasingly important part of humanity’s effort to deal with CO2 emissions and other greenhouse gases.

    I ​couldn’t disagree more strongly with your statement, “… as you get close to freezing temps (+32°F or 0°C), most Central Heat Pumps stop producing heat …” You are simply wrong!

    Goodman’s specs show my 16 SEER air-source central heat pump is rated to work down to well below zero (F), and even at zero still has a CoP of 2.0. At local prices for electricity vs natural gas here in NC, the cost per therm of heat delivered into my house is about equal at 10 degrees (F) via either my 96% efficient furnace or my 16 SEER Goodman HP. (If you would like to see the computations, I’d be happy to share them).
    Although I have a “dual fuel” setup, my furnace hasn’t run for three years!
    Don’t take my word for it – see what Daiken has to say – “Do Heat Pumps Work in Atlantic Canada?”

    https://daikinatlantic.ca/2018/07/27/do-heat-pumps-work-in-atlantic-canada/#:~:text=However%2C%20problems%20occur%20when%20it%20becomes%20too%20cold,know%2C%20it%20Atlantic%20Canada%20can%20get%20quite%20cold.

    See also Manitoba,CA’s “Arctic Heat Pumps”, which work below -20 degrees
    https://www.arcticheatpumps.com/cold-climate-heat-pump-overview.htm

    Reply
    1. Leo B Post author

      I partially agree on operating costs. For example, electric costs in Chicago, IL are around $0.13/kWh, which is pretty good, while Natural Gas is about $2.24/therm – so there, Heat Pumps are way more cost-effective than say in Boston, where electricity is $0.24 (75% more expensive than in Chicago), while Gas is $1.77/therm, which is like 30% less. And here, Gas is still more cost-efficient.

      However, if you have solar, which will produce endless electricity, then Heat Pumps are a no-brainer.

      PS – to compare heating costs in different locations, for Gas, Propane, Oil and Electricity, and for different heating systems check out our Heating Costs calculator

      Reply
  7. Richard L Johnson

    Just a few data points for you. We moved into our new 2700ft2 Anacortes, WA (Zone 3) home in Mid-January 2021. We have a Daikin whole house heat pump with electric booster coils. We have gas stove, On-demand HW, and dryer. Our highest monthly electric bill to date is less than $150, gas less than $25. Our J/F/M temps average around 40 at night and 50s during the day. We also had a June heat wave with temps near 100, and we sailed through that with normal indoor temps. Our house faces West with 30 feet of 10ft high glass so heat gain and loss is definitely an issue. Very impressed with our HVAC on all aspects.

    Reply
    1. Leo B Post author

      Hey Richard,

      Yea Daikin is pretty good. I’m surprised though that with gas in the house you have electric heater coil. However 40-50°F average winter temp, you probably don’t need a furnace … its warm enough where Heat Pump can handle the load most of the time.

      I envy those temps. Here in Massachusetts, we get days of -10°F … and my ductless heat pumps handle it pretty well. But my electric bill is nowhere near $150/mo. We have some of the most expensive electricity in the nation at $0.24/kWh, while average in WA is $0.1013/kWh … so here you would be paying closer to $400/mo for same usage

      Cheers

      Reply