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Sizing heat pump to replace electric baseboard heat.

woobagoobaa | Posted in General Questions on

Greetings.  Situation is 1500 sq ft apartment in a multi unit building in Zone 5 (coastal).  Not well air sealed or insulated.  Electric baseboard heat with aging roof mounted AC condenser (ducted air handler within the apartment).  Recent storm tore multiple apartment’s condensers off the roof, so AC needs to be replaced.  The plan is to replace the AC with a cold climate rated heat pump.

Previous AC was a 2 ton unit.  I don’t recall any issues with cooling.  Most other unit owners of similar footage went back to a 2 ton AC offered by the insurance company.  We will pay to upgrade to a cold climate heat pump.  I have experience with Mitsubishi H2I so that is my benchmark.

The leading bids I have for this job are for a 2 ton LG …!/product/33644/7/25000///0

And a 3 ton Fujitsu …!/product/63191/7/25000///0


– will the LG be able to provide adequate heat for this place?  The intention is to only use the remaining electric baseboard for dire emergencies. 

– I am not understanding the min and max BTU/hr versus the rated capacity (for heat modes at 47, 17, and 5 degree outside temp).  Hoping someone can translate into layman’s language. 

Thank you

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  1. paul_wiedefeld | | #1

    Try this and let us know what you find!

    Use a spring or fall month with low cooling/heat usage as the baseline. We can’t answer your first question otherwise.

    The outputs to care about are only the max output at the lowest temp you’ll experience (so 5 or lower) and the min output at 47. You could compare it to a stove - the smallest burner for simmering is the 47 minimum rating and the largest burner for boiling is the 5 degree max rating.

    1. woobagoobaa | | #2

      Helpful stove analogy thanks.
      I don't have reliable electric heating bills from past few years as exterior walls have been open for water damage repairs etc. Is there a way I can take a SWAG at approximate heat loss for this 1500 sq ft? Design temp is 10 degrees.

      1. paul_wiedefeld | | #3

        How about determining the amount of existing electric baseboard? The LG is equivalent to roughly 8kw of baseboard and the Fujitsu is around 12kw, which is about 32 and 48 linear feet of 240V baseboard, respectively. This can establish a ceiling for us: if you had only 7kw of baseboard installed, the larger HP would clearly be oversized.

        Even if if the smaller unit is too small, you have existing backup so undersizing would probably be just fine - very little of the winter is spent near design temps.

        I’d try the fuel usage method anyway - you still might end up under the 2-ton unit.

        1. woobagoobaa | | #4

          I will ask my GC to measure the existing eBaseboard.

          1. Cafferatak2 | | #6

            My 48" baseboard is rated at 1000W and my 38" baseboard is rated to 750W, at 240V. If that frame of reference helps to determine what your installed capacity is.

    2. Cafferatak2 | | #5

      I get the approach Dana uses in that ariticle, it makes total sense. Did he develop it himself, or is it from a standard or manual somewhere?
      I need to convince my city government to accept it, would help if I had an original source.

  2. woobagoobaa | | #7

    The rooms with duct work have 32 linear feet of eBaseboard (2 baths and kitchen have electric kicks). LG contractor is confident heat load for entire 1500 sq ft unit is 24.5K BTU/hr at design temp. I'm leaning towards the LG. Another factor here is the additional height/windage of the higher capacity Fujitsu. I don't want it acting like a sail when the wind comes up (it would by far be the tallest unit in the condenser clusters on the roof).

    1. paul_wiedefeld | | #8


    2. Expert Member
      Akos | | #9

      With a condo with few exterior walls, with low insulation even 24.5k seems on the high side for 1500sqft.

      I would run through the calcs in the link Paul sent earlier. Although walls were open, it would still put a ceiling on your heat loss.

      Even assuming 24.5k is correct, if you are keeping some of the baseboard I think the 18k hyper heat unit would be a better fit:!/product/33580/7/25000///0

      This still produces over 2 tons of cooling in the summer in case that is your worry.

      1. paul_wiedefeld | | #10

        I like the 18k unit for the lower cooling minimum output at 82F.

  3. woobagoobaa | | #11

    My first choice of the LGRED won't make a summer work shutdown deadline. Over to contractor #2 who says he can have install done in a couple weeks and is pitching these systems ...

    Bosch IDS 2.0 ...!/product/66146/7/25000///0
    Fujitsu ...!/product/33398/7/25000///0

    I'm leaning towards the Bosch as it is substantially shorter for an exposed 4 story roof location and has slightly higher heat output at low temp.

    Can anyone contrast Bosch versus Fuji re: longer term reliability and parts availability?

    Thanks much

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