Happy Heat Pump Water Heater Day!

October 25, 2023, is Heat Pump Water Heater Day! So that makes today the perfect time to talk about one of the most important appliances, the noble heat pump water heater. Heat pump water heaters, or HPWHs to their friends, are an essential tool in decarbonizing buildings and thus in helping to address the climate crisis.

Background

Buildings are an enormous source of carbon emissions in the United States, directly and indirectly accounting for about 30 percent of the nation’s total emissions. (This allocates the electricity sector’s share of emissions to end-use sectors proportionate to the amount of electricity consumed by those sectors; as my former colleague and I have explained, this is necessary to appreciate the full extent of the issue.) According to the EPA’s Greenhouse Gas Inventory, in 2021 the U.S. emitted 6,340.2 million metric tons of CO₂ equivalent that year. That makes the building sector’s share of emissions over 1,900 million metric tons.

When it comes to residential buildings, water heating accounts for just over 18 percent of all U.S. household energy consumption according to data from the federal Residential Energy Consumption Survey. A “good” gas water heater will have an efficiency in the 90-ish percent range. An electric resistance water heater is essentially 100% efficient. That marginal improvement is a pale comparison to to HPWHs, however. They move heat from surrounding air and places it in the water rather than directly creating heat. That makes it much more efficient, in some cases exceeding 300 percent efficiency.

That magical-seeming efficiency is what makes them such a powerful decarbonization tool. Replacing old-fashioned, inefficient water heaters with heat pumps slashes energy consumption. That in turn drives emissions down; according to the New Buildings Institute switching to a HPWH saves more than 2,000 pounds of CO₂ annually.  It also drives utility bills down – according to ENERGY STAR a family of four would save $550 a year using a HPWH!

How can we get more HPWHs into people’s homes?

There are two landmark policies that will help with this. First, as my colleague Lauren Urbanek has written, the Inflation Reduction Act is a powerful tool to help homeowners access efficient products, HPWHs included.

Second, last month the Department of Energy finished collecting comments on a proposal that, when finalized, would help drive the market toward the magical heat pump water heater.

As part of its efficiency standards program—one of the most impactful emissions-reducing programs the federal government has in its toolkit—DOE has proposed critical increases to the minimum energy efficiency of new water heaters. (DOE’s proposal was very similar to a recommendation negotiated by a coalition of stakeholders, including NRDC.) What that means is, after the rule is finalized and fully in effect, new water heaters will have to be much more efficient. In particular, the vast majority of new electric water heaters (with some exceptions for specific applications, particularly space-constrained installations) will have to use heat pump technology.

For consumers, this doesn’t mean any changes to your existing water heater, and the regulation does not require early retirement of existing products. But once the regulation is in effect, your next water heater will be much more efficient, and more affordable too. By shifting most of the electric water heater market to heat pumps and thus increasing their market share, the cost of heat pumps will decrease through economies of scale. The standards will particularly benefit renters, whose landlords often buy cheap, inefficient products, sticking renters with the higher utility bills.

Conclusion

There is no single silver bullet that will deliver us to a climate-safe future, nor is there one to solve the building sector’s share of emissions. Fortunately, however, heat pumps are a versatile tool that can get us a lot of the way there. But they won’t just magically appear in people’s homes, we need policies to increase their availability and affordability. Policies like the Inflation Reduction Act, and DOE’s efficiency standards, are just the thing. It might not be as fun as a birthday or Halloween, but the incredible potential of this climate-friendly appliance makes Heat Pump Water Heater Day a holiday worth celebrating in my book.