What Caused My Water Heater's Energy Use to Jump?

A two-year surge in electricity use suggested a dirty filter and coil, but a closer inspection pointed to another factor as well

I keep close tabs on my home energy use, including a spreadsheet of every electricity bill since we moved into this house in 2019. I also track individual pieces of the home’s energy load. That is how I noticed a major increase in the energy use of my heat-pump water heater in 2024 and 2025. This year, things are back to normal—and may even end up as our lowest annual use yet—but what caused the spike?

The chart below shows the yearly energy use of my heat-pump water heater. The 2026 column includes an estimate for the final four months of the year. Usage crept up from 2020 through 2023, then in 2024 it was 89% higher than in 2020. It remained unusually high in 2025. So what changed?

A likely culprit

If you have followed this blog for a couple of years, you may remember a major project I took on in 2024. Starting in February of that year, I gutted and remodeled my basement. The air was full of dust, dirt, particulates, and probably other airborne grime. And I did not always remember to cover and shut off the water heater.

That may not matter much for a standard electric or gas water heater. But a heat-pump water heater draws heat from indoor air. When the air is dirty, the filter gets dirty too. As I found out, the coil and other parts can get dirty as well. Here is a photo of the filter in January 2025.

And here is what it is supposed to look like.

So were the dirty filter and heat-pump coil the reason for the water heater’s high energy use in 2024 and 2025? That seems plausible.

Monthly energy use data

Before settling on that explanation, though, the data need a closer look. The chart below shows the monthly energy use for the heat-pump water heater.

From 2020 through mid-2023, the pattern was fairly steady. Energy use was highest in winter, around 60 kilowatt-hours (kWh) per month, and lowest in summer, at roughly 20 to 30 kWh per month.

When I recently graphed the data, one sharp drop in the middle of July 2025 stood out. That was not long after I cleaned the coil in the heat-pump water heater (video below). So that must have been the explanation, right?

But there is already a problem with blaming the renovation alone for the extra energy use. Notice the steep increase at the end of 2023. The remodel did not begin until February 2024.

The main reason

I should add what was happening in our house starting in August 2023. My stepson, who prefers baths to showers, moved in then and stayed for two years before moving out at the end of July 2025. I also cleaned the water heater coil in April 2025, three months before the big drop in July. The chart below is the same one above, now with annotations.

The rise in energy use started when my stepson moved in and then returned to normal after he moved out. I am sure the dirty filter and coil affected energy consumption, and I wanted that to be the main explanation. But the increase over those two years was really caused by both factors. Without monthly hot water-use data, I cannot fully separate the effects.

There was another factor too. The renovation made matters worse by loading the filter and coil with dust, but it also improved performance by placing the heat-pump water heater in fully conditioned space. Before the winter of 2024-25, the basement was unheated. The warmer air around the unit made it more efficient. Without that benefit, the winter peaks from November through January would have been higher.

The extra energy use from the dirty filter and coil must have been substantial, especially when the filter was clogged with drywall dust like the one shown above. If you have a heat-pump water heater, here are some ways to keep it running efficiently:

1. Turn off and cover the water heater during dust-producing work such as remodeling.
2. Improve the filtration.
3. Inspect the filter regularly and clean it when needed.
4. Clean the heat-pump coil and other components when they become dirty.

And keep an eye on your energy use. It can tell you a lot.