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Heat-Pump Water Heaters

Posted on Oct 13 2009 by Alex Wilson

There’s a revolution underway with electric water heating. It could be just as significant as the shift from top-loaders to horizontal-axis front-loaders that we’ve seen in the laundry appliance industry.

For years, electric water heaters were simply insulated tanks with a couple of electric-resistance elements that heated the water. These have worked pretty well, and with the highest-insulation products, the “Energy Factor” (a standardized measure of efficiency that factors in losses through the insulated tank) of the best products get pretty close to 1.0 (100% efficient).

Within the past few months, at least three electric water heaters have been introduced that double this efficiency. These are heat-pump water heaters. Rheem offers the 50-gallon HP-50; the German company Stiebel Eltron introduced in the U.S. the 80-gallon Accelera 300; and North Road Technologies offers the “retrofit” Geyser product that connects to a conventional electric or gas water heater.

These new products join a couple of retrofit heat-pump water heaters already on the market (the E-Tech line, now made by A.O. Smith, and the AirTap made by AirGenerate). And next month, GE is set to introduce its own heat-pump water heater, which the company calls a “Hybrid” water heater.

How does a heat-pump water heater work?
Instead of using electricity directly to heat water, a heat-pump water heater uses electricity to move heat from one place to another--in this case, from the surrounding air where the unit is located into the water. This is done by circulating a special “refrigerant” fluid that can be alternately evaporated into a gas and condensed into a liquid by changing its pressure.

Surrounding air is drawn into the heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. where the heat in that air vaporizes refrigerant in the “evaporator,” releasing cooler air into the room. The refrigerant vapor is then pumped through a “compressor” where it condenses back into liquid form and releases its stored heat into the water.

All this sounds pretty complicated (and, well, it is), but this “refrigerant cycle” is well understood and widely used in both refrigerators and air conditioners.

More about heat-pump water heaters
The benefit of a heat-pump water heater is that you get at least twice as much hot water from each kilowatt-hour of electricity consumed as you get from a standard electric water heater. The Energy Factors of these units range from 2.0 to 2.5--meaning that they are, effectively, 200% to 250% efficient at converting electricity into heat. With new Energy Star standards for water heaters now in effect, among electric water heaters only heat-pump models make the grade. This will significantly spur interest in the technology.

A disadvantage of heat-pump water heaters is that they rob heat from the room where they are located. In the winter, this means that they can increase heating costs. If you heat with electricity, this eliminates much of the benefit of the heat-pump water heater during the winter months, but if you heat with less expensive gas, oil, or wood, you should still realize significant savings. The units are often installed in “semi-conditioned” space, such as a basement or garage, but they should not be put in a space that can drop below about 40 degrees.

While extracting heat from the room is a drawback in winter, it’s an advantage in the summer. During warm months, heat-pump water heaters provide free air conditioning and dehumidification--because they cool air as it is circulated through the heat pump. For this reason, heat-pump water heaters are likely to find the most receptive buyers in warmer climates.

A condensate drain line has to be installed to remove water that condenses out of the air as heat is extracted and the air is cooled. This can complicate installations, especially in basements of existing houses.

Be aware that the fan in a heat-pump water heater (which draws air through the unit) makes some noise. The sound levels of the products on the market range from 49 to 64 decibels (dB), which is on the same order of magnitude as a refrigerator.

Finally, heat-pump water heaters are expensive. Suggested retail prices range from $700 for the retrofit AirTap model (which still requires a storage water heater) to $3,500 for the largest, integral-storage Stiebel Eltron (which offers the highest efficiency of any of the products). The Rheem HP-50 has a typical contractor price of $1,300 to $1,500, and the Stiebel Eltron $2,500. The need for installing a condensate line will further increase the installation cost. More on heat-pump water heaters can be found in the October 2009 issue of Environmental Building News (log-in required).

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Image Credits:

  1. North Road Technologies Geyser
  2. Rheem

Oct 16, 2009 6:43 AM ET

Heat Pump DHW & Solar THermal
by R Porter

I have seen the promises; and we have seen some local production builders adopt heat pump DHW as a standard item in their product. We have also seen the introduction of heat pump technology that "borrows" from the existing HVAC units to augment DHW energy consumption. What I would like to see (and may experiment to find out) is the effectiveness of combining the solar thermal technology with a small scale heat pump used to augment heating during extended cloudy periods, or as a trade-off for volume (80 gal vs 160 gal tank/arrays). Any thoughts? Heat transfer technology has come a long way, and I believe we are on the verge of practically eliminating the "cost" of energizing our DHW needs in residential construction (a significant source of aggregate energy consumption in every climate zone and season).

Richard Porter
Bungalow Building Services
Bradenton, FL

Oct 16, 2009 10:58 AM ET

Heat pumps and solar
by Alex Wilson

I too have been wondering about this. At the commercial scale, it is not uncommon to extract usable heat from various waste flows and boost the temperature of that waste heat using water-source heat pump technology. I believe that solar could be used as a similar heat source, and I'm sure it's been tried--but I don't know where. If you try it out, keep me posted:

Oct 18, 2009 2:29 PM ET

commercial use?
by Brent Eubanks

Are any of these suitable for (at least) light commercial applications?

Nov 12, 2009 12:00 AM ET

Commercial Hot water with 5 tons A/C as bi-product
by Heidi Veres

We manufacture a product that uses indoor heat and humidity to heat large quaninties of water with R410-A and a cupronickel heat exchanger, that also cools air 15 degrees, that is re-circulated in the A/C ductwork. These are a perfect for retrofit or design build. Unit can be installed up to 150 feet away from water tank and is a great solution in high heat areas in buildings such as kitchens, sanitation and laundry. ROI is around a year. This product can save a restaurant around $700.00 a month in electricity.

Jan 4, 2010 4:07 AM ET

Heat Pump DHW, Solar Thermal, and Hydronic Radiant?
by Michael Schonlau

I'd like to take R Porter's comments above a step further - how about combining solar thermal with a DHW heat pump to also provide hydronic radiant floor hot water needs? Is it feasible?

Jan 15, 2010 2:30 PM ET

Rheem HP-50
by Rick

OK now where do I buy one of these heaters.

Jan 15, 2010 2:58 PM ET

Just do some Web surfing
by Martin Holladay

It's available online if you can't find it locally. Do you have $1,495 plus shipping and installation?

Feb 1, 2010 11:36 PM ET

Residential and Commercial Heat Pump Water Heaters
by Heat pumps rule

Replacing a fossil fuel or standard electric water heater with green heat pump technology makes a lot of sense. Upgrading a solar system back-up with a heat pump water heater is also smart. Some "worry" about using heat they already paid but are perfectly happy with an existing water heater meerly 80 to 95% efficient. Does not make much sense. In a perfect world, pipes, ducts, air handlers, furnaces, clothes washers and dryers and water heaters never have standby heat losses. In a real world, all this waste heat can be captured - recycled by a heat pump and concentrated in a water heater tank where it is needed. Some call it redistributed energy. Find more information on commercial & residential HPWH, performance data and myth debunking at

Feb 2, 2010 12:09 AM ET

Geyser more flexible than integrated heat pump water heaters
by John DaSylva

A modular heat pump water heater such as Geyser is a better alternative to integrated heat pumps. When the tank fails, just get a new tank. It converts any existing water heater tank to efficient heat pump technology in just 30 minutes. They can be ducted and be connected to an air exchanger via a thermostatic damper to extract heat before stail air is exhausted. They have a built-in circulation pump so they are really easily to convert as a true whole house instant hot water system. Just can't do that with an integrated tank. Installation video at:

Feb 2, 2010 12:17 AM ET

Rheem Recall
by Paul Lantana

Do not know if this is true but rumour has it that Rheem heat pump water heaters have been recalled because they tested 1.6 EF and do not meet the minimum 2.0 to qualify for Energy Star. The General Electric looks smarter and is likely a better buy, but it is huge.

Feb 28, 2010 9:14 PM ET

One should consider the
by Zee

One should consider the following parameters when selecting electric heat pump water heater:

* The heating coefficient of performance, COP, is used for the performance, and it defines the ratio of heat energy of heat pump to the electrical energy unit.

* Energy Factor or EF is the ratio of heat output to energy input. An average value for heat pumps is between 2 and 2.5 (for reference; maximum EF for electric water heater is close to 1).

* The first hour rating.

Mar 14, 2010 11:52 PM ET

Heat pump water heaters?
by Ronald Sauve

Maybe I'm too dense to figure this out, but isn't heating water with one of these units like trying to cool your home by leaving a refrigerator door open? It would seem to me that you have a situation with a bit of a conflict of interest, so to speak. Yes, you're heating water with heat from the house, so it's not directly fighting, but although you have a more efficient water heater, you're paying for it, at least in part, with the money you've already paid to heat your house. I suppose arguments can be made that there might be some efficiency tradeoffs where you come out ahead in the end. And I could almost see using them in the south where there is no need for heat; at least they could then help out with the AC, and not be working against trying to heat the home. But, why not just let the heat and DHW each stand on their own merits?

Apr 6, 2010 1:59 PM ET


I 've had an Airtemp HWHP for 25 years. It's automatic controls are starting to die, so I turn it on and off manually. I'm looking for another one as no one can fix this one. I live in a Northern state and use it late April to the end of October. My electric bill drops $25.00 when I put it on. It totally airconditions my house in the summer. I have to decide what unit to get ,I want a add on unit like geyser.

Apr 7, 2010 8:50 PM ET

air generate
by Anonymous

check out there site. i am looking into something like this as well. still undecided.

May 3, 2010 10:29 PM ET

Heat Pumps
by Geothermal Heat Pump

Heat pumps are nowadays making so much pollution ! Use eco -friendly Geothermal Heat Pumps !

May 20, 2010 1:48 PM ET

New water heater using wind power
by Zman

I just read an article about water heaters on wind. Some students from the university started designing a water heater that is using wind power to run the water heater.

I would like to hear more about their progress but cannot find info. If anyone knows please let me know.

Jun 17, 2010 12:01 PM ET

Using the heat pump
by Zee

How much does the efficiency drops during the winter time when there is no much heat to extract from the air? When the air is colder more energy is needed to heat the water, right?

Jun 17, 2010 12:59 PM ET

H-P water heaters in winter
by Alex Wilson

This is correct. Performance drops in the winter, because the heat pump is extracting heat from air that's at a lower temperature. How much the efficiency drops will depend on the air temperature; you'd have to ask manufacturers for that data. In the summer, that drawback becomes an advantage, because the H-P will provide some free air conditioning. -Alex

Jun 18, 2010 7:22 AM ET

HP Water heater additional benefits
by Bill

I am seriously considering the RHeem HPWH as a replacement for my electric one. My current electric water heater is on the main floor of our home in the utility room, which you have to walk by coming in from the garage. I don't think I want the HPWH in there as the fan may be noisy. My plan is to relocate the water heater to the basement, which is not conditioned, where I also have a dehumidifier. I expect multiple gains based on the fact that the HPWH is more efficient and I can then possibly discontinue usage of the dehumidifier or at least the dehumidifier would have less work to do. Any comments about my thoughts? Thanks....

Sep 14, 2010 9:58 AM ET

electrical elements are the
by Fire Fly

electrical elements are the cheapest to install, however they are the most expensive to run. They use 1 kW of electricity to produce 1 kJ heating energy into the water. In an average South African home is normally a 200 L Geyser it utilises a 4 Kilowatt element to keep the water. Every time you switch on your taps at home cold water refills the water in your geyser and those 4 kW element switches on. Now with heat pumps all you are doing is disconnecting the antiquated technology and replacing it. Heat pumps will use 1 kW of electricity to produce 4 kilojoules of heating energy into the water this means it has a coefficient of four is to one.

Oct 19, 2010 12:30 PM ET

Geyser Heat pump
by jd

Just installed mine. Works great.

I heated 62 gallons of well water to 120 degrees F and used 3.7 Kw.
I should point out that I have a wood stove in my basement and the ambient temperature was probably in the high seventies the whole time,

Air cleaner, free distilled water, dehumidification, dirt cheap hot water!
I shut off my electric water heater and use the GEyser exclusively (familily of four)
all for a thousand bucks---attentitve tech help.
if my water heater springs a leak (or if I move) i can connect it to another water tank

Nov 30, 2010 4:12 AM ET

"Wave" domestic heat pump
by wavehp

"Wave" domestic heat pump water heaters can reach the COP of 4.0 in ambient temp 20C. This brand of heat pumps are refrigerant-free in tanks, meaing that all the heat exchanging is done in main units (outdoor units). Their website:

P.s. To Brent Eubanks: You should chose a commercial heat pump for commercial use. They are not same with domestic units.

Apr 24, 2011 6:30 PM ET

Hybrid Water heater condensation amounts
by Gregory Swett

Anyone have amount of condensate produced by Hybrid Water heaters? Have purchased a GE unit but having problems with the HOA. There is a currently installed overflow lines going to drywells which is the planned disposal route. GE says up to 24 gallons per day which they use to size a condensate pump. Ambient temperature is 75+ so heat pump mode will approach 100%. Occupants in the condo is two people. Currently about 200 kW is related to hot water heating. The unit is going into Hawaii where the kW cost is currently at $.40 and the humidity high. Any help or expereince would be appreciated.


Jun 23, 2011 12:48 AM ET

They Don't make Sense nor free heat
by Jim Olson

Just as the article says, they move heat. You don't gain anything unless you are getting the heat from a renewable source such as OUTSIDE air, ground, water, solar.... not the room air that you just paid to condition.

They don't make sense unless the heat pump is outside and then it will only work part of the year in most climates

Jun 23, 2011 11:40 PM ET

Be aware of lower rate of recovery of hot water for HPWH
by Ed Shank

Pay close attention to the published data for first hour rates of hot water recovery. Unlike gas water heaters that have a high rate of recovery, electric water heaters (both resistance type and heat pump type) have a lower rate of recovery. The hybrid heat pumps cannot keep up with high demands for hot water (like teenager's long showers or multiple uses of wot water appliances - dish washer and clothes washer running simultaneously). The heat pump side of a hybrid works fine at its published EF's when the high loads are gone but with high hot water loads the unit will soon be using its electric elements at an EF of just under 1 to try to keep up. There is no such thing as a free lunch and I find these hybrid units to be at best an expensive compromise.

I will wait until the Asian manufacturers begin importing their CO2 refrigerant based HPWH that can generate water hot enough to heat houses (like up to 160 to 170 F) as well as for domestic hot water. Google the words ECO CUTE CO2 HEAT PUMP and you will see they use outdoor units to generate the hot water, so there is no winter time penalty of robbing heat from the home, but also no free cooling in summer. They sell these in Japan by the hundreds of thousands. I find it curious they are not sold in North America.

Jun 24, 2011 4:21 AM ET

Response to Ed Shank
by Martin Holladay

When I reported on Japanese Eco Cute water heaters in the June 2007 issue of Energy Design Update, the average price of these water heaters in Japan was $5,800. I'm not sure if Americans are ready to pay that much for a water heater.

Jul 1, 2011 12:05 AM ET

ECODAN instead of ECOCUTE?
by Ed Shank

Thanks for the info Martin. At that price point, perhaps a better solution for the NA market would be something like the ECODAN sold in the UK that is an air source heat pump heating hot water for radiation in their buildings and also for their domestic hot water needs. One appliance can then supply all heating requirements. Have you explored these units installed costs? At their exceptionally high performance levels, I would suppose an argument can be made they would give a good ROI that would likely give geothermal systems a run for the money. (Assuming of course we could buy them in NA, of which I am only aware of the Daikin system available here)

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