Is a heat-pump water heater in Zone 7 worth it?
![](https://secure.gravatar.com/avatar/9a12eaedd5b0a0aba778b9fbcc301875?s=52&d=https%3A%2F%2Fimages.greenbuildingadvisor.com%2Fapp%2Favatars%2F200x200%2Fm.png&r=g)
I’m currently designing a highly efficient 2 bedroom 1080 sqft house. Right now I am wondering if a heat pump water heater would pay itself off before it needs to be replaced. Also, the mechanical room would only be 3’6″ x 7’6″, not big enough size for manufactures recommendations of 10’x10’x10′
My question is how could I run the numbers to see if buying one is a good investment?
Why aren’t there any systems that have an outdoor unit and an indoor unit like HVAC air-source heat pumps? HVAC systems maintain a COP of 2.0 even during -5*F weather? Would the COP of a water heating system be less than 1.0 during winter months due to the delta-T in-comparison to an HVAC system? Say from -15*F to 70*F = 85*F delta-T for the HVAC system and -15*F to 120*F = 135*F delta-T for the water heating system?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb1.png)
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb2.png)
Replies
Matt,
The limiting factor in your case is the size of the mechanical room. It's too small, so I would eliminate a conventional heat-pump water heater from your wish list.
If you decided to make your house and your mechanical room a little bigger, you would probably find that the incremental cost of the heat-pump water heater was a good investment, but the answer depends on how much hot water your family uses (large volume users see a faster payback) and your local electric rates (payback is faster in areas where electricity is expensive).
If you want to purchase a split-system heat-pump water heater, you probably can. Here is a link to an article about the Sanden heat pump water heater: Split-System Heat-Pump Water Heaters. It's not a cheap product, however -- the cost is about $3,700, so expect the payback period to be very long.