Hot water Heat pump, anyone running them in their house?

[drps10]

Tried searching in here for a bit.

Time to replace 40 gal 4.2kw hot water tank. Been researching Heat Pump hot water tanks. I want people with real world number, not manufacture produced numbers. I think I’m going to go to a 80 gal (if I have the room). I know the recovery time is not as high with heat pump as normal electric tank, but having extra water will allow to have enough hot water for everyone without running out or the struggle to recover and still need the demand.
We are a family of 6 and rare we run out if all 4 kids need to shower, but I make sure I go first if needed .

Anyone have power draw for heat pump only or hybrid mode? How well does it actually recover hot water? What is your incoming water temperature when you are recovering? Where are you located? Where is the tank located in the house? Is it in a conditioned space, semi conditioned ( mechanical room with no direct heat but surround room is heated)? How large is the room? Notice a big temp drop in the room when pump is running? Average temp of the room that heat pump pulls air from? What about the floor above the hot water tank, is it ice cold from the exchange of air?

Just trying to think of questions that you normally don’t have to think about when buying a normal electric hot water tank. We use about 425kw for hotwater last month. That is the highest we have used since I’ve been monitoring it. We have cheap rate, so after taxes and all $45
Thanks

 

[DIYrich]

I just installed a HWHP. For 6 people, you will need a large unit.
Heat to 145 degrees, and Thermostatic Mixing Vavle to blend down to 120 degrees.

Thermostatic mixing valve - Wikipedia

en.wikipedia.org

I would start running in HP mode only, not hybrid. Then you will know if you need the resistance heating to boost daily usage.

My HWHP is located next to the furnace, so that helps in winter (waste heat from furnace is used constructively). About 200 sq ft unfinished area of the basement. In the summer, it is a nice way to get free cooling and dehumidification. When the HWHP first turned on, it really chilled the room (cold in winter). Once the tank was heated, I don't notice it, but it is just the two of us. You will probably notice it with 6 poeple.

Note: I'm not sure how beneficial HWHP is in the winter. The cool air has to be heated by the furnace. Energy comes from the Furnace, goes to the Room, then goes to the Water. You can't change the physics.

I have a boiler for backup hot water. I'll probably run it in the winter time, and run the HWHP in the spring/summer/fall.

I'm guessing it can recover about 15 gallons of water per hour. Don't know the incoming water temp. It uses about 500 watts per hour. you can assume a 3.2x factor to calculate the BTU's for your situation.

If your room gets chilled, then it will chill the floor above. If that is an issue, then consider insulating the ceiling.

80 gallon tank is about 95 gallons first hour delivery rate. If you heat to 145, and blend with 55 degree water to 120 degrees, then that is about 130 gallons the first hour.

 

[drps10]

Thanks for all the great info!

 

[Partimewages]

HPWH is 3-400% efficient compared to straight electric elements.
If you're coming from an electric WH you will save money.

 

[OffGridInTheCity]

I've been running a Rheemes 50gal in heat-pump only mode for several years. 2600sq foot house with ~300ft of hot water recirculation. Under the house with 55F low in winter and 75F hi in summer. Uses 150kwh/month summer and 190kwh/month in winter.

It runs at 400w max in heat pump mode but takes a couple of hours to heat up if you totally run out of hot water whereas the 4500w heating element is faster. I think it's ~27w idle. Not a problem for us.

*The only downside with Rheemes is that it insists on 'testing' the 4500w elements when 1st turned on - so you can't get away with a just a 400w inverter, you need an inverter that can handle a short duration at 4500w.

 

[drps10]

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[drps10]

I've been running a Rheemes 50gal in heat-pump only mode for several years. 2600sq foot house with ~300ft of hot water recirculation.

How many people in the house?

Great info! Didn’t know about the “test” of the elements.

 

[drps10]

HPWH is 3-400% efficient compared to straight electric elements.
If you're coming from an electric WH you will save money.

I do know I’ll save money, but at what “costs”? Does it take to long to recover? Does it make my non conditioned laundry room ice cold now? Does the tile floor above it now always ice cold too?

I like saving money and being more efficient, but sometimes I’m not willing to give up some creature comforts

 

[Partimewages]

I haven't read the specs sheet but there is likely a minimum Sq/ft requirement. All of them I have been involved in were in basements.

 

[Bob in Tucson]

Does it take to long to recover?

That will depend on the air temp and the amount of water it needs to heat. If everyone showers at the same time, it's likely going to work for at least a few hours in HP mode. If the showers are scattered, it'll likely keep up, unless the room it's in is quite cold.

I like saving money and being more efficient, but sometimes I’m not willing to give up some creature comforts

It's counterintuitive, but it uses slightly less energy in 'energy saving' mode, which allows it to use the heating elements, than in 'HP only mode.' I read it somewhere and didn't believe it, so I tried it. True for me too. So if you are in a jam and need it to operate like a 4500 w unit, it will, provided you give it that option.

 

[OffGridInTheCity]

How many people in the house?

2 of us. We 2000-2500gal/month of water.

 

[1201]

I've been running a Rheemes 50gal in heat-pump only mode for several years. 2600sq foot house with ~300ft of hot water recirculation. Under the house with 55F low in winter and 75F hi in summer. Uses 150kwh/month summer and 190kwh/month in winter.

It runs at 400w max in heat pump mode but takes a couple of hours to heat up if you totally run out of hot water whereas the 4500w heating element is faster. I think it's ~27w idle. Not a problem for us.

*The only downside with Rheemes is that it insists on 'testing' the 4500w elements when 1st turned on - so you can't get away with a just a 400w inverter, you need an inverter that can handle a short duration at 4500w.

What's the duration of this 4500w burst? Because 400w for two hours or 0.8kwh total to get 50 gallons from 75f to 120f is a pretty high cop.

 

[OffGridInTheCity]

What's the duration of this 4500w burst? Because 400w for two hours or 0.8kwh total to get 50 gallons from 75f to 120f is a pretty high cop.

The 4500w spike I'm talking about is like it's testing things when it first turns on. I immediately cycled the options to heat-pump only mode and after that the traditional heating elements are ignored. It has several options from 100% heat-pump to 100% heating element and inbetween.

If you're asking how long it takes 100% heating element to heat water up - I don't know as I've always run in heat-pump only mode but I assume it's faster.

 

[1201]

The 4500w spike I'm talking about is like it's testing things when it first turns on. I immediately cycled the options to heat-pump only mode and after that the traditional heating elements are ignored. It has several options from 100% heat-pump to 100% heating element and inbetween.

If you're asking how long it takes 100% heating element to heat water up - I don't know as I've always run in heat-pump only mode but I assume it's faster.

I'm asking if you're saying that it only takes 0.8kwh to get 50 gallons from cold to hot

 

[OffGridInTheCity]

I'm asking if you're saying that it only takes 0.8kwh to get 50 gallons from cold to hot

Don't know. When I said 'a couple of hours' I mean that if the water runs cool after a few loads of laundry, it takes a couple (2-3) hours to get *hot* again. We set ours to 125F. I haven't done any testing other than at 11c/kwh (our grid at install year) it was cheaper than natural gas as in $16 - $22 / month vs ~$30/month.

Here's what I installed - https://www.rheem.com/heatpumpwaterheater/ - maybe you can find the specs you're after.

At the time (Nov 2021) it was only $300 with rebate from Home Depot. I think these days they're closer to $1800!

 

[kennyb]

Usage rheem 40gal hp. 2 adults, 1 toddler. Hp only mode.

 

[OffGridInTheCity]

Usage rheem 40gal hp. 2 adults, 1 toddler. Hp only mode.

I think the location / ambient temps make a difference, as well as amount of hot water - e.g. we do ~300ft of hot water recirculation for 'instant hot water' at the bathrooms at opposite ends of the house.

Here's my kwh/month the last 2 years with (I think) the major factor being ambient temp under the house of 55F winter and 75F summer. I presume that attic install with higher temps would make it significantly more efficient. On the other hand, I'm surprised it works as well as it does at 55F

 

[OffGridInTheCity]

I found this link to some specs but not sure of exact Rheems model - https://v3.myrheem.com/360/Rheem/WH/docs/hybrid-heat-pump-rheem-hybrid-heat-pump-spec-sheet.pdf

 

[kennyb]

I think the location / ambient temps make a difference, as well as amount of hot water - e.g. we do ~300ft of hot water recirculation for 'instant hot water' at the bathrooms at opposite ends of the house.

Here's my kwh/month the last 2 years with (I think) the major factor being ambient temp under the house of 55F winter and 75F summer. I presume that attic install with higher temps would make it significantly more efficient.
View attachment 197476

Ontario Canada, Lake Huron/Georgian Bay area. Inlet is ducted to the high point of the space (16ft). Outlet is ducted internally. Average indoor temps are between 18-22c usually . The space wood heated. Usually run the heater at 64c, but have it set to turn down overnight and then ramp up during daylight hours.

 

[OffGridInTheCity]

Ontario Canada, Lake Huron/Georgian Bay area. Inlet is ducted to the high point of the space (16ft). Outlet is ducted internally. Average indoor temps are between 18-22c usually. Wood heated.

Yes sir, I considered piping heated air (from the house) to the water heater as water heater has a round input hole that would make this reasonable easy to do but since it works OK, and we're in a mild climate zone where 55F low is the lowest it will ever get - I didn't make the effort