• Have you tried out dark mode?! Scroll to the bottom of any page to find a sun or moon icon to turn dark mode on or off!

diy solar

diy solar

Heat Pump water Heaters

You should only vent your WH outside if intake and exhaust are both connected to outside
I know we are talking Heat pump, but be careful how you word this!

I think the point you are making is, the supply and return airflow both need to go the same place.

This is correct.

If you have the supply venting cooled air into the living space, the living space needs to supply the return air, otherwise airflow issues could compromise the heatpump airflow.
 
I know we are talking Heat pump, but be careful how you word this!

I think the point you are making is, the supply and return airflow both need to go the same place.

This is correct.

If you have the supply venting cooled air into the living space, the living space needs to supply the return air, otherwise airflow issues could compromise the heatpump airflow.

Yes, that is what I meant. Because I get triggered when people exhaust HPWH to outside, with the intake coming from inside. There are many situations where that is bad in terms of energy efficiency, as well as uncontrolled infiltration of make-up air.

And there are other bad configurations too.
 
HP's are just a better use of power, especially in warm'ish climates where the HP is in the garage or out of the living space.

I see COP's well over 4 in the summer with mine.
Sure but you could also have gotten a 120V only one to achieve that goal. You did some extra work, it would be helpful for others to understand the logic.

I can imagine some advantages over hacking a 240V one, like better equipment availability, or preferring 240V for better inverter leg balance, lower resistive drop, or lower current/surge, or preferring the ability to reverse the decision to go HP only.
 
Having the heat pump water heater in series ahead of my propane water heater has worked out well this winter. If forecast is endless days of low PV yield or it might be cloudy for a few days and SOC is below 80%, I turn off the heat pump water heater via the app. We had to run 3 weeks in December solely off the propane water heater, we just had no excess PV available. I have it off again today, I turned it off yesterday noting forecast is light snow and knew it would be cloudy and SOC was under 80%. Propane is cheaper than buying electric off the grid, even with a heat pump water heater.

As the heat pump water heater is in the uninsulated basement with a feezer, charge controllers, inverters and battery bank, there is some heat from those items. If it was -20°F, then I would run just off the propane simply due to not getting the basement too cold thus affecting heat pump efficiency. With the heat pump water heater running, in the morning I have seen a low of 11°C for battery temp which is around 51°F. I think the potatoes and onions from the garden like it.
 
The only time that the Rheem will kick on the elements is when it is too cold to run the compressor, and that is somewhere under 25f. I've had the 'normal' 240v unit for 3 years now and only two days has it ever run the elements locked into HP mode.
Mine is just over 2 years old now. I run off a split phase inverter with a dedicated WiFi power meter on the Rheem. In both eco and HP modes the elements kicked on from initial cold start, and a while later when I ran radiant floor heat and ran the tank down to 80 degrees.
I can only surmise that there may have been complaints about heater performance in HP only situations and they changed the algorithm in the later model to turn on the elements under unusual operating conditions. Understandable if that’s what they did.
 
The only time that the Rheem will kick on the elements is when it is too cold to run the compressor, and that is somewhere under 25f. I've had the 'normal' 240v unit for 3 years now and only two days has it ever run the elements locked into HP mode.
My new 65 gallon Rheem Proterra kicked on both the elements and the heat pump when I first filled it with cold water, even though it was set on heat pump only mode. Apparently it sensed that the water in the tank was too cold for the heat pump alone. I thought it was defective but it has been working perfectly in heat pump only mode ever since.
 
If run in heat pump mode only, my Richmond might kick on the element on a cold start. Switching to Energy Saver mode, I haven't seen the element kick on with a cold start.
 
Sure but you could also have gotten a 120V only one to achieve that goal. You did some extra work, it would be helpful for others to understand the logic.

I can imagine some advantages over hacking a 240V one, like better equipment availability, or preferring 240V for better inverter leg balance, lower resistive drop, or lower current/surge, or preferring the ability to reverse the decision to go HP only.
There weren't many(any) 120v only models commonly available 3 years ago.

Plus, they didn't qualify for the $500 rebate my EMC was giving at the time for whatever reason.
 
The only time that the Rheem will kick on the elements is when it is too cold to run the compressor, and that is somewhere under 25f. I've had the 'normal' 240v unit for 3 years now and only two days has it ever run the elements locked into HP mode.
I have the elements kick on any time I start the system from empty. They run with the compressor until the water is at 40c and the shutoff. My tank is an older 2019 model, so the gen 4(I think) may be different.

Nvm....I see you address that later in the thread. Whoops
 
What are your personal reasons to HP only via buying and modding a 240V?

Did you also consider switching to lower wattage elements?
This may not have been intended for me, but here goes anyway.
My current inverter tops out at 8kVA. If elements turn on when I’m using other heavy loads, there’s not enough power.

Like most people reading the manual, the term “ HP only” is presumably just that. Unfortunately with my model it’s more like “Mostly HP”.

Again for my application, forcing HP only by disconnecting the elements works to my satisfaction, and this way I know for sure I won’t get the extra 4.5kVA demand from the elements, regardless of situation or potential FW updates.
 
This may not have been intended for me, but here goes anyway.
My current inverter tops out at 8kVA. If elements turn on when I’m using other heavy loads, there’s not enough power.

Like most people reading the manual, the term “ HP only” is presumably just that. Unfortunately with my model it’s more like “Mostly HP”.

Again for my application, forcing HP only by disconnecting the elements works to my satisfaction, and this way I know for sure I won’t get the extra 4.5kVA demand from the elements, regardless of situation or potential FW updates.
Thanks. This is super helpful.

How did you disconnect the elements? Is it possible to do it with a relay?
 
My new 65 gallon Rheem Proterra kicked on both the elements and the heat pump when I first filled it with cold water
I think this is a "check the tank has water in it" test. It also makes sure the elements are not open circuit.
Both hit the elements for a few seconds.
 
Thanks. This is super helpful.

How did you disconnect the elements? Is it possible to do it with a relay?
Literally I removed the cover plate, and unscrewed the wires from the elements.
Service power disconnected of course.

Incorporating a relay would be nontrivial.
 
Can you put one of these units in a very small detached "closet" if the venting is too the outdoors?
Can be vented to the inside or outside. There are no combustion gasses.
I would like to see a kit to vent indoors in the summer and outdoor in the winter if conditions are right.
 
Can be vented to the inside or outside. There are no combustion gasses.
I would like to see a kit to vent indoors in the summer and outdoor in the winter if conditions are right.
If I get around to it this year I'm going to move my intake to the attic just above the unit. It is always going to be warmer up there than it is in the garage, no matter if winter or summer.

Just need to find the time.
 
I looked into hp water heaters when I thought our on demand hopped the twig, but it's OK now after a lucky fix. Our place is too small for anything inside. I'd thought of putting it just a foot or two away from the house, or even in a sort of attached closet, but wasn't sure if this was what the venting was designed for. Dumping either hot or cold air would be nice depending on the season, but we have basically a drafty toung and groove structure, with no insulation. Wood stove in winter, and the 12k minisplit only takes the edge off till 1pm on hot days. I can't imagine these hpwhs move much heat to maintain temp, and heating up replenishment water might not happen when a boost to the house is needed. Summertime is generally fans and everything open. Heating water is generally where all our propane goes. We seem to use a 500gal tank (half really - 80-30%) in a bit more than two years. Maybe that will change when the girls are teens. The on demand Rheem is rated for three teenage girls, and I'll have two, so should be covered.
 
I use HP only during summer months works great with the hot garage here in Phoenix. Tired it in the winter just takes too long to heat the water now that we are going from low 30s to high 50's. It was running for 3-4 hours trying to heat I set it back to energy save mode. This morning after my morning shower took about 3.6KWH to heat back up.

It also has a 120F degree mixing valve that mixes cold water with hot recirculates hot back into the heater they set the water heater to 140F. I was part of a pilot program my utility offered in return they installed a free heat pump water heater. They wanted to turn off the water heater during high peak demand rely on hot water and the mixing valve to sustain it through the 4 hours when the heater was shut off. Didn't work too well always seem to shut it off after someone showered wasn't much hot water left until they turned it back on. I set the heater back to 120F now that the pilot program is over. Overall probably save little not heating it to max heat of 140F.
 
We seem to use a 500gal tank (half really - 80-30%) in a bit more than two years. Maybe that will change when the girls are teens. The on demand Rheem is rated for three teenage girls, and I'll have two, so should be covered.
Sounds about right for propane usage, tank type will take slightly more. 200 to 300 gallons of propane per year depending on household size. I know between installing a heat pump water and using heat pumps for heating the house when we can has cut propane usage from about 600 to 700 gallons per year down to under 400 plus we can zone high usage rooms at a higher temp.

Yes, you can install in a closet and use a venting kit. However, when the compressor is running it will not be quiet. This is important. Mine is in the basement and I can hear when it is running. Just a slight droning sound upstairs. In a closet upstairs would not be pleasant.
 
I've really been trying to figure out how to go to a straight demand HWH. I will probably need the 3rd inverter to do it, I think I could get by with around a 12-15 KW unit, but The HVAC on top of that puts me really close to 24KW.
 

diy solar

diy solar
Back
Top