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I have Carrier 38MURAQ36AA3 heat pump paired with 40MUAAQ36XA3 air handler. Each unit is in its own 240V circuit; 30A and 20A respectively. I'm in Sunnyvale, CA.

What's the load of my HVAC system? I'm trying to do a load calculation to see if I can install a heat pump water heater and EVSE (asking this separately in Electrical load calculation to see if I can install heat pump water heater and EVSE).

Heat pump says 208/230V 19.0A so 230*19=4370W?

Air handler says 208/230V 4.0A so 230*4=920W?

So the load is 100% of 5290W?

But based on common values in a nice spreadsheet I found in my neighbor city Palo Alto, the electric load of a 3T heat pump like mine should be 4000W.

heat pump label without sn air handler label without sn

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  • You need to include the phase angle in your power calculation - what you have holds true for resistive loads, but not inductive loads like motors. Why not get a load meter?
    – Solar Mike
    May 25, 2023 at 7:28
  • My calculations are based on ecmag.com/magazine/articles/article-detail/… I don't have a load meter and I'm not sure it would allow me to measure the max draw.
    – user162793
    May 25, 2023 at 7:49
  • Have you confirmed that you do not have a heat kit installed in your air handler? May 25, 2023 at 11:45
  • Probably not if he's in Sunnyvale.
    – SteveSh
    May 25, 2023 at 11:53
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    Right. I don't have a heat kit installed.
    – user162793
    May 25, 2023 at 13:20

1 Answer 1

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To be safe, and allow for realistic starting loads, just take the "Minimum circuit ampacity" values from each device. That will be more than the typical running load, but represents the manufacturer's selection of how much it actually needs in the worst case.

Note that having a 20A breaker on the air handler is in violation of the manufacturer's "Max Fuse" of 15A for that device, (unless it has a fused disconnect fused at 15A or lower) so you should change that breaker to a 15 (or even a 10, since it only needs 5.)

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  • Using the minimum circuit ampacity makes sense but that would increase the load even further from the common value the spreadsheet has. These units are supposed to be one of the more efficient ones so I was expecting to be lower than the common value. I also noticed the violation while posting this question. I need to look into that.
    – user162793
    May 25, 2023 at 13:29
  • Actually I don't think I should use the minimum circuit ampacity. I think that refers to the breaker. Notice 19A/24A=80% which matches the percentage of the overall amperage the circuit breakers can handle.
    – user162793
    May 27, 2023 at 2:40

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