Heat-pump water heater for an all-electric garage apartment?
We our building a detached garage w/ 2nd story apartment (1 bedroom, ~900 sq ft conditioned space) & debating the system to heat water:
– Primary purpose for the garage apartment is for our mothers to live in as they age. Mainly for safety reasons, we’re not having gas service to the apartment (could do relatively easily – main house has gas service)
– Cooling-dominated climate (Houston TX)
– HVAC: When we installed a ground-source heat pump for the main house several years ago, we pre-drilled 2 extra wells for the garage. I wouldn’t do a GSHP ever again, however the wells are sunk costs…since we have them, might as well use them.
– Apartment won’t be occupied all of the time (mothers may go elsewhere for Houston summers; we’re assuming 50% occupancy). If we have a tank water heater, we’d turn it off when not occupied.
– To help keep garage tolerable in summer, all garage walls will be well-insulated (2 x 6″ w/ spray foam + 3/4″ exterior rigid foam) w/ insulated garage door
I like the idea of Heat Pump Water Heaters (https://www.greenbuildingadvisor.com/blogs/dept/musings/heat-pump-water-heaters-come-age):
– System would go in the garage
– Good fit for our climate (additional cooling in the garage is desired almost year round…mid 80s in early February)
– Models seem to be ~2x as efficient as electric resistance units
– Noise isn’t an issue (condensate drain can be included in design
1. Upfront cost are higher (how much higher?)
2. Reliability unclear (most of the posts I’ve seen are 2+ years old…has reliability improved?)
3. If system isn’t used 6 months of the year, how much energy will we really save?
If we didn’t do a heat pump water heater, what’s the next best option? Tankless electric? Tank electric tied into our GSHP with a desuperheater? Something else?
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