Heat Pump Water Heaters — Game Changers In Efficiency

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By Joe Wachunas, Solar Oregon

On the journey to making our homes money savers and climate champions, water heating has always been a stumbling block. While there are easy ways to use hot water efficiently (like the low-flow shower heads we featured in this Go Zero Hack), it’s a challenge to heat water without polluting.

The issue is that, until recently, heating anything almost always meant burning something. And burning things creates pollution. Let’s call this dilemma, “the heating conundrum.”

All types of heating, including water heating, face this conundrum. For example, most people today still use the early-generation, archaic technologies of our parents and grandparents. They either use:

  • Electric water heaters (40% of the US Northwest (NW) market), which use a lot of electricity, enough per year to allow my electric car to drive about 16,000 miles. In the past, much of that electricity was produced by burning fossil fuels, but that is changing with electricity getting cleaner really quickly. Yet, typical electric water heaters remain very inefficient.
  • Gas hot water heaters (33% of the NW market), in which gas is pulled from the ground (often in ways that pollute) and shipped to your house and burned. Only 50–60% of the energy that is used to heat the water actually does — the rest is wasted through venting.

About 15 years ago, as climate change started to breathe down our necks, some smart people started developing alternative water heating technologies to address the heating conundrum. They created:

  • Instant water heaters (13% of the NW market), which heat water on demand, only when you turn on the faucet or shower. This makes instant hot water heaters extra efficient because you don’t keep a 50 gallon tank of water piping hot for the 23 hours a day you’re not using it. But most instant hot water heaters still use gas, which means burning and polluting (just more efficiently).
  • Solar water heaters (<1% of the NW market), which use the sun to heat your water. You put a solar collector on your roof and the sun heats fluids which then heat the water. The problem with these systems is that they are expensive, and some have required significant repairs and need a backup source of water heating in the winter (either gas or electric.)

So in summary, until recently, we’ve been stuck burning things in inefficient ways to heat our water.

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A Way out of the Conundrum

And then, in the last 5–10 years, a new kid on the block appeared — heat pump water heaters. Heat pump water heaters (HPWH) hold tons of promise for getting us out of the heating conundrum and becoming the water heating method of the 21st century.

New Kid on the Block — Heat Pump Water Heater. Image Courtesy Rheem.

They’re crazy efficient. Heat pump water heaters are 7 times more energy efficient than gas and 3.5 times more efficient than electric water heaters.

How is that possible? Magic. Well, not really magic, but what seems like magic. It’s the same magic that makes your fridge or air conditioner work — heat pump technology.

Heat pumps move heat from one place to another. They are so efficient because they don’t make heat, but rather they move it from one place to another. Like magic.

Little diagram on how heat pumps water heaters work from energystar.gov
Emissions from electricity have fallen off a cliff — just what we need them to do.

HPWHs use electricity — Not only are they crazy efficient, but heat pump water heaters use electricity, which gives us a recipe for clean water heating. Electricity is getting dramatically cleaner all the time. We’re burning fewer and fewer things and capturing more electricity from sunlight and wind. Renewables in the U.S. have doubled in the last 10 years and coal use has been cut in half.

Heat pump water heaters don’t cost that much to buy or operate — Unlike solar hot water heating, heat pumps don’t cost an arm and a leg. They cost a little more than gas or electric hot water heaters and there are often rebates that bring them to price parity. And because they use electricity so efficiently, they cost very little to run. We’re talking $100 year for an average family’s needs.

Average cost of running a heat pump water heater.

My Family’s Story

Since we bought our home in 2012, my family has been on a path to use cleaner sources of energy for our home. We want to both save money and get as close to zero carbon emissions as possible.

Changing all your home’s systems at once can be intimidating, so we’ve done things in stages and saved one clean energy/energy efficient investment per year. For example, in 2012, we bought one set of solar panels. In 2013, we replaced our gas furnace with ductless heat pumps. In 2016, we got another set of solar panels to meet our increased electric demand. In 2017, we bought a used Nissan Leaf (our first car, for just $7,500). In 2018, we bought heat pump hot water heaters.

Our weird little triplex of a house.

The plural is accurate because we replaced two water heaters — one in our main house, a 20 year old gas beast, and another in our accessory dwelling unit, which also provided hot water to the radiant floor system.

The water heater in our garage apartment was a lesson in stranded assets, something we invested in but did not get the full life out of because we bought the gas unit in 2012 and replaced it with heat pump technology just 6 years later. The world will likely have a lot of stranded assets as we transition to fully clean energy systems. In our case, as we gradually moved towards a clean energy home, the gas hot water no longer made sense even though it wasn’t yet at the end of its life.

My research into heat pump hot water heaters two years ago left me with a lot of questions given they were still pretty new in the market. Some recommendations insisted they had to be placed in a garage or basement because they made noise and exhausted cool air, effectively cooling the surrounding space. Both our existing water heaters were located in utility closets in primary living spaces and we didn’t have a garage or basement to house the a HPWH.

Long story short, after a lot of research and a bit of risk, we found that they aren’t noisy and do not cool the space significantly if they are properly ducted (ours exhaust to the attic).

My HPWH pulls heat from the attic and exhausts cold air. Don’t judge the ugly ducts.

The success we’ve found with these water heaters has followed a predictable and pleasantly surprising pattern for us. In our experience, when we’ve gone out on a limb and experimented with a new technology, or lifestyle choice, for the sake of cleaner energy and our world, it has always paid off in spades.

And our hot water heaters have paid off in spades. Over the course of a year, we replaced both gas water heaters, one old and one new(ish), with heat pump hot water heaters. We ducted both into the attic, and on summer days, they pull heat from the hottest place in our home and use it to heat our water (they do this on winter days too — like I said before, magic!). And they work like a dream. The HPWH in our house provides hot water for 3 showers and 6 people (our family of 4 plus our Airbnb unit), and the one in the apartment heats water for one shower but also runs the radiant floor heating system which provides all space heating for the unit.

In my garage apartment, the heat pump water heater also runs the radiant floor heating system.

And when the sun is shining, and our solar panels are collecting photons to make electricity, it’s particularly satisfying to take a shower or run the dishwasher, knowing all the energy to heat the water comes from the sun.

Heat pump water heaters have allowed my family to find our way out of the heating conundrum. We can have our cake and eat it too — all the hot water we need without polluting the earth, and saving money by heating water incredibly efficiently. These HPWHs have ushered in an era of clean, 21st century showers and baths and dishwashing for my family. Join us — the water is fine.

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