Switching to a Heat Pump Water Heater

Drip, drip, our water heater started leaking. I considered three replacement options:

  1. A gas tank water heater for $2500, the standard emergency replacement. It’s so common that the plumbers have those units “on the back of a truck” and can install it in hours.
  2. A tankless gas water heater for $5000, the standard upsell from the plumber. At least one plumber had that “on the back of the truck”, too.
  3. A Heat Pump Water Heater (HPWH) for $4000. They are the future, but plumbers were surprisingly ignorant about it. The cost breakdown is $5200 for the appliance and plumbing plus $800 for electric work minus $2000 incentives.

I really didn’t want to purchase another fossil fuel burning appliance, so I focused on the heat pump. A discussion of of the other options is at the end.

Call to Action: If your gas operated water heater is older than 20 years, consider replacing it with an hybrid electric Heat Pump Water Heater! Start Here.

What is a Heat Pump Water Heater (HPWH)

You already have a heat pump operating in your fridge. A heat pump moves heat from one place (the inside of the fridge) to another place (the outside of the fridge). We use this technology to move heat from the outside of the water heater to the inside of the water tank. A heat pump water heater is a “reverse fridge “.

The main benefit is their extreme efficiency. For every unit of energy you put in, we get 5 units of heat in the water! This doesn’t violate the physics principles you learned in high school, as the heat comes from the surrounding air, not from the electricity. We only need electricity to move the heat. As a side effect, the surrounding air gets cooled, which is a feature in summer.

The main disadvantage of a heat pump is that water heating takes a lot longer than using an open gas flame. That’s why there is a tank. We heat the tank for an hour and then are ready for showers.

The water heaters are also called hybrid electric, because they still have a traditional electric heating elements, similar to an electric tea kettle. It’s used when you use more hot water than the heat pump alone can provide. The element can be turned off if desired.

With gas, it matters not when you use it, but with electricity, some hours of the day are better, cleaner, and often cheaper than others. The heat pump water heater heats water when electricity is cheap/clean, and you can use the hot water when needed. It’s the ideal solution if you worry about global warming, and it provides all the conveniences of a gas alternative. It is strictly better in almost all aspects. Where is the catch?

First, there is price. A heat pump will be more expensive than a simple gas fueled tank heater. It will be about the same cost as a tankless heater. The heat pump may also require additional electric work. Your electricity provider may have incentives to cover part of the cost.

Second, there is noise. The compressor will sound similar to a fridge or a small AC unit. It’s not something you want in the corner of your kitchen.

Finally, there is longevity. Heat pumps have moving parts and a tank. Because of those they will likely fail sooner than a tankless water heater who has neither.

The Project

Luckily I noticed the leak early, and after a panicked first night, every plumber gave the tank at least another few days, maybe weeks, before the big flood. So we had time to do the right thing.


The heat pump part doesn’t take much electricity, but the electrical heater element uses a lot, and thus required a new electric circuit (240V/30A). While our city has quick permits for say a new (240V/60A) circuit for an EV charger and self-service permits for water heaters, this was a completely different situation, and required a regular construction permit, which complicated and slow. It’s interesting that the city requires all new construction to have electric water heaters but replacing one in an existing building faces additional bureaucracy. It took me many hours of work to generate the documents for the permit, and work with the city to get it approved after many, many days.

Update: The inspection was quick and easy. The inspector suggested wrapping the short segment of hot water piping into insulation, but was otherwise happy.


The extra electric circuit makes things more than twice as complicated. You need either a general contractor or two licensed contractors, which makes you the general contractor. The State of CA has a scary memo about why you should not do the latter, but the one general contractor I found was busy for longer than I expected my old water heater to survive. So I coordinated two different firms.

Brands and Models

I spent another few days doing research and interviewing contractors to figure out which model to install. There is basically no information available beyond manufacturer spec sheets. The few options I looked at include

  • Rheem/Ruud (same appliance sold under two brands)
    In particular a Ruud Professional Ultra Hybrid Electric Water Heater PROUH80 T2 RU375-30 and a Rheem Professional Prestige ProTerra Hybrid Electric Water Heater PROPH80 T2 RH375-30.
    I ended up going with Rheem/Ruud because they seemed to have the smartest heat pump. It came with an app that despite a 1.6 star rating at least exists. You can also have the heat pump remote controlled by third parties, e.g. OhmConnect, who give you money if they can turn it off at peak hours. The main concern were a lot of reports of too much noise on the Internet. I decided to take the risk on that one.
    I got the Ruud over the Rheem, because it’s the brand the contractor works with.
  • AO Smith/Bradford White.
    In particular a Bradford White Aerotherm RE2H80T10 and a AO Smith Voltex® Hybrid Electric Heat Pump Water Heater HPTU-80N
    Both seem to be equivalent. Nobody complained about their noise, but they didn’t claim they were quiet either. AO Smith advertises some smarts, but it’s not clear if this is even functional. Both seem stuck in pre-Internet times.
  • Stiebel Eltron
    German quality, awesome looking, but not as efficient (surprisingly) and not clear it’s quieter or has smarts. Also while I love German engineering, I also prefer somewhat locally made products. No contractor brought it up either.

The quotes for appliance and installation are all over the board, from 5k to 10k. The units are all huge and require 3 people to carry in, instead of two. If you can get away with smaller units, (50g tanks instead of 75g or more) quotes will be lower.

First Results

The first day it was using so much electricity and making so much noise, that I started doubting my decisions, but once the tank was hot, and I figured out how to set the correct modes, it got a lot less demanding.

The humungous Heat Pump Water Heater. It’s an 80g tank with a heat pump on top.

The heat pump is installed in the garage, and as a side effect cools down the garage. This has been very convenient during hot summer days. I’ll find out what happens in winter.

The panel on the appliance requires a ladder to operate. The heat pump has multiple modes, using only the heat pump, only the electrical element, both in an energy saving way, or both in a high-demand way. It also has a vacation mode.

The smarts are adequate. You install the Ecosmart app and connect to the device’s Wifi server to configure the device to connect to your home Wifi. Once this is achieved, the app becomes a convenient remote and you no longer need the panel and the ladder.

In the app, you can change schedule changes 4 times each week day. You can turn it on at midnight to use cheap electricity and the heat pump only to get back up to say 125F, then at 7am switch it to Energy Saver which will turn on the electrical element if required while people take morning showers. Turn it back to only heat pump at 9am, and turn it completely off at 3pm when the cost of electricity goes up. You can have different timings on week-ends. These current settings also mean that the pump makes no noise between 3pm and midnight, so it doesn’t bother us in the evenings.

If that’s all too much, just set it to Energy Saver or Heat Pump mode and forget about it.

You can also connect the heat pump to other third party services and even a Raspberry Pi, if that’s the way you want to go.

The smarts panel. The key is connectivity and remote control.

The noise is more than I wish, and less than I feared. It runs at about 65db (1 ft away). The compressor can be heard through half the house if it’s otherwise quiet. But it’s the sound of clean energy, so I think I can live with it. If it ever bothers me, I will turn it off for a while, or switch it to electric only mode and it will still be better than gas. At the next scheduled event, it will go back to the regular program.

Measuring 63db 16″ away from the fan opening.

Six Months Update

Summer: Turns out the cooling effect is not as great as expected. It does cool the garage, but it does this when electricity is cheap and before we need water in the morning, which means at night. The hottest time of the day is also the most expensive, so it doesn’t really run then. If I i need the garage and think about it, I run it 2pm-3pm, though.

“Winter”: Where I live “winter” is 32F on a few cold mornings. It’s cold in the garage, but not by much. You can see how the temperature of the house and the garage start dropping in the evening. At 3am the heat pump kicks in to get ready for the morning demands of hot water. It’s normally done around 6am, at which point the garage starts to warm up a bit again, likely due to leaked heat from the furnace. Outside, the low was 32F, the garage went down to 42F. Without the heat pump, it might have dropped to 45F, maybe. Both are too cold to hang around.

If you wonder what happened at 10am, that’s when I started a cardio workout. Humidity increased drastically.

Heat pump in the garage during “winter”


For now I am still quite happy with the outcome of this project. I can only recommend it. Due to the long lead time of permits, and the extra work of adding another electric circuit, this is not a home improvement you can do after your old water heater bursts. You need to plan it ahead, and possibly do it before the final breath of your old water heater.

The other options

Gas instead of coal or oil was a good idea a century ago (and still is), but in the face of global warming even gas is polluting. While gas appliances are pretty safe, they still lead to the occasional fire, and are not ideal in earthquake country. In many communities, including our town, they can no longer be installed in new construction. But you can still replace an existing gas heater with a new gas heater, and gas remains the bread and butter of the emergency plumbers. In our town it’s also trivial to get a permit to replace a gas water heater with a gas water heater, so that can be done quickly.

A gas fueled tank is the worst solution in most cases, as you are basically burning gas to keep the tank hot, whether you need it or not. Also, most tanks start leaking around 20 years.

Tankless heaters are normally a lot more efficient as they only heat on demand. They have no moving parts and no rusting tank, which should greatly increase the life span of the appliance. In our house we have recirculating pipes to make sure hot water is available quickly at any faucet. Those pipes saves water, but increases energy use. In this situation, the tankless heater would still kick in every half hour or so to replace the lukewarm water in the pipes with new hot water.

Tankless electric heating has a lot of benefits, especially if you heat right at the faucet. They have no moving parts, and no tank, so they should last a very long time. The main problem is that they will require electricity when you need the hot water, and being able to time-shift energy use is crucial with electricity for environmental and economic reasons. The time-shift could be achieved with a whole house battery. It may be the preferred solution for new construction. You would only need cold water distribution to the taps!

In an existing house, it would have been a bigger project, as I need higher capacity electric circuits near all the bathrooms, and room to put these heaters. A central tankless electric heater solves some of this, at the cost of heating the recirculating pipes, but lacking a house battery, still suffers from electricity needs at peak time.

Last Updated on January 3, 2022.