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Heat-pump water heaters What to know?

Most homeowners who have heat pumps use them to heat and cool their homes. But a heat pump also can be used to heat water -- either as stand-alone water heating system, or as combination water heating and space conditioning system.

How a heat-pump water heater works

Heat pump water heaters use electricity to move heat from one place to another instead of generating heat directly. Therefore, they can be two to three times more energy efficient than conventional electric resistance water heaters. To move the heat, heat pumps work like a refrigerator in reverse.

While a refrigerator pulls heat from inside a box and dumps it into the surrounding room, a stand-alone air-source heat pump water heater pulls heat from the surrounding air and dumps it -- at a higher temperature -- into a tank to heat water. You can purchase a stand-alone heat pump water heating system as an integrated unit with a built-in water storage tank and back-up resistance heating elements. You can also retrofit a heat pump to work with an existing conventional storage water heater.

Heat pump water heaters require installation in locations that remain in the 40º–90ºF (4.4º–32.2ºC) range year-round and provide at least 1,000 cubic feet (28.3 cubic meters) of air space around the water heater. Cool exhaust air can be exhausted to the room or outdoors. Install them in a space with excess heat, such as a furnace room. Heat pump water heaters will not operate efficiently in a cold space. They tend to cool the spaces they are in.

You can also install an air-source heat pump system that combines heating, cooling, and water heating. These combination systems pull their heat indoors from the outdoor air in the winter and from the indoor air in the summer. Because they remove heat from the air, any type of air-source heat pump system works more efficiently in a warm climate.

Homeowners primarily install geothermal heat pumps -- which draw heat from the ground during the winter and from the indoor air during the summer -- for heating and cooling their homes. For water heating, you can add a desuperheater to a geothermal heat pump system. A desuperheater is a small, auxiliary heat exchanger that uses superheated gases from the heat pump's compressor to heat water. This hot water then circulates through a pipe to the home's storage water heater tank.

Desuperheaters are also available for tankless or demand-type water heaters. In the summer, the desuperheater uses the excess heat that would otherwise be expelled to the ground. Therefore, when the geothermal heat pump runs frequently during the summer, it can heat all of your water.

During the fall, winter, and spring -- when the desuperheater isn't producing as much excess heat -- you'll need to rely more on your storage or demand water heater to heat the water. Some manufacturers also offer triple-function geothermal heat pump systems, which provide heating, cooling, and hot water. They use a separate heat exchanger to meet all of a household's hot water needs.

Selecting a Heat Pump Water Heater

Heat pump water heater systems typically have higher initial costs than conventional storage water heaters. However, they have lower operating costs, which can offset their higher purchase and installation prices.

Before buying a heat pump water heating system, you also need to consider the following:

Size and first hour rating
Fuel type and availability
Energy efficiency (energy factor)
Overall costs

If you're considering installing an integrated water heating, space heating, and cooling heat pump system in your home, also see our information about air-source heat pumps and geothermal heat pumps.

Installation and Maintenance

Proper installation and maintenance of your heat pump water heating system can optimize its energy efficiency.

Proper installation depends on many factors. These factors include fuel type, climate, local building code requirements, and safety issues. Therefore, it's best to have a qualified plumbing and heating contractor (or geothermal heat pump system installer/designer) install your heat pump.

Do the following when selecting a qualified professional:

Request cost estimates in writing
Ask for references
Check the company with your local Better Business Bureau
See if the company will obtain a local permit if necessary and understands local building codes.

Periodic water heater maintenance can significantly extend your water heater's life and minimize loss of efficiency. Read your owner's manual for specific maintenance recommendations.

Improving Energy Efficiency

After your water heater is properly installed and maintained, try some additional energy-saving strategies to help lower your water heating bills. Some energy-saving devices and systems are more cost-effective to install with the water heater.

How Your Water Heater Can Be a Secret Weapon in the Climate Change Fight

California wants to replace millions of gas water heaters with high-tech electric ones to serve as “thermal batteries” for storing solar and wind energy.

Todd Woody

February 11, 2021, 4:00 AM MST

Nearly every home has a water heater, but people tend not to think about it until the shock of a cold shower signals its failure. To regulators, though, the ubiquitous household appliance is increasingly top of mind for the role it could play in reducing greenhouse gas emissions and weaning the power grid from fossil fuels

High-tech electric water heaters can double as thermal batteries, storing excess production from wind and solar generators. In California, officials aim to install them in place of millions of gas water heaters throughout the state.
That would reduce the need to fire up polluting fossil fuel power plants to supply electricity for water heating after the sun sets.

“Water heaters have significant potential,” says Commissioner Clifford Rechtschaffen of the California Public Utilities Commission. “We know we’ll need a tremendous amount of storage to get to our decarbonization goals. We’re challenged now in evenings when renewable energy production declines and demand peaks.”

The focus is on heat pump water heaters, which transfer warmth from the atmosphere to a tank. They’re up to four times as efficient as conventional gas or electric water heaters. Nationwide, about half of water heaters are powered by natural gas. In California, water heating is one of the biggest consumers of fossil fuels and gas water heaters account for 90% of the market. Swapping them for heat pump versions could reduce greenhouse gas emissions from water heating in the state by as much as 77%, according to a paper published in January by the nonprofit New Buildings Institute.

Here’s how using heat pump water heaters for energy storage works:

When renewable energy production peaks in the afternoon, a signal is sent that activates heat pump water heaters. After heating water, the devices shut down and store the hot water for use in the evening when demand spikes. That puts to use excess renewable energy generated during the day that would otherwise be wasted. Grid operators could also charge these thermal batteries as needed to balance supply and demand or before a planned power outage due to wildfire threats or in anticipation of extreme weather that could trigger blackouts. It’s estimated that heat pump water heaters could store hot water for 12 hours or more, depending on the size of the tank.

Water heaters typically have lifespans of 12 to 15 years and about 800,000 of them fail annually in California, according to Pierre Delforge, a senior scientist at environmental group Natural Resources Defense Council in San Francisco. He says replacing them with programmable, WiFi-enabled heat pump devices would create a network of thermal batteries that could be charged with renewable energy as needed.

“We’ll have millions of batteries that are useful to the grid and that will make it cleaner,” Delforge says.

A 2018 paper he co-authored for the nonprofit American Council for an Energy-Efficient Economy modeled the potential impact of using heat pump water heaters for energy storage. The study found such a network would lower utility bills, boost renewable energy consumption, and strengthen the reliability of the power grid.

Climate-Proofing Your Home: Improving Your Backup Power Supply

California regulators have recognized the potential of heat pump water heaters—which currently comprise just 1% of the state's heating market—to meet the state’s aggressive climate targets. In 2020, they approved an initial annual budget of $44.7 million to promote the adoption of heat pump water heaters.

That’s a small down payment on a goal that could cost hundreds of millions of dollars to achieve over the next decade. Regulators are currently developing a statewide incentive program set to launch later in 2021. Rechtschaffen says the CPUC is still evaluating the mix of incentives, but they will likely include rebates to encourage homeowners and contractors to adopt heat pump water heaters. That would spur market demand, resulting in lower manufacturing and installation costs so that heat pumps would become competitive with gas water heaters.

Meanwhile, three California utilities are running pilot projects that offer rebates to customers who install grid-connected heat pump water heaters so their performance as thermal batteries can be evaluated. Another two utility programs are awaiting regulatory approval. The state’s two largest utilities, Pacific Gas & Electric Co. and Southern California Edison Co., are planning multimillion-dollar pilot projects to create networks of 6,400 and 17,000 heat pump water heaters, respectively.

Heat pump water heaters are about twice as expensive as conventional water heaters and installation costs can add thousands of dollars. The majority of California’s nearly 14 million homes were built before 1980 and many would need an upgrade to the electrical panel to handle the extra load from a heat pump water heater. Such upgrades can run between $3,000 and $6,000.

“It’s definitely a huge hurdle,” says Rachel Kuykendall, senior program manager at Sonoma Clean Power, a Northern California utility. Last April, Sonoma Clean Power added heat pump water heaters to its GridSavvy program, which gives customers a $5 credit on their monthly bill if they allow the utility to control household devices such as smart thermostats and electric vehicle chargers to maximize the use of renewable energy and balance the grid.

Climate-Proofing Your Home: How to Electrify

The modest $5 incentive aside, Sonoma Clean Power customers can qualify for rebates of up to $2,000 to purchase a heat pump water heater. Later this year, the utility will roll out a 0% interest loan program that can be tapped to finance electrical panel upgrades. So far, 100 water heaters are among the 969 devices currently controlled by GridSavvy.

“I honestly think heat pump water heaters are probably one of the best resources out there for decarbonization,” says Kuykendall, noting that when a heat wave hit Northern California last August, GridSavvy helped the utility to avoid a blackout. “We were able to use this to keep the lights on.”

Inefficient conventional electric water heaters—which use an electric heating element—are common in other regions of the U.S. That means those homes already have electrical panels capable of powering heat pumps, making a switch cheaper and quicker, according to Amruta Khanolkar, a project manager at the New Buildings Institute in Portland, Oregon.

She says that later this year three big makers of heat pump water heaters, General Electric Co., Rheem Manufacturing Co., and A.O. Smith Corp., are expected to introduce versions that can be plugged into standard 120-volt panels, eliminating the need for expensive electrical upgrades. (The trade-off is that such water heaters may not be suitable for colder climates.)

“We’re currently in a climate emergency and in a pandemic where people are working from home and using more energy for water heating,” says Khanolkar, who manages the Advanced Water Heating Initiative, a coalition of manufacturers, utilities, and government agencies. “The residential sector is now even more critical for decarbonization.”

California Is Closing the Door to Gas in New Homes

The state aims to reduce natural gas use for home heating and hot water as part of its bid to lower emissions

By Anne C. Mulkern, E&E News on January 4, 2021

California's top energy bosses soon will decide when to snuff out natural gas flames in new homes.

The seismic move toward omitting some gas appliances comes as the California Energy Commission retools state building codes for energy-efficient homes. It's an expansion of the state's first-in-the-nation mandates requiring solar panels on all new homes starting last year.

The agency now plans to tighten rules on natural gas for home heating and hot water, a code update that would take effect in 2023.

Environmental groups want a complete ban on natural gas in new homes, but the state commission has signaled that isn't likely right now. Officials instead in the coming months are likely to use incentives to urge developers to pick electric options for heating, like heat pumps. More muscular requirements could come later.

"We are really ratcheting up the efficiency across the board," agency Commissioner Andrew McAllister said in an interview. "We anticipate that we'll be providing incentives for the market to scale up its adoption of heat pumps."

"You need to give the marketplace reasons to adopt it before you step in and maybe mandate it," McAllister added. "That's the pathway that we're likely on."

The long-term outlook for natural gas isn't good in California, which wants to eliminate most carbon emissions by 2045. Gov. Gavin Newsom (D) injected urgency into state climate efforts this summer after wildfires scorched more than 4 million acres, a new record.

The California Building Industry Association, a trade group whose members develop 85% of new buildings in the state, is girding for ever-tougher rules over the next five years.

"The writing's on the wall," said Bob Raymer, technical director with the industry group. "They're going to want electric space and water heating come 2026."

The use of natural gas in buildings creates about 10% of California's greenhouse gas emissions, according to the California Air Resources Board.

That agency in November urged "stronger kitchen ventilation standards and electrification of appliances, including stoves, ovens, furnaces, and space and water heaters, in the 2022 code cycle for all new buildings."

Those moves would set new benchmarks nationally and are intended "to protect public health, improve indoor and outdoor air quality, reduce GHG emissions, and set California on track to achieve carbon neutrality," said CARB.

They come as more than 40 cities and counties in California have tightened rules on natural gas use in new homes. A few have banned it entirely, including San Francisco. Environmental groups are pushing to eliminate gas from new residential construction immediately, a move that they say would prevent new homes from releasing emissions for decades to come.

"We don't have another three years to wait on this," said Matt Vespa, an attorney at Earthjustice. "There's a lot of momentum here."

Even San Francisco-based utility Pacific Gas and Electric Co., which has 5 million customers, said that it supports "local government policies that promote all-electric new construction."

"PG&E welcomes the opportunity to avoid investments in new gas assets that might later prove underutilized as local governments and the state work together to realize long-term decarbonization objectives," the utility said in a statement.

TWO AGENCIES SUED

Other power companies are defending gas.

Southern California Gas Co., the nation's biggest natural gas utility by sales revenue, sued the California Energy Commission, or CEC, in July over what the utility sees as a bid to marginalize gas.

The lawsuit targeted CEC's 2019 Integrated Energy Policy Report, a planning document. It argued that the agency failed to take a full look at natural gas in its report and omitted submitted comments. The result was to minimize the role of natural gas, the suit said, noting that other agencies rely on the state commission's assessment.

"California law requires the CEC to implement a balanced approach to California's complex energy needs that includes the use of natural gas," it said.

Meanwhile, the California Natural Gas Vehicle Coalition, funded in part by SoCalGas, sued CARB over its Advanced Clean Trucks regulation.

That rule required medium- and heavy-duty vehicle manufacturers to sell an increasing percentage of zero-emission trucks starting in the 2024 model year. The suit claimed that the rule would create "significant, short-term environmental impacts" by spurring construction of infrastructure to support new hydrogen fueling and electric vehicle charging stations.

SoCalGas, a subsidiary of Sempra Energy, did not respond to requests for comment on the building code update.

The California Building Industry Association hopes to shape the timing of natural gas restrictions. Raymer argues that state officials need to allot more time for developers and heat pump manufacturers and installers to shift toward electrification of buildings.

Heat pumps currently make up about 2% of residential heating units, he said. When the solar mandate took effect, solar was being installed on about 25% of homes, Raymer said.

California "has made it very clear it's decarbonizing, and that means both the new and existing housing stock is going to go through some major changes, the same thing for the commercial stock," Raymer said. "We get that."

But he said requirements to use heat pumps instead of gas appliances could increase costs for developers. CEC could offer builders an optional all-electric package that includes "slightly less stringent" energy efficiency requirements on attic and wall insulation.

That could "save the builder a small amount of money that can be used in making the switch away from gas to electric," Raymer said.

ARCHITECTS AND DOCTORS

Architect Scott Shell said heat pumps are a known technology that are used all over the country. Installers are familiar with the equipment, he said, because it's roughly the same technology as air conditioners.

He's a member of the American Institute of Architects in California, whose board voted unanimously in 2018 to support a national and international energy standard that aims for carbon neutrality in new buildings.

The building industry's contention that heat pumps can't be widely used is "the weakest part of their argument," Shell said.

Electrification is also less expensive, he said. The University of California recently opted for all-electric buildings in its new student housing projects because those bids were the least expensive, he said.

"Anytime anybody has to do something a little bit different, there's a learning curve," Shell said of all-electric homes. "I don't think that learning curve is going to be any different three years from now. I don't think putting it off is going to help with that."

Many health professionals also support electrification.

Lisa Patel, a pediatrician at a San Francisco hospital, said children living in homes with natural gas cookstoves have a 24% higher risk of being diagnosed with asthma over their lifetimes and a 42% higher risk of experiencing asthma symptoms.

"I'm constantly struck by the fact that I've been living with gas stoves in my home for years," she said. "As a doctor, I should have known better. ... So now that I know, I want to make as many other people know and that we really work toward getting these out of our homes."

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