Heat pump water heater install — what I got wrong the first time and what I'd do differently
By SolarSarah·4 replies·597 views
Installed a Rheem ProTerra 50-gallon HPWH in my garage last spring. Took about 4 hours of actual work spread over two weekends (one to run the circuit, one for the physical install). It's been running 10 months and I have enough data to write an honest account.
What worked
The performance numbers are real. My water heating went from $28/month on gas to about $9/month on electricity at my PG&E rate — roughly $228/year in savings. COP in my mild Bay Area garage averages around 3.6 per the unit's monitoring app. The hot water recovery time is slower than a gas water heater but perfectly acceptable for a two-person household. The unit is noticeably quieter than I expected — about the volume of a window AC unit.
What I got wrong
First mistake: I didn't account for the cooling effect on the garage. The HPWH pulls heat from the surrounding air to heat the water, which is great in summer (free AC in the garage, essentially) but in winter it actively cools the space it's in. My garage isn't insulated and in January I noticed the unit was running its resistance backup element significantly more often than I expected, killing the COP. If I were doing it again I'd insulate the garage walls around the unit or build a small partition to isolate the unit from the adjacent crawl space where cold air infiltrates.
Second mistake: condensate drain location. I roughed in a drain line that drops into a floor drain six feet away. In summer when the unit is running the heat pump mode heavily, it produces a surprising amount of condensate — more than I expected. The drain line has a slight uphill run over about 18 inches and it occasionally backs up. A condensate pump ($35) would have avoided this. Install one regardless of your drain geometry.
Third mistake: I didn't enable demand response enrollment in the app. PG&E has a program that pays you to allow them to briefly defer the heating cycle during grid peak events. You get a bill credit, the unit smooths out its demand naturally, and you never notice the difference. Sign up for it if your utility offers it.
The $300 federal tax credit (25C) is real and easy
The Rheem ProTerra qualifies for the $300 Section 25C energy efficiency credit. Keep your receipt and the ENERGY STAR certification number. Claim it on Form 5695 Part II. If you're also doing a heat pump for space heating this year, you can stack these credits up to the $1,200 annual cap. If your state has an additional rebate (California has the TECH Clean California rebate, up to $1,000 for qualifying households), coordinate the state rebate with your contractor — the state rebate often requires licensed installation even if the federal credit doesn't.
The cooling effect issue is real and I made the same mistake. Installed mine in an uninsulated utility room in Denver. December COP dropped to about 1.8 according to my monitoring, which still beats a gas water heater economically but kills the environmental case in cold months. I added a 3" foam board to the exterior wall behind the unit and it helped noticeably — the compressor runs less and the resistance element almost never kicks in now down to about 25°F outside.
What's the minimum clearance around the unit in practice? The spec sheet for the ProTerra says 700 cubic feet of surrounding air volume. My water heater closet is roughly 4x4x8 — that's 128 cubic feet. I have a door to an adjacent garage. Does an open door to a connected space count?
@PacketDriver Yes, connected air space counts if the door is open or louvered. My plumber said a louvered door to a garage counts the garage volume toward the 700 cubic feet minimum. Some installers put a duct kit on the unit (draws air from outside or an adjacent space through a short duct) for genuinely tight closets — Rheem sells a duct kit for the ProTerra for around $80. Worth asking your installer about rather than guessing on the volume.
The condensate pump note is well taken. I'd add: route the discharge line to a utility sink, floor drain, or exterior — not into the AC condensate line. I've seen installs where someone combined the HPWH condensate with the AC line and overwhelmed it during peak summer demand. Keep them separate, install a condensate pump if there's any question about drain slope, and you'll never have a problem.