We are considering to install a heat-pump for heating and cooling and would like to get a better idea about any required upgrades to our electrical panel and house service. Below are pictures of our main and sub panel with labels. Our main panel currently is 100A but the panel is already wired for 120A (and the panel supports it as well). It is connected to the house service, which is 200AMP.

The condo is 1300 square feet with 2 bedroom, 1 bath. It is part of a three unit building with 200AMP service. The other two units have 100AMP panels.

Our major appliances include an electrical oven (3100W), washing machine (1300W), heat-pump dryer (1000W), dishwasher (1200W), and garbage disposal (720 W). We plan to install an induction cooktop soon (9600W).

Current heating is a gas furnace. For cooling, we have 2 window ACs.


Would our current electrical service with the easy 120A upgrade allow us to install an air source heat pump for heating and cooling with 32k or 36k BTU?

Below is load calculation from this website recommended in an answer to another stack exchange question. That calculation would suggest yes but I am not sure about the numbers.

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  • You should have entered custom wattages for your actual appliances in the online calculator…. and I should point out that technically that’s not quite the NEC / CEC load calc but it’s a a conservative approximation. Commented Feb 25, 2022 at 2:34
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    In the US, "apartment" means it's a rental. In a rental, you shouldn't be making updates like this. I'd imagine that in other countries, you probably shouldn't make updates like this to a rental, either. Can you please clarify the use of the word "apartment". Do you actually own and have permission to make changes like this?
    – FreeMan
    Commented Feb 25, 2022 at 13:38
  • Thanks @FreeMan. I am not a native speaker and was not aware that apartment = rental. The unit is a condo. I edited the question with more details on that. Commented Feb 25, 2022 at 18:37
  • Many heat pumps have “emergency heat mode” this is when the temps get cold we would need the amount of electric heat in that case because this is a major draw on the electrical system, and even the easy bump to 120a may not be enough.
    – Ed Beal
    Commented Feb 25, 2022 at 20:44
  • We don't have a unit yet but I think it will require either a 40A or a 50A breaker with 230 voltage (depending on whether the unit is 30k or 36k BTU). Commented Feb 26, 2022 at 1:57

1 Answer 1


Yes, 1300 sq ft is quite small for a 120A service with a gas furnace. Houses of this size, with gas heating, have historically been fine with a 60A service.

  • Also the other calculator I forgot to mention is here: douglashelmer.com/calculators/electrical/residential-service/… but keep in mind the CEC and NEC load calculation might be different. Commented Feb 25, 2022 at 3:02
  • It's your answer, feel free to edit that in, instead of making a comment which might get deleted at random.
    – FreeMan
    Commented Feb 25, 2022 at 13:37
  • 100 amp is the minimum sized service for a single family dwelling this has been code for many years no matter if gas or not NEC 230.79.C
    – Ed Beal
    Commented Feb 25, 2022 at 17:17
  • @EdBeal I said historically… I know plenty of people with homes that were built between 1900 and 1950 that still have 60A service. Commented Feb 25, 2022 at 17:19
  • 1950 was prior to heat pumps and on demand electric water heaters and AC for residential . with a heat pump being considered and the appliances being electric not gas if the system they choose requires emergency heat the panel looks a bit undersized. But we don’t have all the facts and this is a question and answer.
    – Ed Beal
    Commented Feb 25, 2022 at 17:35

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