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Demystifying heat pump water heaters

Uploaded: Jan 17, 2021

There is a surprising amount of water heater inertia in our area -- we are clinging to old-style heaters. I’ve been scratching my head about it. Mid-peninsula residents have been quick to adopt all kinds of clean tech, like EVs, solar panels, smart thermostats, LED lights, and more. We care about climate change and we want to do our part, especially when it involves cool new technology and some beefy incentives.

We’ve got all that going on with new-style water heaters, yet adoption is lagging. Heat pump water heaters greatly reduce emissions while using 3.5-6 times less energy than gas water heaters, but still we persist in firing up the gas to heat our water, boosting our home’s carbon footprint by about 50%. (1) What’s up with that?

Flame under a gas-tank water heater

This is the first in a two-part series about heat pump water heaters, which I hope will help answer that question, demystify the heaters some, and encourage more of us to give them a good look. In this first part, we are going to go on a virtual tour of some real life local installations after a brief overview.

Below is a picture of two Rheem water heaters. They look pretty similar, but the one on the left hooks up to gas and works like a gas stove, while the one on the right plugs into the wall and works like a refrigerator (in reverse). From this description, it’s hard to imagine that we’d care so much about which one we got that we’d choose the one that’s much, much worse for the climate (on the left).

A gas-powered tank (L) and an electric heat pump (R), images courtesy of Home Depot

They look about the same. They’re about the same size. And they’re both available at Home Depot. The one on the right is much more expensive, but there's a hefty local rebate and the bills are a little lower (2).

I asked some people who understand these water heaters why there seems to be a lot more interest in EVs than in heat pumps. I got a really interesting range of answers.

1. They are invisible. Since people can’t see these, unlike EVs and solar roofs, it’s hard to know who else has one, how “normal” they are, and if your friends and neighbors are buying them. People don't talk much about their water heaters, so it's hard to learn about them.

2. They are invisible. A different take on their invisibility is that since people can’t see them, there is less social pressure to get one, to show your friends that you aren’t burning gas for your showers. You can’t “virtue signal” with a water heater.

3. The installers are the problem. The “influencers”, the installers, contractors, architects, and builders, are conservative, with a “Go with what you know” attitude. Josie Gaillard, an Environmental Quality Commissioner in Menlo Park, estimates that “80% of installers will try to talk you out of it.” We certainly don’t see that with EV sales.

4. The installers are the problem. An informed take on the reason for installer pushback is that there are few qualified installers. Zach Liske, who owns a company that represents clean energy product manufacturers, said installation is “the bane of the industry. There are few trained installers. Our culture dissuades young people from going into the trades, and the diminished unions aren’t doing any training. So techs aren’t trained and there’s no place for training.” (His company, Flow Tech, is helping to fix that.)

5. Electric work is needed. Most heat pump water heaters need a 240V circuit and possibly other electrical work, though it can be reduced with the right choices. This means that the fuel switching can take longer and cost more to install. Update (July 2022): Rheem now has two 120-volt models available.

Interestingly, I heard a pretty different list when I talked with people who aren’t particularly familiar with these water heaters. They echoed questions about cost, but also raised concerns about placement and noise. I am going to address placement and noise below, and cost in a follow-up blog. For now I’ll just say that these need not be major obstacles in most cases. The trick is to find a qualified installer and minimize your electrical work.

A Virtual Tour of Heat Pump Water Heaters

Before delving into more tips and pointers, I want you to see what they look like in our homes, how they have been installed..

Some installations look like this one in Barron Park, where the heat pump water heater replaced a gas water heater in a small closet. In this particular case, a garage had been converted to a family room years ago, and space for the gas tank water heater was carved off in a small closet.

50 gallon heat pump water heater in exterior closet

The main elements of the water heater are shown in the annotated photo below.

The heat pump draws in air, extracts the heat (with the help of a refrigerant) to warm the water, and blows out cooler air. You can see in this installation that the air intake is drawn from the attic (A), where the air is generally warmer than it is outside. That makes the heat pump more efficient. The cooler air that is emitted leaves through a small vent in the closet door (D).

You can also see that the top portion of the appliance holds the heat pump and the bottom part holds the water (C). The hot water floats on top of the cold water, so the pipe carrying hot water out leaves from the top of the water area (B), and the cold water coming in enters at the bottom (I). This allows a user to draw hot water from the tank even when all the water is not yet hot.

A few additional lines leaving from the tank include a condensation line (G) and a relief valve line (H). The water heater needs to be placed somewhere where these can drain (in this case through the exterior wall).

You can listen to the sound that this tank makes here. The heat pump is turned off towards the end of the 15-second clip, so you can hear the difference. It is a low, steady sound, something like a microwave might make. This heat pump is rated at 49 decibels. It is located adjacent to a room where the homeowners like to listen to music and watch TV. The wall is not insulated (it is actually a hollow door that separates the two), and they could hear the hum inside, sounding like one of the speakers might be on. So they adjusted the schedule of the heater so it didn’t go on in the evening when they are in that room.

Below is a picture of a similar installation, this one in Midtown.

80 gallon heat pump water heater installed in exterior closet

In this case, both the air inflow and outflow are through louvres in the door and adjacent exterior wall (not shown). I asked the homeowner if she had adjusted the schedule, and she confessed that she hadn’t even downloaded the app. “It just works” was her overall impression. She said that if she listened for the hum she could hear it inside, but it was really not noticeable (unlike the wine refrigerator they had installed…). She also mentioned that her family of four, with two teenage boys, never runs out of hot water. In fact, at one point they had five houseguests and they still did not run out of hot water, though they were thoughtful when planning their showers. This installation has an 80-gallon tank. (BTW, can you see one oversight in this installation that would make it more efficient?)

Other installations I looked at had the heat pumps in the garage. Below are a few examples. The older model on the left has water inflow and outflow from the top of the tank. The middle one is a more complicated setup due to a solar hot water installation. The one on the right has been in some real-world tours, as you can see from the signs!

50 gallon heat pump water heaters of various vintages installed in garages

Two of the homeowners mentioned that their garage is cooler when the heat pump is running, which can be great in the summer and less great in the winter if you are working in your garage. You can hear the sound of the middle pump and the right pump. (We were not able to turn off the pump in that first video.) The GeoSpring heat pump on the left is the loudest of the three and is the oldest model, though good wall insulation meant it was not noticeable inside.

Tips from Heat Pump Water Heater Installers

As far as I can tell, the installations are pretty straight-forward. You need access to a 240v circuit and a place for drainage. If the heat pump is located near a sound-sensitive space, the homeowner can set a schedule or add some insulation or soundproofing to the adjacent wall. Maintenance is minimal, with an easy-to-access air filter that could be cleaned out every year or so. And the garage or utility closet feels safer with one less gas appliance. The most important tips that I heard from installers were:

- Plan ahead. Some installations cannot be done in a matter of hours. A 240V circuit with adequate current is sometimes easy to set up but sometimes more involved. Finding a good space for the heater can take some time if you currently have a tankless version. Home Depot or your contractor may not have the heat pump heater that you want, since these are still relatively new. Look into replacing your water heater before it fails, for example when it is 8-10 years old. Or at least set up the appropriate circuitry. The longest lead time (and expense) happens if you need to upgrade your electrical panel. That can take months, but fortunately it is rarely necessary, especially with newer low-powered options.

- Choose a model that uses only 15 amps. This will make it easier for the heat pump water heater to fit into your electric panel. There is almost no downside to the 15-amp models. Menlo Park Environmental Quality Commissioner Tom Kabat insists “California should just outlaw the 30 amp models.” Kabat has developed considerable skill in finding room in electric panels. You can learn more about his tips in this video. You can also download Kabat’s “Watt Diet Calculator” spreadsheet. (3)

- Consider a 120-volt model. If you live in a temperate climate, one of Rheem's two new 120-volt models might make sense for you. These significantly reduce the electrical installation work needed. One model works with any standard electrical outlet, and one requires a dedicated 120-volt 15-amp circuit. They may take longer to refill than the 240-volt models but to mitigate that, one model has an extra large compressor for faster refill speed, and the other (Hydroboost) model has a mixing valve (see below) to reduce the emptying rate. Review the specs to see if one of these is a good fit for you.

- Choose a larger size than you might normally choose. Since heat pump water heaters warm water more slowly than a gas-fired water tank, additional gallons can serve as a buffer.

- Consider installing a mixing valve. This allows you to heat your water to higher temperatures and then mix the extra-hot water with cold on the way out, effectively increasing the size of your tank. (4) It also allows you to schedule the tank to run during cheap electricity hours and then have it idle during the more expensive hours, though in practice the hot water won’t lose much heat over the expensive period anyway.

Installers, Rebates, and Costs

You can find plenty of information from your local utility about heat pump water heaters and rebates:
- Silicon Valley Clean Energy has a helpful guide linked from their webpage. They offer a $2000 rebate to replace a gas heater, plus an additional $1500 if you need to upgrade your panel.
- Peninsula Clean Energy’s webpage is here. They offer a $2500 rebate (you need to use a BayRen-approved contractor), plus an additional $750-$1500 if you need to upgrade your panel.
- The City of Palo Alto provides information here. They offer a $1200-$1500 rebate.

Silicon Valley Clean Energy has a terrific spreadsheet of installations that you can download to get an idea of contractors and prices. (I will discuss costs in more detail in the next blog post.) The Bay Area Regional Energy Network (BayREN) provides a list of qualified contractors, among other things. And the new SwitchIsOn initiative, from California’s Building Decarbonization Coalition, has information about rebates, contractors, and more for all kinds of electrification, including heat pump water heaters.

From what I have seen and learned, heat pumps are a terrific and simple alternative to gas fired water heaters. But in many cases they will cost $1000 more, even with the rebates. That is largely because of installation costs, including electrical work and permits. The homeowners I spoke with acknowledged the additional expense, but felt it was a relatively minor investment in exchange for decreasing their home’s emissions by 33% for all the years to come. A $1000 environmental donation might instead be diverted to a heat pump water heater installation this year. It’s not deductible, but it supports the burgeoning local clean energy industry while carving away at your home’s emissions. There is also an interesting new study from Nature Energy showing that heat pump heaters may in fact boost home sales prices. I will talk more about costs in the next blog post. See also my posts on price gouging and how to combat it and what to do if you get a noisy Rheem heat pump water heater.

I’d love to hear your questions about these appliances, or any other stories or tips you have to share. I’d like to give a special thank you to homeowners Bryna Chang, David Coale, Cedric de La Beaujardiere, Larry Reeves, and John Sack for taking the time to introduce me to their water heaters, with particular thanks to David Coale for arranging most of these visits.

Notes and References
1. Gas water heaters use about one-third of the gas in our homes, resulting in about one-third of our home’s carbon footprint.

2. The bills are much lower if you have your own solar power. Otherwise they are just “a little” lower. More on this in the next blog post.

3. I plan to do a post on electric panels at some point. They are increasingly important parts of our homes that we need to understand and either upgrade or adjust to fully electrify. More tools are becoming available to allow homeowners to make better use of their panels.

4. This mixing valve is required if the tank is used as a backup for solar hot water, since that water enters the tank very hot.

5. Nearly all of the homeowners I spoke with were using a Rheem heat pump water heater. You can find an informative brochure with some comparison information on the last page here. The City of Palo Alto has a spreadsheet with some comparison specs here. SVCE’s “Appliance Assistant” for heat pump water heaters is here. There is also a lot of good information on CleanTechnica, though the page is several years old.

Current Climate Data (December 2020)
Global impacts, US impacts, CO2 metric, Climate dashboard (updated annually)

This map from NOAA shows how much warmer the year 2020 was than the 20th century average. See here for more information. This is why we need efficient electric heat in our homes.

Comment Guidelines
I hope that your contributions will be an important part of this blog. To keep the discussion productive, please adhere to these guidelines or your comment may be moderated:
- Avoid disrespectful, disparaging, snide, angry, or ad hominem comments.
- Stay fact-based and refer to reputable sources.
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What is it worth to you?


Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 17, 2021 at 8:46 am

Sherry Listgarten is a registered user.

BTW, here is a comment that was emailed to me, regarding the need to plan ahead.

I would underscore the to-do list the installers suggest: "plan ahead". Basically, I knew my gas WH had about 4 years of life left two years ago, so I started the research process, and then found the brand and a then-current model and read its specs to be sure it would fit. I had the electrical work done ahead of time to pull a line to where the WH was, and I picked out a model and an installer who was on the city's list and got a proposal/price. I checked the rebate stats. All this can be done so you can time the work so it isn't an emergency replacement. Take your time, but plan ahead. And, as you said, it took about two months for the actual WH to arrive.

Posted by marc665, a resident of Midtown,
on Jan 17, 2021 at 7:33 pm

marc665 is a registered user.

What are you going to do in the next few years when we have rolling power outages and the state mandates restricted use of electricity between 4 and 10 pm every day?


Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 17, 2021 at 9:30 pm

Sherry Listgarten is a registered user.

Hey Marc. That's a great question, thanks. I hope people answer with their perspective, but I can at least answer for me.

1. I can't wait for time-of-use rates. I can keep most high-power activities out of 4-10pm (car charging, house heating, water heating, clothes drying), so I expect my electric bills to go down. (Those appliances often come with built-in schedulers.) The stove and oven I'd still use in the expensive window.

FWIW, our heat already doesn't come on in the evenings because the house is well insulated. I generally think it's a good idea to insulate before going to electric heat.

2. Power outages are a bummer, though our gas boiler already doesn't work when the power is out. It needs electricity, as do most gas heaters. I've never missed it. I mostly miss lights and internet when the power goes out. Rolling outages are designed to last 1-2 hours, so I don't worry about those at all. I'd worry more about a 12+-hour outage, but those are fortunately exceedingly rare in this area.

If I lived in Santa Rosa, I'd worry about the power shutoffs. Those can last days. If I did live somewhere where I could expect the power to go out for several days at a time, a few times a year, I'd probably get solar and a battery. The battery is expensive, but I'm not sure how to electrify without that in those places. You could probably argue that Santa Rosa residents should get big discounts from PG&E and/or the state on home batteries.

Posted by Joseph E. Davis, a resident of Woodside: Emerald Hills,
on Jan 17, 2021 at 9:52 pm

Joseph E. Davis is a registered user.

I'd be reluctant to switch any major appliance from gas to electric because our electric bill is already very expensive. Any incremental use of electricity will be at the top end of our high tiered rates.

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 17, 2021 at 10:26 pm

Sherry Listgarten is a registered user.

Joseph, as you can imagine, there's been a ton of work done on the economics of electrification. I'll cover some of it in my next post. It's important to keep in mind that these electric heat pump appliances are much more efficient than gas ones, and "smart" to take advantage of time-of-use rates, so bills are often much lower than you would think. I also expect we will see rates evolve. Did you know that Texas has plans with free electricity at night?

BTW, if your electric bill is really expensive, read this post! It's super easy and fun to figure out where you are using electricity, and there are lots of ways to get your bill way down. As a very nice and important side-effect, it'd be a good win for the planet.

Posted by Joseph E. Davis, a resident of Woodside: Emerald Hills,
on Jan 18, 2021 at 9:57 am

Joseph E. Davis is a registered user.

Sherry, I read your post, but I would not call that "super easy". It sounds like a research project of moderate difficulty and coincident impact on the household (which is shut in and grumpy to start with). The research project would trigger an unknown number of upgrade projects with their own costs and overhead.

If we want people to switch to electricity, we need to make electricity cheaper.

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 18, 2021 at 12:17 pm

Sherry Listgarten is a registered user.

Joseph, I hear you, and I'm sorry if I downplayed what it takes to understand a home's electrical use. FWIW, one approach might be just to read your meter at some version of: 7am, noon, 5pm, 10pm. If you do that for a few days, you'll learn a lot by seeing (a) when electricity is used, and (b) how much it varies on different days. You might be able to make some good guesses just from that.

To your main point, I agree 100% that cheaper electricity would make it easier to switch. Thanks for your comment!

Posted by KOhlson, a resident of Old Palo Alto,
on Jan 18, 2021 at 12:17 pm

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Great post - very informative. I look forward to part 2.
Dec/Jan/Feb are peak months for our CPA Utilities bills. And every year when I review them during this time, I am again reminded how complicated the bill is. It seems designed to obfuscate. Way too much unactionable information in there. Examples: There are 4 components to the electricity portion, and 6 to the gas. Why not a 13-month graph - compare December to December from the previous year - instead of 12?
I mention (rant?) about this because without knowing what's on the bill, and what I can affect, it's hard to make an informed decision moving forward.

Posted by pbb, a resident of Menlo Park: The Willows,
on Jan 18, 2021 at 1:31 pm

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I would be interested in a comparison with tankless water heaters, thanks!

Posted by West Menlo Mom, a resident of Menlo Park: University Heights,
on Jan 18, 2021 at 4:00 pm

West Menlo Mom is a registered user.

Nice work - thanks!

Posted by Alan, a resident of Menlo Park: Belle Haven,
on Jan 18, 2021 at 5:55 pm

Alan is a registered user.

You did touch on one downside of hybrid heat pump water heaters - apparently, they are slower to warm the water, so use a bigger tank. Is there any substance to the following (claimed) concerns?

1) Hybrid heat pump water heaters are less reliable (are they really?);
2) In winter, hybrid heat pump water heaters are not only slower to heat water, they sometimes can't reach the target temperature.

We have our water heater in our garage. I suspect - living in Menlo Park - (2) is not so much of an issue - but it might be a real problem in a garage in Winnepeg. I sometimes wondered if it would have a slight cooling effect on our garage, as a bonus. While anything would help on some summer days, is it noticeable?

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 18, 2021 at 9:00 pm

Sherry Listgarten is a registered user.

@KOhlson: If your electric bill looks like mine (it sounds like it does), then you can affect virtually all of it. Same for gas. The rates are explained here. AFAICT, the only charges independent of use are the gas "monthly service charge" and the tiny electric "state energy surcharge".

FWIW, my bill does show a comparison with last year. The graphs have dark bars for the past year, and then one white bar showing the same month a year ago. (This is on the second page.) Check again? If you have questions, just call the utility, I expect they'd be happy to help.

@pbb: Great question. Tankless heaters have a somewhat better emissions profile than tank heaters and are somewhat more costly. So it's an easier economic comparison with heat pumps, and still a big emissions win. Not the same shape, though, so it may be harder to place the heat pump.

One very interesting thing I learned about tankless water heaters is they leak methane each time they go on and off, which is pretty often. That worsens their overall emissions rates. I did a blog post on it a while ago, complete with videos. Check them out! More up-to-date is this article, which talks about the paper the team wrote and the suggestions they have for reducing the leaks. Basically, if you don't want hot/warm water, then you want to turn the tap to cold before turning the water on, rather than turning it on and then switching to cold.

@Alan: I haven't heard any reliability concerns. Heat pumps are not particularly new technology. Maybe the reference was to power outages? (See above.)

Our climate is perfectly suited to them, but they are getting better each year for cold climates. Here's some more info.

Re speed, they don't heat up all that slowly. See the "first hour rating" (for example on the last page of this brochure. (The 15-amp versions heat more slowly than the 30-amp.) Most heat pumps also come with an option to switch to faster (and more expensive) electric resistance heating if you need it. (Some experimental heat pumps that require only a standard (120v) outlet do not have resistance heating.)

Finally, yeah, if you put it in the garage, it would cool the garage and would be noticeable at least when close by. Here's a comment from someone who installed one in Hawaii: "The heat-pump water heater in our Kauai condo kept the water heater closet deliciously cool all year even though it had a louvered laundry closet door. Sometimes I would go stand in the water heater/laundry closet to cool off! The dry air is a nice benefit almost anywhere."

Posted by Tom, a resident of Menlo Park,
on Jan 18, 2021 at 10:12 pm

Tom is a registered user.

@pbb Another comparison of heat pump tank water heaters vs. gas tankless water heaters is resilience.

In a 12 hour power outage, I have a 50+ gallon tank of piping hot water to enjoy, but my tankless gas neighbor has none. He cant get his electronic ignition and combustion fan to function, so no hot water for him.

In a gas outage after a quake, the power comes back on "quickly" but it takes days for the gas to return. PG&E goes house to house checking for dangerous gas leaks before turning on gas. But with my tank of already hot water I might not even run out of hot water if the power outage was under 12 hours.

After a quake that's more severe, I have a 50+ gallon tank of tap water strapped to my wall and my neighbor has a half gallon of water in his tankless water heater.

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 19, 2021 at 11:28 pm

Sherry Listgarten is a registered user.

A reader wrote in asking: “How do they figure water heaters are 30% of our gas use? When I look at my bills, my gas usage in the summer is so low, and includes water, stove, and dryer, that I can’t imagine my yearly average is 30% of my total gas use.”

It’s a great question. I had the same one! One thing to keep in mind is that you use hot water year-round but hot air only (say) five months. Plus gas prices are more expensive in winter, which makes your bills even higher when the heat is on. This means that even if your winter bills are much higher than your summer bills, your water heater can still be one third of your gas use on an annual basis. (I’m ignoring dryers and cooking for now, which are typically much smaller.)

As one example:

Suppose w is how much gas you use for hot water, on average, per month.
Suppose a is how much gas you use for hot air, on average, per cold month.
Say the heat is on five months of the year.
The claim is that, on an annual basis, hot air use (5 * a) is only twice the hot water use (12 * w).
That is, 5a = 2 * 12w, so a = 4.8w. So the claim is true (a third of our gas use is from hot water) even if we use almost five times as much gas for hot air as for hot water during the cold months.

But that’s not all. The amount of gas we use for heating in one winter month is a + w = 5.8 w. The amount of gas we use in one summer month is w (we only heat hot water). With higher rates in winter, our winter bill will be at least 6 times our summer bill.

That is true even though the total gas use for hot water is big, half of what we use for hot air (on an annual basis).

This simple analysis ignores cooking and drying, as well as fixed costs on the bill. But you get the idea. Since hot water is used year-round, it adds up.

Even then, it may not make economic sense to invest in a heat pump water heater. We’ll talk more about that in the next blog post. But hot water is a surprisingly big source of home emissions. Thanks for the great question!

Posted by Suzanne, a resident of another community,
on Jan 20, 2021 at 11:25 am

Suzanne is a registered user.

Just wanted to mention that we've had excellent experiences with our two heat pump water heaters. Because of the layout of our house, there is a HPWH of the type in your photos that serves the kitchen and laundry at one end of the house, and another heat pump water heater at the other end serving the bathrooms and showers. The unit serving our showers is a split system �" the equipment that does all the work is about the size of a suitcase and sits on a pad outside, looking and sounding like a small air conditioning unit; it sends hot water to an 80 gallon tank that just holds the water. This system cranks out the hot water �" our family of 4, including teenage girls who take showers that are longer than I'd like them to be, has never run out of hot water, even when all 4 of us get home from camping trips, running 2 showers simultaneously, and another 2 right after that. And the 80 gallons of hot water provided a wonderfully warm shower a full 24 hours into our last Public Safety Power Shutoff (while our neighbors with tankless water heaters had no hot water.)

Posted by Mondoman, a resident of Green Acres,
on Jan 20, 2021 at 9:38 pm

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Thank you very much for covering this topic! My knowledge is mostly from Seattle, where many(most?) water heaters are electric resistive (conventional), whether with tank or tankless. Capital cost is low and reliability is high because of the lack of moving parts. However, with Seattle's electricity prices having almost tripled(!) in the last 20 years, pumping heat rather than creating it from electricity is naturally getting more attractive.
Regarding reliability, I suspect the earlier poster was just pointing out that heat pump water heaters have moving parts, noxious liquids under pressure and other reliability-reducing features in addition to the features of standard electric resistive water heaters. In this early stage of development of heat pump heaters, manufacturer reputation for design and build quality matter a lot.

Posted by Tom, a resident of Menlo Park,
on Jan 20, 2021 at 11:44 pm

Tom is a registered user.

@Mondoman, I was thinking a similar thing when I first got my hybrid heat pump water heater (aka heat pump water heater) 5 years ago that looks like the leftmost of the three in the last picture set. They call them hybrids because they also have simple electric resistor backup heating elements. If there was a problem with the refrigerant heat pump system, I would just flip the switch to resistor mode.
I asked a Rheem factory rep about the longevity and he assured me the tank will go out first before the heat pump. So maybe I should replace the $20 anode rod at year 10 that protects the tank and try to make it past 20 years.

Posted by Mondoman, a resident of Green Acres,
on Jan 22, 2021 at 12:01 am

Mondoman is a registered user.

@Tom Yes, Rheem's a good company. Given the expense of the non-tank part, replacing the sacrificial anode makes good sense. I vaguely remember from some older This Old House show that it can really get stuck in place and may be better replaced every few years rather than waiting until it's so far gone that it isn't working anymore.

@Sherry You wrote that "It's important to keep in mind that electric appliances are much more efficient than gas ones,..." For resistive heating vs. combustion, my impression was that the opposite was often true. Modern furnaces and rangetops with gas burners can be very efficient, while power generation via combustion converted to electricity is not as efficient. Of course, non-standard electric technology like heat pumps and induction cooktops are certainly more efficient.

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 22, 2021 at 7:53 am

Sherry Listgarten is a registered user.

@Mondoman: Yes, you are right. I fixed it to be more specific.

Posted by Jan Buck, a resident of another community,
on Jan 22, 2021 at 12:48 pm

Jan Buck is a registered user.

Do you think that the insulting jackets for gas hot water heaters help the gas bill? They are reasonably priced.

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Jan 22, 2021 at 2:28 pm

Sherry Listgarten is a registered user.

@Jan, I had the same question! What I read was that modern hot water tanks are normally well insulated on their own and they don't benefit from a blanket. They suggested touching the tank and, if it seems warm, then go for an insulating jacket. I touched ours, which was installed 5-6 years ago, and it was not warm. See what you find!

Posted by Thank You!, a resident of Duveneck/St. Francis,
on Jan 24, 2021 at 12:16 pm

Thank You! is a registered user.

Fantastic article. I was just researching heat pump water heaters yesterday and this article is so much more informative. I particularly like the sound recordings, discounts available and advice about preparing ahead. My biggest concerns with heat pump water heaters are maintenance and sound and I would get a hybrid. I'm also interested in getting solar when we replace our roof in a few years and Tesla's powerwall. I'm definitely going to follow you from now on. Thank you and about to read your next article on this subject.

Posted by Scott, a resident of Community Center,
on Feb 15, 2021 at 4:49 pm

Scott is a registered user.

Thank you for this post. I am interested in a "hybrid," but wonder if the cumulative challenges make it a good choice (I realize these vary by household). Mine: 1) maybe the panel; 2) no good drainage option, so an added pump would be needed, increasing cost (and noise?); 3) my basement is only slightly warmer than ambient air...yes, it is rarely if every lower than 40 degrees F, but if for many winter nights it is in the, say, 45-50 degree range, how efficient will the heat pump be? 4) My house is already cool-ish from this cool basement; how much cooler will it be from pumping cool air into it?
I'm left puzzled about the straight electric option--rather than "hybrid"...I feel the post doesn't compare the two.

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Feb 16, 2021 at 9:56 am

Sherry Listgarten is a registered user.

@Scott: Great questions, and you are right, this post doesn’t compare this type of water heater with other electric water heaters, such as electric resistance tank, electric resistance tankless, or split air-to-water heat pump.

If your electric panel may be a concern with a hybrid heat pump water heater, then that definitely rules out electric tankless, which use a crazy amount of amperage (80+).

An electric tank will work fine, but will use more energy. How much more? Heat pump water heater efficiency is measured when ambient temp is 65-70. I’ve seen a chart for another heat pump that suggests that efficiency would be about 20% lower at an air temperature of 45-50, which would put your basement heater still around 3x more efficient than an electric resistance (.8*3.6/0.93).

As you know, the hybrid has electric resistance built in (more if you get the 30-amp than the 15-amp), and has settings that let you specify very coarsely how much of the resistance you want it to use. That could adjust the coolness and noise under the house some (more resistance heating means higher cost but less coolness and noise assuming the heat pump doesn’t run when resistance is on).

The split air-to-water heat pump, as made by Sanden, is another option. It’s much more expensive but much more powerful. The heat pump would be quieter I think than the integrated ones because the fan would run at lower speeds. You could also put it outside of the house if you wanted, and just have the tank under the house. Then the basement wouldn’t get cool, and the heat pump would benefit from warmer temps during much of the year. It’s much more expensive, though.

How cool the basement gets with all these options depends on how much water you are heating, how big your basement is, how well ventilated it is, etc. I would guess you wouldn’t notice the somewhat cooler basement in the house, but it’s just a guess.

Hope this helps some.

Posted by Sherry Listgarten, a Palo Alto Online blogger,
on Feb 17, 2021 at 9:30 am

Sherry Listgarten is a registered user.

I forgot to add that the Rheem one-piece heat pump water heaters come with a duct kit, so you could feed warmer air into the heat pump if you want.

Posted by Kopernikas Green, a resident of Laurel School,
on Mar 4, 2021 at 6:50 am

Kopernikas Green is a registered user.

When the concept for heat pump was first proposed, wasn't it dismissed as some sort of a sham, or something that we didn't understand? After all, there's no such thing as "free energy". But the way that I will explain this to my little son (when he's old enough to use his own blower door) is the pretty simple situation of a cooler with cans of soda and ice in it. The water is the refrigerant, and it goes through a phase change, just like in a heat pump. We do the work to take ice from the freezer and put it into the cooler. It absorbs heat and changes phase and melts. Then we do the work to take the meltwater and put it back in the freezer. It gives off heat and changes phase and freezes. Then we can put it back in the cooler, and repeat again and again and again. In the winter up North you could use the outside as the refrigerator for "free cooling". I wonder if this is a relatable way to describe the concept.

Posted by MrScott, a resident of another community,
on Mar 28, 2021 at 3:37 pm

MrScott is a registered user.

I'm in the Seattle area. Considering adding one to our hydronic heating system, however one big question is where would it pump heat from?
For air source, indoors is heated by the propane-fired boiler, so robbing Peter to pay Paul.
Outdoors is coldest when we most need the heat.
Ground source (geothermal) requires trenches or other means of installing a ground loop to pull heat from the ground ($$$$$), and we don't have an obvious good place to do that on our property.

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