Heat Pump Water Heaters

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

EbS-P

Minister of Fire
Jan 19, 2019
3,039
SE North Carolina
I'd like to put one in, but our pit basement has no drain. It makes me nervous to rely on a condensate pump down there, year after year.
We have an up flushing bathroom in the basement that the condensate is drained to . In 10 years we have only had the pump that was connected to the kitchen/washing machine fail due to a bad micro switch. Kitchen was removed and the other pump replaced (it was still working) it was 21 years old. I’ve gotten the 9v battery powered moister alarms all over the house since our previous water heater developed a slow leak. They are another failure point for sure. I’m considering a mini split for the basement and it will need a condensate pump. That’s not factoring into my decision to install or not. Evan
 

laynes69

Minister of Fire
Oct 2, 2006
2,671
Ashland OH
So question of the day? Currently I have our heater at 150. When it was 120 we would quickly run out while trying to fill the soaking tub. The hotter water allowed for more then tempered to a comfortable level. If the 80 gallon tank holds more water, could I keep it at let's say 120 and it would use less energy and keep up with the tub?
 

EbS-P

Minister of Fire
Jan 19, 2019
3,039
SE North Carolina
Our 80 gallon is set to 125. Only time we ran out was after the dishwasher ran, 1 soaker tub then 2 kids tubs. I’m not sure the soaker was super full might have been some sink dishes too. If you are you are worried about it you could use old 80 gallon as storage tank. But it would need electric and a second circuit. Probably overkill. Cant buy 80 gallon resistive WH now. You have 80% more capacity and really only running the tank temp (150) gives 30 degrees witch assuming 60 cold water is (to make math easy) only 50% higher so my fuzzy math says 80 is more than 50. Go for it
 

brenndatomu

Minister of Fire
Aug 21, 2013
7,328
NE Ohio
If you have the room, you could have the HPWH "preheat" the water going into your existing tank...then if the hot water in the HPWH is depleted, along with the 80 gall electric heater too, the electric heater would kick on as "backup"...that way the HPWH could be left on HP only for highest efficiency. As far as lowering the temperature...obviously you will have higher standby losses at 150* vs 120*...but I guess having 2 tanks would mean the same thing...unless you add aftermarket water heater blanket(s) on them maybe.
Or, you could leave the power off to your existing WH, then have it plumbed up so the water will thermosiphon between the HPWH and your existing one...HPWH heats it all, but you have 160 gallons hot and ready to go.
Oh, and you could maybe back off to the 50 gallon HPWH in this scenario too? I think they recover the same GPH...at least in HP only mode, if not in all modes.
 
Last edited:
  • Like
Reactions: sloeffle

laynes69

Minister of Fire
Oct 2, 2006
2,671
Ashland OH
I haven't thought of two heaters, but we try to spread out the usage if possible. I guess I try a larger unit and see where it goes. I ordered a clamp on ammeter that will be here tomorrow, so I will be doing some investigating.
 

Solarguy3500

Feeling the Heat
Dec 3, 2020
250
Western MA
Sounds like no matter which way you go, you could benefit from solar PV. Might be worth talking to a reputable installer in your area.
 

CaptSpiff

Minister of Fire
Jan 13, 2014
551
Long Island, NY
If you have the room, you could have the HPWH "preheat" the water going into your existing tank..
I did that for a friend. It's working great.
She had a failed 80 gallon electric replaced with a 50 a few years back. I had bumped up the temp setting twice because she was running out of hot water, but I didn't like the fact that the water was scalding my hands. She didn't mind.
Then she came across a HPWH rebate offer that made it almost free. I installed it in series, as a pre-heater to the perfectly good 50. Then I lowered the setting on the 50 to normal and wrapped an insulation blanket around it.
The HPWH does the heavy work in HP only, and delivers hot water to the 50, which hardly comes on at all.
Now I don't burn my hands and the dishwasher still does a great job despite the water temp being 15 degrees less.
 

laynes69

Minister of Fire
Oct 2, 2006
2,671
Ashland OH
I did that for a friend. It's working great.
She had a failed 80 gallon electric replaced with a 50 a few years back. I had bumped up the temp setting twice because she was running out of hot water, but I didn't like the fact that the water was scalding my hands. She didn't mind.
Then she came across a HPWH rebate offer that made it almost free. I installed it in series, as a pre-heater to the perfectly good 50. Then I lowered the setting on the 50 to normal and wrapped an insulation blanket around it.
The HPWH does the heavy work in HP only, and delivers hot water to the 50, which hardly comes on at all.
Now I don't burn my hands and the dishwasher still does a great job despite the water temp being 15 degrees less.
Hmmmm......How would that work usage wise? I take that the preheating would allow for the 50 gallon to not come on often, but to allow a much higher hot water capacity.
 

brenndatomu

Minister of Fire
Aug 21, 2013
7,328
NE Ohio
Hmmmm......How would that work usage wise? I take that the preheating would allow for the 50 gallon to not come on often, but to allow a much higher hot water capacity.
Correct...basically, you are building a 130 gallon HPWH...the electric could be left on to the existing heater, or turned completely off if you find it's never needs to kick on.
 

jetsam

Minister of Fire
Dec 12, 2015
5,337
Long Island, NY
youtu.be
Correct...basically, you are building a 130 gallon HPWH...the electric could be left on to the existing heater, or turned completely off if you find it's never needs to kick on.

It will still need to heat when nobody is using hot water, or else nothing is maintaining the setpoint against heat losses in the second tank. The second tank wouldn't need to heat much if the first tank was set to a higher setpoint and somebody used hot water every so often. (Super Store style dhw storage units deal with this via circulator pump.) And you are doubling the tank heat losses by having two tanks, but if the second tank is well insulated, that shouldn't be a massive hit. In terms of the electric bill I think you'd be money ahead to turn off the resistive unit and have a circulator pump run water back to the heat pump unit, but you are adding a lot of plumbing and a pump to your system (and probably incurring significant line losses too).

Unrelated, I ran a 50 gallon Rheem heat pump water heater in "HEAT PUMP ONLY" mode for a few months last year, and it does take a long time time get back up to temp when it's not allowed to use its resistive coils. We were running out of hot water once in a while with just 2 people. No issues since I changed it to go to eco mode ahead of our showers (but it uses a LOT more power now).
 
Last edited:

brenndatomu

Minister of Fire
Aug 21, 2013
7,328
NE Ohio
If it's set up right, the HPWH should heat the second tank via thermosiphoning, even during no usage times...I'd think most of the extra heat loss from having two tanks could be stopped by super insulating the tanks, especially the second tank.
 
  • Like
Reactions: jetsam

sloeffle

Minister of Fire
Mar 1, 2012
1,020
Central Ohio
Sounds like no matter which way you go, you could benefit from solar PV. Might be worth talking to a reputable installer in your area.
Not to go too far off topic.

I think we all can agree that we should get more our electricity from renewables. From the OP's perspective wouldn't it make more financial sense to conserve electric ( HPHW, turn computers off, etc ) vs spending an exorbitant amount of money on a solar system ?

Ohio has some of the worst incentives in the nation when it comes to installing solar. I priced out a solar system a number of years ago and the pay back was about 20 years. I chose to lease some solar panels at a fixed kWh hour rate for the next 15 years from my electric co-op vs buying.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,618
Grande Prairie, Alberta, Canada
Not to go too far off topic.

I think we all can agree that we should get more our electricity from renewables. From the OP's perspective wouldn't it make more financial sense to conserve electric ( HPHW, turn computers off, etc ) vs spending an exorbitant amount of money on a solar system ?

Ohio has some of the worst incentives in the nation when it comes to installing solar. I priced out a solar system a number of years ago and the pay back was about 20 years. I chose to lease some solar panels at a fixed kWh hour rate for the next 15 years from my electric co-op vs buying.

Exactly this. The general rule I keep hearing is 5:1. For every dollar invested in reducing electricity consumption, you save $5 on the capital cost of a solar PV system.
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,217
Eastern Central PA
I did that for a friend. It's working great.
She had a failed 80 gallon electric replaced with a 50 a few years back. I had bumped up the temp setting twice because she was running out of hot water, but I didn't like the fact that the water was scalding my hands. She didn't mind.
Then she came across a HPWH rebate offer that made it almost free. I installed it in series, as a pre-heater to the perfectly good 50. Then I lowered the setting on the 50 to normal and wrapped an insulation blanket around it.
The HPWH does the heavy work in HP only, and delivers hot water to the 50, which hardly comes on at all.
Now I don't burn my hands and the dishwasher still does a great job despite the water temp being 15 degrees less.
Why didnt you just turn up the water heater and install a mixing valve? Lots of standby by heat loss with 2 WH.
 
Last edited:
  • Like
Reactions: velvetfoot

velvetfoot

Minister of Fire
Dec 5, 2005
10,176
Sand Lake, NY
What's the current cost situation on propane vs. electric? Nobody's mentioned that, and you have a propane tank.
Are those new-fangled instant on gas water heaters any good? I would think tub-filling would be a good application for it.

Nobody's mentioned the noise of the hp water heaters-they can run for a long time.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,618
Grande Prairie, Alberta, Canada
What's the current cost situation on propane vs. electric? Nobody's mentioned that, and you have a propane tank.
Are those new-fangled instant on gas water heaters any good? I would think tub-filling would be a good application for it.

Nobody's mentioned the noise of the hp water heaters-they can run for a long time.

I've got an on-demand hot water heater, fueled by natural gas though. Mine is a Navien NPE-240A, 200,000BTU model, with built in recirculator.

Pro's:

Efficient
Small footprint
Never run out of hot water
Smart controller that ensures the lines are full of hot water at common use times, ie morning showers.
No steel tank to rust out.

Con's:

With an input temp just above freezing, and an output of 125F 4gal/min is all it puts out. Which I've found to be slow compared to tank style water heaters I've used for uses like, filling washing machine and bathtubs.
They need both gas and electric to function. Where with a tank style you still have hot water is left in the tank in the event of an outage.
Cost, mine was just over $4k, 3 times that of a traditional tank water heater.
Maintenance, the heat exchanger does need to be flushed with acid periodically to remove scale, this interval varies greatly with water quality.
Noise. The blower for the burner on mine does make some noise, especially if mounted to a wall and transmitted through the house, not a lot and this can be minimized with rubber isolators.
 
  • Like
Reactions: velvetfoot

begreen

Mooderator
Staff member
Nov 18, 2005
94,660
South Puget Sound, WA
Nobody's mentioned the noise of the hp water heaters-they can run for a long time.
The sound is reported to be about 45db, so fairly quiet and about the level of some wood stove fans.
 

brenndatomu

Minister of Fire
Aug 21, 2013
7,328
NE Ohio
Nobody's mentioned the noise of the hp water heaters
The Richmond HPWH is very quiet...only 49 dBA...really a non issue unless you are trying to watch TV right beside it...
 

Solarguy3500

Feeling the Heat
Dec 3, 2020
250
Western MA
Exactly this. The general rule I keep hearing is 5:1. For every dollar invested in reducing electricity consumption, you save $5 on the capital cost of a solar PV system.

That's a good point. I was making the assumption that the OP would exhaust all efficiency measures first, and then if the load is still high, it might be worth looking into solar. I should have qualified that in my post, and not made the assumption. I can't figure out how to edit my post now, or I would add something to that effect.

It is absolutely true that the cheapest energy is the energy you don't use, and one should always do efficiency measures before solar.
 
  • Like
Reactions: sloeffle

andym

Feeling the Heat
Feb 6, 2020
440
Hicksville, Ohio
I was just reading the technical data sheet on the Richmond HPWH from Menards. What are your thoughts on the ducted options? Is there ever a time you would want to intake or exhaust air from/to the attic? How about connecting the intake to a wood furnace? Just rambling here....
 

maple1

Minister of Fire
Sep 15, 2011
10,941
Nova Scotia
I was just reading the technical data sheet on the Richmond HPWH from Menards. What are your thoughts on the ducted options? Is there ever a time you would want to intake or exhaust air from/to the attic? How about connecting the intake to a wood furnace? Just rambling here....

I have thought that it might be beneficial to intake air from behind/under the fridge area. Ours always seems to be pretty warm back there. That's assuming water heater would be a level below the fridge and not far removed from it. Pretty sure I wouldn't hook it to a heat source, but you could maybe draw from the general area. And maybe pipe the exhaust to a spot you might want some slight chilling in the summer.
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,217
Eastern Central PA
I have thought that it might be beneficial to intake air from behind/under the fridge area. Ours always seems to be pretty warm back there. That's assuming water heater would be a level below the fridge and not far removed from it.
Dont bother, the HPWH can work down into the 40s efficiently. I have mine 3 ft from my furnace boiler so its usually high 70s there. The heat coming off your fridge is minimal.
 

brenndatomu

Minister of Fire
Aug 21, 2013
7,328
NE Ohio
I have thought that it might be beneficial to intake air from behind/under the fridge area. Ours always seems to be pretty warm back there. That's assuming water heater would be a level below the fridge and not far removed from it. Pretty sure I wouldn't hook it to a heat source, but you could maybe draw from the general area. And maybe pipe the exhaust to a spot you might want some slight chilling in the summer.
I wondered before if anybody offers a fridge/water heater combo...heat from the fridge goes into the water, cool from the water goes into the fridge...I'd think it could be done with 1 compressor unit too...would just need a line set between the 2 units...
 

laynes69

Minister of Fire
Oct 2, 2006
2,671
Ashland OH
It just so happens that our water heater is directly below our refrigerator, that doesn't seem like a bad idea. My oldest son brought home kill-o-watt meter and at a maximum output on his PC, it drew 365 watts. When he put it in sleep mode, it was 3 watts....so that's not too bad. I have a clamp ammeter and I'm currently investigating some of the usage, however I still suspect the water heater. I have to find the tape measure to see if I can house the 80 gallon hpwh, but I think I'll just have the room. It's talking the wife into spending the money, however I'm going to keep my eye out on a sale or just bite. Either way I'll save a significant amount on the electric bill.
 
  • Like
Reactions: sloeffle

Rob711

Feeling the Heat
Oct 19, 2017
443
Long Island, ny
How would you set up two heaters so that one would heat the other via thermosiphon. One of my “yeah I should do that” ideas is getting a 80 gallon HPWH. This is the first full year with solar and it looks like I produce almost double what we use, my issue, one of many, i proactively replaced the 18 yr 50 gallon old natural gas unit about a month before we decided to get solar.
I’ve talked about this here before and I felt the consensus was to ditch the gas one all together and just use a 80 gallon HPWH. My thoughts were to plumb gas heater first, turned off, feeding into the HPWH. It would make my mechanical room in the yet to be finished basement look odd. Against the wall in corner gas heater, then gas boiler for heat, then HPWH. I suspect my need for hot water will rise, 3 Girls from age 7-11 and wife.
Also thought in power outage I could still run house off my little 2200 Honda generator and still have hot water. I’m now realizing you’d have to blow through 80gallons before you got hot water if the power was out. Unless....I add a bunch of valves so I can bypass each. Idk.