Creating hot water is the second largest component of home energy consumption, accounting for 12% of a typical home’s energy use. In the United States, over 85% of residences use natural gas or standard electric water heaters, though they are not very efficient.
By pairing a new type of water heater with home solar power, you can expect much better energy savings and reduced operating costs.
In this article, we’ll review the shortcomings of existing residential water heaters, introduce you to how high efficiency heat pump hot water heaters work, and discuss how you can save big by pairing these systems with home battery backup systems with or without solar.
Shortcomings of different water heating types
Natural gas is a fossil fuel, emits carbon dioxide when burned, and sourcing it poses ecological problems. Gas water heaters are only about 50% efficient, as a lot of energy escapes through the vent. They are also a liability, especially in earthquakes as strapping is required to ensure they don’t rocket away from your wall and cause fires and more home damage.
Instant, tankless, or on-demand water heaters are only 30% more efficient than conventional gas or electric, and most of them still require natural gas to operate.
Solar thermal technology used to be the green option to heat water in your home a few decades ago. Solar thermal installations collect heat from the sun on your roof in a refrigerant, which then gets pumped into a one of two water tanks in your home. One is a pre-heat tank, which feeds the other.
In addition to requiring more space, solar thermal systems can cause problems on roofs over time with their added weight and propensity for leakage. Moreover, you also have to wrap each tank tightly with blankets to ensure heat doesn’t escape as quickly. Solar thermal water heating used to be the most green option to heat water until heat pump hot water heaters arrived.
The main problem with traditional electric hot water heaters is they use a lot of electricity.
“I calculated that over a year, my old electric hot water heater will use about the same amount of energy my electric car would need to cross the country 4 times”, says Joe Wachunas director of solar advocacy group Solar Oregon. “Heat pump hot water heaters are much better and what I consider the 21st century water heating technology”.
How heat pump hot water heaters work
To understand how heat pumps work, first consider the word, ‘pump’. If you’re using an air pump, you’re moving air from one place to another, say to your bicycle tire. With a heat pump, you’re moving heat from one place to another.
Heat pumps are not new to us, and we all have them in our refrigerators at home. Heat pumps in our refrigerators remove heat from the enclosed area and expel it into the outside. That’s why the backside coils are usually quite warm.
Heat pump hot water heaters are much more energy efficient because it’s a lot easier to move heat than create heat. They use electricity to move heat from the surrounding air and transfer it to water in a storage tank. It’s like a refrigerator in reverse!
Their performance relies on the level of heat in your air, so there are slight fluctuations in efficiency based on seasonality and where and how they are vented.
When you need more heat for your water than is available by moving heat from the air into your unit, the electric rods activate in the tank, functioning like a conventional electric water heater. That’s why heat pump hot water heaters are also called hybrid electric water heaters.
Effective setups draw warm air from your attic down into the unit, which then expels the cooler air back into your home or outside, based on the season. In this way, you can simultaneously heat your water and cool your air. Talk about a powerful setup.
Heat pump hot water heaters can even be configured to supply hot water to radiant flooring setups in the image above.
Benefits of Heat Pump Water Heaters
Again, because heat pump hot water heaters primarily move heat rather than create it, they are much more energy efficient than other tank types.
Heat pump water heaters are three times more efficient than electric, and four times more efficient than gas.
Cost competitive savings
The Rheem model above retails for about $1000, has a 10-15 year lifespan, and qualifies for a $300 Energy Star federal tax credit. Some electric companies also offer upfront rebates and incentives for heat pump hot water heaters, which when combined with the tax credit can pay for themselves in just 2 to 3 years.
Really cheap to run
As you can see from the Energy Guide tag on the product, the fiscal performance of heat pump hot water heaters are literally off the charts. The Energy Trust of Oregon estimates a heat pump hot water heater can save up to $90 per person in your household annually.
Extra energy storage option for when your batteries are full
Since heat pump hot water heaters use electricity, they pair extremely well with home battery backup systems and solar panels. They can act as thermal batteries, storing heat in water heated with clean electricity from your rooftop solar installation during the day for use later in the evening.
Many models integrate well with smart home apps, so you can program when to be heating your water and put your system in standby or vacation mode with the tap of a few buttons on your phone.
If you live in an area with a time of use rate structure or in an area with a limited net metering program, you can save extra money by turning your heat pump hot water heater into an additional battery. Similar to how you charge up your phone to be used for the rest of the day, heat pump hot water heaters can heat water hours in advance and provide very relaxing hot showers during the evening hours, when your electricity costs may be higher.
Doing so can shift electricity demand away from peak times to when costs are lower and more solar energy is abundant on the grid. We’d like to see more utilities offer incentive programs to help people couple this technology with batteries and solar. It’s a win-win for everyone.
Last modified: April 10, 2020