My sister is in the process of building a house in Ohio, and I’ve been having conversations with her about how to make it green. She and my brother-in-law both consider me to be eco-crazed (arguably rightly so given the climactic and political stakes) and so tend to raise eyebrows when I make one of my many helpful suggestions.
For example, I suggested they install a central heat pump instead of inefficient electric resistance heating, but only after consulting their HVAC guy, who is a fan of heat pumps, did they decide to install one (Woo-hoo! They’ll save thousands of dollars and pounds of CO2 with that choice). They are also making their home solar-ready and plan to install panels in the next couple of years — this is mostly because solar offers a sense of self-reliance that is perennially popular across political and geographic boundaries.
However, when I tried to talk them into installing a heat pump water heater, I ran into serious resistance. If you haven’t heard about heat pump water heaters, they are an enormously powerful energy/CO2 reduction technology lying hidden in plain sight in the most humble of appliances — the water heater.
Water heating accounts for 25% of a home’s energy use, and thus offers an opportunity for big reductions in both pollution and cost. I’ve installed 3 heat pump water heaters (in my house, an accessory dwelling unit, and in a rental property), sung their praises for the last few years, and recently started a new job working on a national, non-profit led program called the Advanced Water Heating Initiative which seeks to make every new water heater use heat pump technology by 2030.
Heat pump water heaters move heat instead of creating it, using similar technology to a fridge or air conditioner, and are much more efficient than 20th century gas and electric resistant water heaters. Heat pump water heaters account for around 20% of new water heater sales in my state of Oregon and about 60% of sales in Maine, yet people haven’t heard of them in many places. This presents a barrier to adoption.
My sister and brother-in-law were, of course, interested in the fact that a heat pump water heater would save their family of 6 approximately $500 a year in electricity savings. But ultimately they cited their unfamiliarity with the technology and the fact that trusted contractors in their town hadn’t heard of them as a reason not to get one. In addition, they plan to put their hot water heater in a first floor hall closet and don’t want to vent it outside (in some conditioned spaces it’s best to vent a heat pump water heater outside). Finally, they used an interesting argument that inspired me to write this article, saying something to the effect of, “We’re installing solar panels next year so even if we go with the less efficient water heater it doesn’t really matter.”
This line of thinking got my wheels turning. How many solar panels would it take to power the extra electricity required for an electric resistance (aka typical, old electric) water heater compared to a heat pump water heater? And would it be more cost effective to get the extra solar panels or the more efficient water heater?
To answer these questions, I first looked up a 50-gallon heat pump water heater and compared it to an electric water heater by the same manufacturer (in this case Rheem). The heat pump water heater, according to Energy Star, uses 866 kWh (or $100) of electricity to make all the hot water a family would need for the year. The electric resistance water heater would use 3,493 kWh (or $400), which is 4 times the electricity and cost compared to the heat pump. These are average numbers, of course — the savings for my sister’s large family would likely be significantly higher. The difference between these two numbers is 2,627 kWh, which is about 25% of an average home’s electricity usage. Thus, using a heat pump water heater will reduce a typical home’s electricity usage by about a quarter. Note, I’m not even discussing gas because we’re trying to eliminate fossil fuels, and heat pump water heaters are 4-6x more efficient than gas ones anyway.
To make the 2,627 extra kWh that an electric resistance water heater will use, my sister will need an additional 2.2 kW of solar, which equates to about 7 more solar panels. With the average cost per watt of solar in the US at around $2.90, it would cost $6,380 to install this extra solar energy.
The average heat pump water heater, on the other hand, costs around $1,400 (though you can find them cheaper, especially with rebates) which is about $800 more than a typical electric water heater. Throw in a couple hundred bucks more for installation to vent the water heater (otherwise a heat pump water heater is comparable to installation costs of a standard electric water heater), and my back-of-the-envelope math shows that the extra 7 solar panels my sister will need will cost 6 times as much as a heat pump water heater ($6,000 for the panels versus $1,000 extra for the water heater).
To me this demonstrates the enormous potential of these unsung heat pump water heater heroes. They save as much energy as 7 solar panels for a literal fraction of the cost. This exercise could be useful for decision making about other clean energy technologies as well. Solar is still shiny, visible and exciting and we should all put panels on our roofs where possible, but if you’re investing for climate impact, it’s worth considering the CO2 bang for the buck.
Lesson learned here, next time you’re replacing your old electric or fossil gas water heater, consider a heat pump water heater, make your clean energy go further and help save 7 solar panels worth of clean electricity to power other parts of your hopefully soon to be all-electric abode.
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