Would you choose a lower amperage Rheem heat-pump water heater?
I am considering installing a Rheem 50 gallon heat pump water heater. One consideration was the need for a new 30 amp/240 volt dedicated circuit. Today, I noticed a press release from Rheem stating it now offers the Prestige HPWH in either a 15 amp/120 volt and a 30 amp/240 volt version. I contacted Rheem to find out more about what the tradeoffs might be between the two amperages. Here is the company’s slightly edited response:
“Thank you for contacting Rheem. The 15-amp model contains 2250-watt heating element versus the 4500-watt of the 30-amp. The electric heating portion will have a reduced recovery rate and would follow the same principles as a standard electric water heater (see attached recovery rates). Bear in mind, however, that with the added heat pump doing the bulk of the work this may not make a noticeable difference. The heating elements aside, it will not effect the heat pump operation, merely the electric heat operation.”
Since I am planning to install the HPWH in an attached garage and would operate it in “eco” or “automatic” mode, I don’t see much of a penalty for going with the simpler-to-install 15 amp unit. If the heat pump developed a fault, I could limp along with the smaller heating element until it was serviced.
But maybe I am overlooking something. Thoughts?
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Replies
Can you post the recovery rate chart?
I think you'd be fine with a 2250W element, but I'm not sure how you're going to run that on a 15 amp 120 Vac circuit. Even if you max out that circuit breaker you'll only get 1800W.
Calum,
Here it is. Hopefully the new site will support PDF so posters don't have to convert images they want to upload.
I've been looking into the Rheem hybrid units and also noticed the 15A version. Nowhere did I see the mention of 120V though, and your 2250W power draw would seem to confirm that the unit works on a 15A 240V circuit. As Calum Wilde points out, 1800W is about the limit for a 120V 15A circuit.
At a 60F temp rise you're only going to get about 15-16 gal/hour from a 2250W tank. No big deal if you only have two people showering at once. The third will have to wait a while for the tank to recover. With low-flow shower heads and a Drain Water Heat Recovery unit the situation would improve.
Actually, here's the spec sheet showing 16 gal/hour rise vs. 29 for the 30A model:
http://cdn.globalimageserver.com/FetchDocument.aspx?ID=673cb60e-0940-4d67-a487-948dfcb3db8c
The heat pump only delivers 4200 BTU/hr, or the same as a 1230W water heater. Once again, it won't matter unless you need more water than the tank holds. In automatic mode it will use the heating element in situations where the heat pump alone won't cut it.
Lance Peters
As already pointed out, both the 15A and 30A versions run on 240V. So in either case, you need a dedicated 240V circuit. If you already have a 15A/240V circuit available, then maybe that's a reason to chose the 15A model. If not, the install of neither one is simpler or easier than the other.
Another important difference here may be the need to do a panel upgrade to higher current/power.
Both sizes need a double pole breaker. The extra 15A probably isn't enough to push you over the edge of needing an upgrade. I don't think the panel upgrade issue is much of a concern here.
Bill
Bill I am pretty sure the design goal of 120 Volt model is for someone to be able to remove an existing gas water heater and plug the 120V HPWH into a nearby existing outlet and avoid costly electrical work while converting.
“Quick and Easy Install/Drop-in Gas Replacement
Because it’s a quick and easy install with minimal clearance requirements and a standard tank footprint, the 120V ProTerra Plug-in is ideal for drop-in gas unit replacement and high-efficiency upgrades without the need to install a 240V electric service. They are available in dedicated and shared circuit models.”
https://www.rheem.com/water-heating/articles/rheem-proterra-plug-in-heat-pump-water-heaters-designed-for-easy-gas-unit-replacement-2/
Walta
The 2.25kW mentioned earlier would need a 30A 120V circuit, so it's more likely to be running on a 15A 240V circuit, which would require a double pole breaker.
A 120V unit would only need a single pole breaker, and would be even less of a concern in terms of potentially overloading an electrical panel.
Bill
Summarizing
It all comes down to cost.
My projects start off with a 30amp unit. But if there are amperage limitations at the service or the subpanel or whatever which would incur other expenses, then it's nice to have the 15 amp and 120V options.
Or, there is capacity now, but future electrification efforts may be affected by this current (pun) choice of HPWH unit. E.g. would a 30-amp water heater impact a future EV charger install?
For a more wholistic approach, google "Watt-Diet" from Tom Kabat.
Most residential services run at such low percent utilization on average that it doesn't usually make much difference. The most likely thing to require an upgrade would be either an electric on demand water heater or one of the really beefy EV chargers.
Bill
Totally agree, but proving NEC 220.87 is not a trivial process. My building departments typically trigger a service upgrade unless you can prove otherwise.