I'm thinking of getting a heat pump hybrid water heater (this one maybe); The operating conditions will be technically within the prescribed range but less than optimal.

I'm wondering how I should expect the heater to perform (power consumption and heating performance) under these conditions. I would be interested in the "with ducting" and "without ducting" answers.

This water heater would be in a small room that can get down to around 40 deg F in the winter. The room is probably about 300 cubic feet but with an open doorway leading out into a hallway and into a larger room from there. The ceiling is probably about 7 feet.

Also, in a worst-case scenario, would it eventually be able to heat my tank just using the electric backup?

  • 2
    Did you forget to include a link to the specific model you're considering?
    – jwh20
    Sep 30, 2020 at 18:01
  • Oops! Yes, you're right.
    – capet
    Sep 30, 2020 at 18:06

1 Answer 1


For your “with ducting”, it should not be an issue at all, since you have met the full requirements with ducting.

For your “Without ducting”, in general you have met the condition, as the 300 cf room has an opening to a larger space, which meets the requirement.

In your “worst-case” scenario, it would perform just like a normal electric hot water heater with the same performance characteristics.

I have a hybrid which I installed several months ago in a true “worst-case” scenario. It is installed in a small utility closet, 4x3, which is in the laundry room, 8x10. I just leave the door open. I leave the WH locked in the heat pump mode, as I see no reason to rush to heat the water in the tank back to full capacity. If I have guests or for some other high demand days, I could manually switch it to hybrid or high demand for those occasions.

  • Thanks again @Programmer66! I will mark this as the answer tomorrow. Your discussion of the worst case mostly covers my question about operating at low temperature, but do you have any thoughts on how the heat pump component would perform around 40 deg F?
    – capet
    Sep 30, 2020 at 23:14
  • 1
    Down to 40 degrees is within the range of hybrid WH for efficiency. The hybrid can operate down to 30 degree with less efficiency. Below 40, you can switch over to hybrid mode. Oct 3, 2020 at 16:58

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