E-mail Sherry Listgarten About this blog: Climate change, despite its outsized impact on the planet, is still an abstract concept to many of us. That needs to change. My hope is that readers of this blog will develop a better understanding of how our climate is evolving a...  (More) About this blog: Climate change, despite its outsized impact on the planet, is still an abstract concept to many of us. That needs to change. My hope is that readers of this blog will develop a better understanding of how our climate is evolving and how they want to respond, and will feel comfortable asking questions and exchanging comments on the topic. It is important that we develop a shared understanding of the basic science and impacts of climate change, to make sense of our actions and policy options going forward. My background is not in climate science, and I'm not even particularly green; my hope is that helps to make this blog more relatable. I studied math and neurobiology on the east coast before moving out here in 1987 for grad school in computer science. After working in the tech industry for about 25 years, I retired a few years ago to better align my time with my priorities. I love spending time outdoors, and feel deeply our responsibility to this incredible planet that we call home.  (Hide)

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Blogger's note: I have removed a comment from CyberVoter in Atherton because it contains several unsubstantiated and incorrect claims. CyberVoter, please feel free to republish with links. For example, you say that most people are paying more than $.45/kWh for electricity. Where do you get that information? You say that there are a number of things that would make a bigger difference than decarbonizing buildings, like stopping High Speed Rail. What are the projected net emissions from High Speed Rail, and how does that compare with building emissions, or even just residential water heater emissions? You say that a dog is as polluting as an SUV. Again, data? I hear your frustration about electrification and your concern about the growing demand. But I ask that assertions made in comments on this blog be grounded in facts and not in fears.

Great article. I'd like to add one additional point. The heat pump water heater (HPWH) takes heat out of the air and puts it into the water in the tank. The exhaust is cool air. In other words, the HPWH is also an air conditioner! Our HPWH has kept our garage cool all summer, and by not having a hot garage attached to the house, the house has stayed very cool as well. We installed a home air conditioner several years ago and we have yet to turn it on this summer. Our efficient HPWH is giving us the double benefit of hot water and a cool house.

That air conditioning benefit of a heat pump is a real bonus, who knew?! I really appreciate all this information re installation and features because I'm sold on heat pumps, and we will replace our old gassy heater with one as soon as it's feasible.

Thanks for this post. The next decarbonization project for our household is the water heater. The one after that is the furnace. Gotta get rid of that carbon!

I am the parent who hasn't given a second thought to our 65 gallon 30 amp HPWH installed in September 2021. It provides plenty of hot water when we need it. Rebates from BayRen and Peninsula Clean Energy totaled $2650 bringing the net cost to $4300. We haven't noticed a big impact on our electric bills, but maybe we ignore those too. Now that we have also installed a heat pump for space heating and gone fully electric, we have qualified for an increased tier 1 allowance from PG&E, so maybe I will start paying attention to those electric bills. Now that our 125 amp electric panel is maxed out, consideration of the 15 amp model HPWH might have been a good idea.

PG&E rates are significantly higher than City of Palo Alto electric rates, greatly extending the "payback period." Glad to hear the 15A plug-in version is now available. If your electricity is generated by burning gas your carbon reduction is not 100%. Much of the US electric supply comes from this source. Sunwork is truly a gem. Thanks for your article, I hope you continue enjoying your hpwh for many years to come.

Thanks for the great comments/questions. I also got a few in email, so I will address those here as well. Someone emailed me asking about whether a closet installation works. Yes, if well vented, per the installation instructions. It is also the case that you can get a HPWH with a duct kit, and in my case we ducted the output air into an adjacent large closet that has a refrigerator in it, figuring the cold air would help the refrigerator run more efficiently while also removing it from the intake. The HPWH closet gets air from outside (there is a vent) as well as from the garage. The large closet next door has two doors, both of which vent to the garage via gaps underneath the doors (cold air sinks). I will try to do a follow-up in the spring that covers efficiency of the appliance in winter. The closet installation shown below has a duct on the inlet, so that air from the adjacent garage enters the water heater. There is no duct on the outlet (the venting on the right of the tank), which is oriented towards some vents on an exterior wall. A tricky part about closet installations is getting the tank oriented properly so that the ducting and piping and condensation line all fit nicely and the keypad is easily accessible. Someone else emailed me this link with information about credits and rebates via the Inflation Reduction Act, pointing out that credits are available to all (not income-qualified), though they are capped at $2000 annually and may need to roll over if larger. This reader is excited to take advantage of Sunwork’s lower cost installation, a BayRen rebate, operational savings, and the tax credit. He lives in a condominium in Santa Clara and is sharing the information with his neighbors who want to reduce their gas use but may not understand their options. @Matt mentions the nice cooling effect in summer and a reader in email mentioned the dehumidifying effect, which can be nice in a basement. I did hear a homeowner say that in the winter it is less comfortable for him to do wood-working in the garage when his HPWH is running, though it is more comfortable in the summer. @Sam, I agree that with PG&E rates there isn’t much in the way of operational savings. So the rebates and tax credits will have to be enough. On the other hand, I just learned that Santa Clara has electricity rates of $0.12/kWh (!!). I would really like to see electric rates come down relative to gas in more places. Re the electricity supply, California’s was 52% emission-free in 2021 (renewable and nuclear and large hydro). The US was 39% emission-free. Those numbers are not bad, and getting better every year. Finally, yes, I agree that SunWork is a great organization. There are lots of opportunities to volunteer with them if people are interested. Thanks again for reading, and for the really informed and interesting comments.

Many houses in Palo Alto have detached garages or their garages have been converted to living space. For these older homes the water heater is often in the living space, sometimes in a closet. They do not come close to meeting the space requirements for a heatpump. These houses are not well suited to install a heat pump water heater. Also, the noise is much more impactful. Lastly, heat pump water heaters can be much more costly to install. I strongly support subsidies and even increasing the subsidy. However, I think its too soon to mandate that any house be required to only replace their water heater with a heat pump water heater.

Sherry - such an interesting (& detailed) article. Thank you. I have an older home with a basement, which is where my hot water heater is now. I gather from your comment to Matt that a basement location is doable? So interesting about the cooling effect. Thanks again.

I love my HPWH. We installed ours back in May 2021, and I can see my gas usage during the summer months dropped from 13-15 therms/month to 2-3 therms/month. That's what we use for cooking. The sound is not an issue - we also have a recirculating pump that turns on 2-3 times/day just like you Sherry. I hear a sound kind of like wind blowing when the heater is operating. The fact that it cools our garage while heating water is a bonus too. We paid $1700 for our heater from Home Depot, paid $1000 for installation and miscellaneous parts (I helped the installer a bit), $83 for the permit in Los Altos, so after our $2000 rebate from SVCE, ours only cost about $800 net! I'm looking forward to getting a heat pump home heating system to replace our gas water heater in the future.

@Bob: Yes, it is very common to put a HPWH in a basement. @Dean: Fantastic! I hope pricing like that becomes the norm soon. @Local: I agree that not every existing single-family home has an easy path to a HPWH right now, though I think most do. (Homes with tankless water heaters might be one example.) I would love if the city would pick 100 homes at random and analyze what it would take to install a HPWH so they can get a better idea of what the gaps are that need to be addressed and where they might mandate electric replacements with little downside. Ideally they'd already have that info from the Home Genie program, though I don't believe they did that analysis early on. (Not sure they do it now, for that matter.) For now, imo incentives for residents and contractors are the way to go for existing homes while we build the workforce and evolve the tech, and fortunately we now have help from the federal government in that vein!

@Sherry "I would love if the city would pick 100 homes at random and analyze what it would take to install a HPWH so they can get a better idea of what the gaps are that need to be addressed and where they might mandate electric replacements with little downside." Yes, exactly, and publish their findings perhaps in scenario or case study form so we can all have realistic information on what replacement might involve in our homes. Before your excellent blog posts, I would not have thought of space/clearance and electrical circuit issues in the context of a water heater.

@Mondoman: Fortunately, the industry has known about those limitations for a long time, which is why Rheem has the new Hydroboost model. It can use a standard plug -- no electrical work needed -- and it can go in any size room or closet as long as the inlet or outlet is ducted. (The latter is true for traditional models as well.) It's not quite as efficient as the traditional HPWH model since it heats water to a higher temperature. And it doesn't work in all climates. But it is a great option for our area imo.

Why do you assume CPAU Tier 2 rates of $0.20/kWh? Tier 1 rates are $0.144/kWh. Even when our children lived at home, we paid only Tier 1 rates.

Please speak up if you have information on a "combi" solution for Eichler homes that have both a standard gas water heater and a gas boiler to heat the water circulating through the radiant floors. Such a combined unit would be the last step needed to eliminate all natural gas appliances. And also another vote for induction cooktops - they rule!

Our gas waterheater is in a corner of the laundry room, not in a closet. Any problems with replacing it with a heatpump?

More great questions! My 2c: @Duveneck: Yeah, good question. It's partly because I want to err on the conservative side, and don't know how many people are in Tier 2. But it's also partly because as we electrify transportation and buildings, I expect that almost all of us will be in Tier 2 unless Palo Alto increases the size of Tier 1 (as PG&E has done) or provides a separate rate for EVs, or ... @Markie: Both Chiltrix and Harvest Thermal will heat both radiant (or fan coils) and hot water. Only Chiltrix will cool radiant as well. I get asked this question a lot. These combi systems are apparently pretty common in Europe. @Nan: The main downside I can think of is that in winter your heating bill would go up as the heat pump water heater works hard to cool that part of the house. It could also get uncomfortably cool for doing laundry. You might want to consider ducting the outlet to the outdoors if there is a convenient exterior wall and/or closing the door to the laundry room in the winter.

The local Rheem salesperson says that the dedicated and/or shared 15A Pro can only be purchased by a licensed contractor. The distributor is Pace. Pace says they expect to have hundreds in stock in late Sept or early Oct 2022. The list price for the 50-gallon model is about $4000. I have not had much luck finding a contractor that will do the installation. Got just have one quote so far at $12K which makes it a no go. I suspect a better quote would be for 8 hours of work at $150/hour for a labor of $1200 plus, say $3000 for a total of just over $4000. I have a rebate reserved from SVGE, plus the new IRA credit should make the installation a no-brainer. My gas bill to heat hot water runs about $60/month for two people in Los Gatos

@David, for installers, you might ask Pace who is in there a lot picking up HPWH's. Or look at Silicon Valley Clean Energy's list or Palo Alto's. Peninsula Clean Energy also has a list here, though it hasn't been updated in a while.

Very informative article, it allayed many of my concerns about HPWH; in particular, no one reports running out of hot water. However, there is a bit of confusion about units. You said " it generates 4200 BTU of energy ... equivalent to 1231 watts (at 3.41 BTU/watt)." But a BTU is a unit of ENERGY, and a watt is a unit of POWER (rate of energy use.) A Watt (1 Joule per second) is equivalent to 3.41 BTU PER HOUR. 4200 BTU PER HOUR would equate to 1231 Watts. I think one reason people get confused is because the Watt is a rate unit (1 Joule per second) but doesn't sound like it, and we use bastard units like "watt-hour" which is "joules per second hours", kind of like measuring distance in "miles per hour days". I'm taking a more serious look at HPWH now, mine would be powered by my surplus solar electricity. gotta figure out if my electric panel can handle it.

@Mark, thanks for reading so carefully and for pointing out the units problem. Apologies for the oversight, and it's been fixed!

Great column. And great timing. We are thinking about getting a HPWH this year. We just put more solar panels on the roof. Who would we reach out to first to see how feasible a HPWH is for our situation? We do have some interesting complications. * existing GWH is in an interior closet, not next to an exterior wall. ** it is plumbed for water, of course ** it is vented up for exhaust for the gas fumes ** the door has vents at the top and bottom. ** it has no electricity and no floor drain Don't know if any of these will prove to be showstoppers.

I think it's been mentioned, but I am jealous of your Palo Alto electric rates! Based on your numbers (thanks for the analysis!), a heat pump water heater would probably cost us nearly double in energy costs compared to our tankless gas heater. This makes me wonder if converting to a heat pump for winter house heating would also end up costing us more -- I'm guessing it would. :-(

@Proud, you might want to talk with and get estimates from a few installers. You can look at Silicon Valley Clean Energy's project list or Palo Alto's contractor list. Peninsula Clean Energy also has a project list, though it hasn't been updated in a while. I expect the question will not be whether it can be done but at what cost. @DrStrange: Not sure how you get to double the cost. If your tankless heater is a maximum 100% efficient, then the HPWH is "only" 3.7x more efficient, which translates to $2.38/therm if your electricity costs $0.30 (1 therm = 29.3 kWh). That is ballpark what PG&E charges for gas, definitely not 2x. Interesting question about a winter house or even a summer house. I agree that a house with frequent short stays, where the tank is cooling between visits, seems to be a better fit for a tankless heater.

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