Why Did My Water Heater Energy Use Rise?
As I’m sure you do, I track my energy use at home. I’ve got a spreadsheet with the data from all of my electricity bills since we moved into this house in 2019. I also track individual parts of my home energy use. And that’s how I know I had a huge rise in my heat pump water heater energy use in 2024 and 2025. We’re back to normal this year—and may even end up with our lowest annual energy use so far—but what caused that rise?
The graph below shows the annual energy use of my heat pump water heater. The 2026 column, though, includes an estimate for the last four months of the year. We had a slow rise going on from 2020 to 2023. Then in 2024, our energy use was 89 percent higher than it was in 2020. And 2025 was also abnormally high. What happened?
A likely suspect
If you’ve been reading this blog for two years or more, you may remember a big project I undertook in 2024. Beginning in February of that year, I gutted and remodeled my basement. The air was filled with dirt and dust and particulates and probably other airborne filth, too. And I didn’t always remember to cover and turn off the water heater.
For a regular electric or gas water heater, that doesn’t matter so much. But a heat pump water heater gets its heat from the indoor air. When the air is dirty, the filter gets dirty. And as I discovered, the coil and other components can get dirty, too. Here’s a photo of the filter in January of 2025.
And here’s what it’s supposed to look like.
So, were the dirty filter and heat pump coil responsible for the high energy use of the water heater in 2024 and 2025? It seems likely, doesn’t it?
Monthly energy use data
Before jumping to conclusions, though, we need a more granular look at the data. The graph below shows the monthly data for our heat pump water heater.
From 2020 through mid-2023, the energy use was pretty regular. It was high in the winter, at about 60 kilowatt-hours (kWh) per month, and low in summer, at 20 to 30 kWh per month.
When I graphed these data recently, the huge drop in the middle of July 2025 stood out to me. That wasn’t long after I cleaned the coil in the heat pump water heater (video below). That had to be it. Right?
But already I see a problem with blaming the renovation for the extra energy use. Notice the steep rise at the end of 2023. The renovation didn’t begin until February of 2024. Hmmm.
The primary reason
OK, I need to say more about what was going on in our house starting in August of 2023. My stepson, who prefers baths to showers, moved in with us then and stayed for two years. Then he moved out at the end of July 2025. Also, I cleaned the coil in the water heater in April 2025 three months before the big drop in July. The graph below is the same one I showed above but with annotations.
The jump in energy use began when my stepson moved in and then went back to normal after he moved out. I’m sure the dirty filter and coil had an impact on the energy use. I really wanted that to be the primary cause. But the jolt in energy use those two years actually was caused by both things. I can’t fully disentangle the two without knowing the monthly hot water use as well as the energy data.
Also, there’s another contributing factor I haven’t mentioned yet. Yes, the renovation made things worse by getting the filter and coil dirty. But it also made things better by putting the heat pump water heater into fully conditioned space. Before the winter of 2024-25, we didn’t have heat in the basement. So, the higher ambient air temperature near the water heater made it more efficient. Without that, the peaks from November through January that winter would have been higher.
The extra energy use from the dirty filter and coil had to be significant, especially when the filter was clogged with drywall dust as you see in the photo above. So, if you have a heat pump water heater, here are some ways to keep it operating efficiently.
- Turn off and cover the water heater during dust-making events like remodeling.
- Upgrade the filtration.
- Check the filter regularly, and clean it when necessary.
- Clean the heat pump coil and other components when they get dirty.
Oh, and monitor your energy use. It can tell you a lot.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel.
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My heat pump water heater elec usage went way way down after I had to have my Dallas slab home re-piped from the slab copper plumbing to an all PEX attic home run system. I’m getting the benefit of the very hot summer in Texas, but will likely pay some back in the winter.
Bruce: Yeah, uninsulated copper embedded in a concrete slab is a great way to boost your hot water energy use.
I thought that was called radiant floor heating 😉
True! Good one, Roy.
And no children allowed in the house!😉
Ed: Well, that’s not always realistic…unless we move to a retirement home that doesn’t allow them. :~)
Really liked the idea of heat pump WH and tried one (Lexington, KY) a few years ago. Lasted a week. Turns out, according to the technician, that the wiring harness was located immediately above the tank, causing an inevitable issue. So, went back to traditional electric element type. Then I got to thinking……Having located it in our conditioned basement, during the heating season, ultimately heat will be provided by the central house system. Best place to locate these is in a more temperate climate, south of Kentucky where the water heater is independent of the house system. Thoughts?
Bruce: When placed indoors, a heat pump water heater does indeed use heat from your space heating system to heat water. So if you’re burning coal to heat your home—as some people do in Kentucky—it’s not a great idea. But if you’re using an efficient heating system, it’s fine. This is on my list to write about.
But there’s also another type of heat pump water heater that doesn’t use heat from indoors. It’s the split-system HPWH.
The split system sounds very promising. And given the advances in inverter compressor technology, gotta be much more efficient than the toaster technology I’m currently using.
Actually, the split (actually combo) system that I want uses a single heat pump both for refrigeration and hot water. If the household uses lots of hot water perhaps put that split outside unit inside a home-style walk in cooler.
I installed a tankless gas water heater when my tank-type one failed. With individual hot and cold taps on my shower (and sinks) I learned that I can shower using only the full-on hot tap at 104 degrees without mixing in any cold water at all. I get wet, turn off the single hot tap and then turn the hot tap back on when ready to rinse off. This significantly cuts down on my water use and avoids the shock of trying to find the sweet spot of mixing in cold and 120+ degree hot water.
William: That sounds like a good adaptation for your situation. But that seems like a lot of heat lost by the water on its way from the water heater to the showerhead.
Over the past 20 years we’ve found that one of the most cost effective energy saving changes in a house can be installing a lower volume shower head. Not sure if there are lower volume flow restriction devices for the tub spigot but if not perhaps there’s a business opportunity to be had!
Wouldn’t the energy use due to a bath depend on how far you fill the tub rather than how fast the water entered it?
Roy: It also depends on how long you stay in the tub and keep the hot water running.
Brian: Yes, low-flow showerheads are great. The US Energy Policy Act of 1992 mandated low-flow fixtures for plumbing systems, with showerheads required to be no higher than 2.5 gallons per minute (gpm). The ones in my house are 1.5 gpm, and they work great. The one I use is the High Sierra Classic. Here’s the Amazon page for it:
https://amzn.to/46yJRJv (affiliate link)
Trying to restrict the flow at the tub faucet doesn’t make a lot of sense because people don’t want to wait ten minutes to be able to bathe.
I was only kidding about the restriction on the tub faucet! We’re huge fans of the Evolve 1.25 GPM showerhead unit with the ShowerStart feature the slows the flow to a trickle once the water reaches 95 degrees then resumes full flow upon pulling the cord! Kinda fail-safe, if you will, for the forgetful or soon to be forgetful types!
https://www.lowes.com/pd/Evolve-ShowerStart-1-Spray-Pattern-with-1-25-GPM-3-25-in-Massage-Fixed-Shower-Head-with-Hot-Water-Saving-TSV-Valve-in-Chrome/5015549643?user=shopping&feed=yes&srsltid=AfmBOoozbgZv-RSJ7LwmSBajOphsIfM34pNaq7XphEdRRubjkr75pbXdwpE
A water meter on supply to the HP water
heater may be a useful data set going forward.
Thank you for the articles .
Bob
Bob: Yes, I bought a water meter for that purpose a few years ago. It’s one of my many unstarted or incomplete projects. [Sigh.] Some day!
While we are on the topic of domestic water heaters, has anyone tried heat recovery where the supply water line to the water heater recovers heat from the shower drain via a heat exchanger? I have seen several products on the market but have never seen one in use. It looks like a pretty simple concept especially if your shower is above a basement and near the water heater.
Roy: I don’t have one, but they’re somewhat popular in the Toronto area. I’ve seen several there.
My heat pump water heater is in a closet in the hot Dallas garage. I ducted the intake and cold output air to the garage area where it takes a few degrees off. It doesn’t run enough to do a lot of cooling however.
Allison –
By chance are you on municipal water? Reason I ask is that your home’s water use certainly increased while your stepson was aboard, and the periodic water bills would quantify that increase. At back-of-envelope precision you could assume the portion of hot water use to overall water use stayed the same, allowing you to guesstimate the additional hot water attributable to your stepson.
The bath vs shower difference is really hard to quantify – we have had teens who managed to daily singlehandedly empty an 80 gallon nominal / 72 gallon actual water heater…fortunately a Rheem HPWH similar to yours!
Curtis: Yes, we’re on municipal water, but I don’t think that would help a lot. There were periods of high water use during the remodeling that would be difficult to disaggregate from the increase in hot water use.
Cleaning my refrigerator coils, The coils are hard to reach and still dirty after brush / vacuuming them.
I used an air compressor with a extended tip nozzle. Much better results.
I imagine it’s hard to reach the coil in a HPWH. But, results will be better than a filter clean alone.