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Persuade me - Hybrid Electric Water Heater.

Big Dog

Active Member
Mar 7, 2016
1,666
1,805
Irvine, CA
Just do it. The current Rheem HPWHs are great. Putting a new gas water heater in means another 8-15 years of another gas appliance, and we need to get off fossil fuels as fast as possible.

Except the OP lives in LA, and LAWP generates 62% of its electricity from fossil fuels. So swapping to HPWC helps some...
 

Dave EV

Active Member
Jun 23, 2009
1,921
1,615
San Diego
Except the OP lives in LA, and LAWP generates 62% of its electricity from fossil fuels. So swapping to HPWC helps some...
Yes, helps some today, helps more tomorrow. Nearly all new grid resources come from solar/wind/batteries these days so the grid is getting cleaner every day and the OP also has solar, so any energy their water heater uses while the sun is up will likely be directly self-consumed.
 
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tomuo

Member
Mar 15, 2021
49
17
Los Angeles, CA
Except the OP lives in LA, and LAWP generates 62% of its electricity from fossil fuels. So swapping to HPWC helps some...
Interesting daily charts for california as a whole:

looking at the net demand for example yesterday (net = total usage minus solar/wind),
at the best time around 10am, it was 44% solar/wind
at the worst time around 8pm (least solar, most AC demand), it was at 13% solar/wind.

SCE specifically notes that hydro power is not currently included in these renewable numbers, and accounts for about 20%.

There's also some sneaky business going on in the renewable target calculations.
target for 2017-2020 was 33% renewables, which was met at 52%, and 2021 -2024 is target 60%, but any one who moves their generation to a CCA gets excluded from the calculations, only people who remain on the IOU directly count towards the amount of load that they have to meet with renewables.
 

David.85D

Active Member
Oct 29, 2016
1,513
1,281
USA
I have the Rheem HPWH. I’m very happy with it. It’s been very reliable and the internet features mostly work (drops the connection periodically for unknown reasons).

I wanted to make two suggestions. 1). Increase the storage size from what you have (we went 50 —> 80) so it can stay in HP mode most of the time. They are well insulted so the stand by losses are small.
2) remember the “waste” is a flow of cold, dry air. If you would normally be air conditioning or dehumidying, run a duct and use the “waste” from the HPWH and eliminate another appliance. That makes it very economical…. I use mine to cool a wine cellar 😎.
 

darhall993

Member
Jan 24, 2019
161
148
Sandy Springs, GA
I have the Rheem HPWH. I’m very happy with it. It’s been very reliable and the internet features mostly work (drops the connection periodically for unknown reasons).

I wanted to make two suggestions. 1). Increase the storage size from what you have (we went 50 —> 80) so it can stay in HP mode most of the time. They are well insulted so the stand by losses are small.
2) remember the “waste” is a flow of cold, dry air. If you would normally be air conditioning or dehumidying, run a duct and use the “waste” from the HPWH and eliminate another appliance. That makes it very economical…. I use mine to cool a wine cellar 😎.
Agree on all points above, great units, the wi-fi does drop periodically and won’t recover without cycling the power, I have all of mine hooked up to seperate GE zwave controlled 40 amp switches so I can remotely power cycle them. Several of my units are in rental units and one vacation home
 

David.85D

Active Member
Oct 29, 2016
1,513
1,281
USA
to whom ever asked about the 20A service. It’s a bit irritating really. I believe it’s rated to 18A (230VAC) but the codes require the breaker to be at least 120% of any single largest load, meaning everything has to be sized bigger and the next normal step up is 30A. If they wired/rated the compressor and the backup heater separately, say 8A and 10A, I think you’d be allowed to wire it on that 20A circuit.

Since most people are installing them on circuits that were formerly for electric water heaters (30A or bigger), it probably doesn’t matter that much…
 
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tomuo

Member
Mar 15, 2021
49
17
Los Angeles, CA
to whom ever asked about the 20A service. It’s a bit irritating really. I believe it’s rated to 18A (230VAC) but the codes require the breaker to be at least 120% of any single largest load, meaning everything has to be sized bigger and the next normal step up is 30A. If they wired/rated the compressor and the backup heater separately, say 8A and 10A, I think you’d be allowed to wire it on that 20A circuit.

Since most people are installing them on circuits that were formerly for electric water heaters (30A or bigger), it probably doesn’t matter that much…
Agreed. This would have to be a permitted electrical installation, so can't get away with 20Amp.
My garage has a new sub panel with a 70amp feed, the old wires are still there but they're aluminum and look to be 12 AWG not 10, so 20amp max.
 

Dave EV

Active Member
Jun 23, 2009
1,921
1,615
San Diego
I have the Rheem HPWH. I’m very happy with it. It’s been very reliable and the internet features mostly work (drops the connection periodically for unknown reasons).

I wanted to make two suggestions. 1). Increase the storage size from what you have (we went 50 —> 80) so it can stay in HP mode most of the time. They are well insulted so the stand by losses are small.
2) remember the “waste” is a flow of cold, dry air. If you would normally be air conditioning or dehumidying, run a duct and use the “waste” from the HPWH and eliminate another appliance. That makes it very economical…. I use mine to cool a wine cellar 😎.
Good suggestions - personally, I have not had any issues with the WiFi connectivity of mine in the 1.5 years I've had it. The only weirdness has been around scheduling where the settings I thought I was making didn't always reflect what the heater was doing, but I haven't had that issue recently, either.

Upsizing from 50 to a larger tank is a good idea if you have the room - though around here the 80 gal versions are quite a bit more expensive than the 50 gal versions. I personally not not seen a drastic difference in heat-pump only mode vs "energy saving" mode where resistance does occasionally get triggered, but your mileage will vary depending on water usage, inlet water temps and ambient temps. Our HPWH definitely uses more energy in the winter than summer, for example.

An alternative (or in addition) to upsizing the tank is to install a thermostatic mixing valve set to 120F. This will let you safely increase the temperature and use the tank store more hot water, and/or you can also then time-shift your energy usage more effectively if you have TOU electricity rates. Raising the tank temperature will reduce the efficiency of the heat pump, though. It would be interesting to know by how much.

There has been talk about Rheem working to increase the maximum temperature of the HPWH from 140-150F or something (don't recall exact thresholds) to provide for the ability to store additional hot water for load shifting purposes.
 
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David.85D

Active Member
Oct 29, 2016
1,513
1,281
USA
Good suggestions - personally, I have not had any issues with the WiFi connectivity of mine in the 1.5 years I've had it. The only weirdness has been around scheduling where the settings I thought I was making didn't always reflect what the heater was doing, but I haven't had that issue recently, either.

Upsizing from 50 to a larger tank is a good idea if you have the room - though around here the 80 gal versions are quite a bit more expensive than the 50 gal versions. I personally not not seen a drastic difference in heat-pump only mode vs "energy saving" mode where resistance does occasionally get triggered, but your mileage will vary depending on water usage, inlet water temps and ambient temps. Our HPWH definitely uses more energy in the winter than summer, for example.

An alternative (or in addition) to upsizing the tank is to install a thermostatic mixing valve set to 120F. This will let you safely increase the temperature and use the tank store more hot water, and/or you can also then time-shift your energy usage more effectively if you have TOU electricity rates. Raising the tank temperature will reduce the efficiency of the heat pump, though. It would be interesting to know by how much.

There has been talk about Rheem working to increase the maximum temperature of the HPWH from 140-150F or something (don't recall exact thresholds) to provide for the ability to store additional hot water for load shifting purposes.
Mine tops out at 140F. We set it to 130F. It’s our house, so no issues with renters, etc.

My wife likes to feel like the shower is a lobster pot….

the local utility offered a $500 rebate for HPWH, so I put the extra money into the bigger tank…
 
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darhall993

Member
Jan 24, 2019
161
148
Sandy Springs, GA
Good suggestions - personally, I have not had any issues with the WiFi connectivity of mine in the 1.5 years I've had it. The only weirdness has been around scheduling where the settings I thought I was making didn't always reflect what the heater was doing, but I haven't had that issue recently, either.

Upsizing from 50 to a larger tank is a good idea if you have the room - though around here the 80 gal versions are quite a bit more expensive than the 50 gal versions. I personally not not seen a drastic difference in heat-pump only mode vs "energy saving" mode where resistance does occasionally get triggered, but your mileage will vary depending on water usage, inlet water temps and ambient temps. Our HPWH definitely uses more energy in the winter than summer, for example.

An alternative (or in addition) to upsizing the tank is to install a thermostatic mixing valve set to 120F. This will let you safely increase the temperature and use the tank store more hot water, and/or you can also then time-shift your energy usage more effectively if you have TOU electricity rates. Raising the tank temperature will reduce the efficiency of the heat pump, though. It would be interesting to know by how much.

There has been talk about Rheem working to increase the maximum temperature of the HPWH from 140-150F or something (don't recall exact thresholds) to provide for the ability to store additional hot water for load shifting purposes.
Dave EV makes a great suggestion with the mixing valve. We did that exact thing in a weekend home where space was very tight, a 50 gallon set to 140 with the mixing valve does the trick nicely, of course you can always flip to high demand mode if you have a full house!
 
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Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
6,110
11,698
Springfield, VA
I wonder what the efficiency drop is running at 140° compared to 125°. That’s a pretty big increase in head and differential pressures, so I’d imagine it isn’t insignificant. Over the life of the unit it’s probably cheaper to spec a larger unit than set the temp that high, if space isn’t a concern.
 
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tomuo

Member
Mar 15, 2021
49
17
Los Angeles, CA
I wonder what the efficiency drop is running at 140° compared to 125°. That’s a pretty big increase in head and differential pressures, so I’d imagine it isn’t insignificant. Over the life of the unit it’s probably cheaper to spec a larger unit than set the temp that high, if space isn’t a concern.

I think the common reason given for using the higher temperature is to kill the Legionella bacteria, so the actual temperature probably matters. It would definitely be interesting to see if there is a performance delta for raising that last 10 degrees.

On casual googling I only found anecdotal info about temp, until this:

• Water at 110 F is in the ideal breeding temperature for Legionella bacteria growth.

It also recommended that hot water generators be 135 F to 140 F. (The new ASHRAE Standard 188 and ASHRAE Guideline 12-2000 recommend storage temperatures in this range and a minimum distribution temperature of 124 F because Legionella bacteria can grow in temperatures up to 122 F. It survives between 122 F to 131 F but does not multiply.
So that would indicate setting the water heater as hot as it goes, and using thermostatic valves at point of use.
I'm actually working on that, I got these
which are easy to install under the sink.

A couple of months back I had the gas company come out to fix a small leak in their meter (the seal on the pressure reducer was bad), when the worker gave the (current, gas) water heater a visual check he had to turn the temperature down to the minimum, apparently their safety guidelines against scalding require them not to leave a system that way. I guess that would change if the mixing thermostat is visibly attached to the water heater, but not if the mixers are at point of use.
 

iPlug

Member
Sep 14, 2019
626
908
Rocklin, CA
To complicate matters, those who set their HPWHs to shut off during peak time-of-use hours would likely need to set the temp higher during off-peak running to compensate for fewer daily hours of available run time.

What is most cost effective, efficient, and maximal to renewable energy use don't overlap cleanly. YMMV.
 

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