Heat Pump Water Heaters
see also note on hot water recirculation systems, near bottom of this page.

Natural gas burning water heaters have been the most popular type in California for greater than the past half century.  This is because, until recently, the only alternative to gas water heaters - electric resistance water heaters - cost around four times as much to operate.  Because standard electric ("electric resistance") water heaters are so energy wasteful, the CA energy code (Title 24) does not allow them except where they are replacing a like unit.

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The good news is that there is a technology that can heat water efficiently and economically, without relying on fossil fuels!  The technology is called a Heat Pump Water Heater, or HPWH.  This is a relatively new technology for heating water, but is technologically proven, and increasing in popularity.  My family replaced our natural gas water heater with a HPWH in December 2021, and are happy with this upgrade.  Using heat pump technology to heat water is a variation on the heat pump technology used to provide space heating and cooling, which has been around for many decades.

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HPWH Considerations:

• Electrical Requirements:  Most HPWHs are 240 volts, which draws a lot of amps.  A home's electric service and electric panel may, or may not, have adequate amps to accommodate a new 240 volt HPWH.  If the available amps is inadequate, there may be ways to reduce amp requirements at other electric devices to free up available amps.  If not, and the current home amperage is inadequate, and a 240 volt HPWH is desired, then a service and panel upgrade would be required.

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• Voltage:  As noted above, most HPWHs are 240 volts.  This high voltage is necessary to power electric resistance heating, which operates when the air temperature is too low for the heat pump portion of the system to function effectively.  However, in 2022 Rheem introduced a few 120 volt HPWH models.  These do not include electric resistance heating, and therefore are not meant to be used in climates that experience much freezing weather.  Rheem rates these models to be acceptable for most of California (excepting the Sierras and the far Northeast corner of the state).  These water heaters plug into a standard 120 volt receptacle (240 volt HPWHs need to be "hard-wired" to a 240 volt circuit).  120 volt water heaters are very unlikely to require an electric service upgrade.  Note that Rheem makes both "shared circuit" and "dedicated circuit" models.  The dedicated circuit model produces hot water at a more robust rate.  However, installing such a water heater would require a dedicated circuit for only the water heater, which would also involve a new breaker for that circuit in the electric panel.  This electrical upgrade would be less costly than adding amperage to one's electrical system for a 240 volt HPWH (see first point above).  As swapping existing gas water heaters for new HPWHs becomes more popular, and with new mandates, expect to see more manufacturers offering 120 volt HPWHs.

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• Capacity:  As with any water heater purchase, size/capacity/hot water volume is always important.  You don't want to be caught short of hot water, but you also don't want to pay for more water heater, nor use more energy to heat the water, than necessary.  We had a 40 gallon gas water heater, which was fine for our needs.  However, our new HPWH is 50 gallons because (as explained by HPWH dealers) HPWHs heat water a bit more slowly than gas water heaters do, so having a modest increase in stored hot water can be beneficial.  HPWHs are very well insulated to reduce tank heat loss, thus needing less energy to keep the stored water hot.

 

• Location: HPWHs exhaust cool air (due to the process of recovering warmth from the air to heat the water).  HPWHs are often located in a garage.  They may be located in a crawl space, or in attic space (if structural concerns and leak drainage are addressed).  Because the heat pump exhaust cool air, and the heating efficiency is reduced in colder air, it is important for the HPWH to be in a large space.  If the HPWH must be located in a smaller space (e.g. a utility closet accessed from the outside), then it is imperative that the exhaust air be ducted to the outdoors.  Otherwise, the space the water heater is in will be so cold as to significantly reduce its efficiency.  Even if the HPWH is located in a large space, like a garage, ducting the exhaust to the outdoors would improve its energy-efficiency.  But in a larger space, where the cold air exhaust won't impact the air temperature as much as it would in a small space, the payback in energy cost savings for adding this feature may take a long time.  In our case, the cold exhaust would have been near our front door, not exactly a welcome location for visitors!  Our HPWH installer told me that they have never done a HPWH installation with a ducted exhaust, likely due to cost and practical considerations.  Our plumber said that we would have to hire an HVAC company to install a ducted exhaust. That said, if you can afford to install an exhaust, and have a good outdoor wall location for the exhaust register, consider doing so to make your new water heater even more energy-efficient.  Note: The energy code does not allow water heaters to be outdoors.

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• Energy Efficiency / Energy Code Compliance: Like installing new space conditioning equipment, new water heater installations are supposed to be done under a building permit, and must meet applicable energy and plumbing codes.  While HPWHs sold in CA likely meet energy code efficiency requirements, it's best to check - and choose one of the higher efficiency models if possible.  To meet energy code energy efficiency, electric water heaters (except those that are replacing electric water heaters) must be HPWHs that meet the Northwest Energy Efficiency Alliance (NEEA) HPWH Tier 3 (or higher) rating (or meet other efficiency requirements if Tier 3 is not met).  The NEEA HPWH ratings are found at https://neea.org/img/documents/HPWH-qualified-products-list.pdf . The HPWH efficiency requirement is found in the CA Energy Standards. Alteration project HPWH requirements are at Section 150.2 (a) 1. D. ii., which is on page 348 (new construction HPWH requirements are basically the same).  The Energy Standards are available at https://www.energy.ca.gov/publications/2022/2022-building-energy-efficiency-standards-residential-and-nonresidential .  The link to the PDF document titled, Commission Final Report: 2022 Energy Code, is at the bottom of the page.

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• Noise: When in heating mode, HPWHs do create some noise - similar to that of the outdoor unit of an air conditioner, although not as loud. HPWHs have sound ratings.  If you are sensitive to sounds, choose a quieter model, and if possible do not attach the tank to an interior wall (i.e. if in a garage, attach it to a side wall if possible).  Our new HPWH is attached to the garage side of our powder room wall, so the sound is somewhat loud in that room when the heat pump is operating.  However, we find that almost the only time the heat pump motor/pump/fan system operates is during hot water use - and for a while after until the tank's water is hot again.  The great majority of the time, our water heater is quiet. 

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• Condenser Water:  Like all heat pumps, a HPWH generates a small amount of condenser water.  This must be drained someplace.  In our case, a pump was already nearby for the AC system condenser water coming from the AC coils in the furnace.  The HPWH installer simply piped the water heater condenser water to that same pump (which pushes the drain water to the backyard).

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​INCENTIVE PROGRAMS (ways to save on your water heating system upgrade): 

• BayREN offers $1,000 for installing a new HPWH - but only if a contractor approved by BayREN does the work. Go to https://www.bayren.org/ , click Rebates & Financing, then Homeowners / Heat Pump Water Heaters. Also see Incentive Programs on the Low Cost Actions page of this website for more information about BayREN.

 

• PG&E no longer offers $300 rebates.  However, on their rebates page (from the PG&E home page, choose Save Energy & Money, then Savings Solutions & Rebates, then Rebates by Product), you will find a link to Golden State Rebates, which offers $500 rebates for certain HPWHs when replacing any electric resistance water heater, or replacing a 40 gallon gas water heater.

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• The Switch is On, at https://switchison.org/ , is another good resource for financial incentives to switch from gas to electric systems, including HPWHs.

 

Of course, the above rebate amounts may change.  Check with these organizations for current rebates and qualifications.

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