Planet Earth

Climate-Friendly Water Heating

A Santa Clara County Guide

Frequently Asked Questions

Here are diverse questions that we've heard multiple times about installing a heat pump water heater.

Can the grid cope with extra power demands?

Yes. The California grid is only ever under stress on hot summer evenings, when solar dies down and air conditioning stays on. You can program your heat pump water heater to heat up earlier in the day when there is excess power and avoid the evening rush, which actually helps the grid.

Are heat pumps new-fangled and unreliable?

Heat pump water heaters have been around since the 1950 and most of the current manufacturers have been making similar models since about 2010. The heat pump water heater market size was estimated at about $2.1 billion in 2021, and it is growing fast. Most heat pump water heaters have a 10-year warranty, compared with 6 for most gas heaters, suggesting that they are more reliable than gas.

Are the numbers on this website accurate?

Yes and No. We've done our best to keep the numbers representative and accurate, but everyone's situation is quite varied - living alone vs. having 3 shower-mad teenagers, big or small house, different rate tariffs all impact your usage and savings, while the state of the house and electrical panel may have a big impact on the cost of installation. So these numbers are meant to be typical, but won't be accurate for everybody.

What if I'm a renter?

You'll need to find some way to split the costs and benefits with your landlord. We're hoping to later create a template that will help with that, but in the meantime, maybe just show them this site and suggest that you'd be willing to pay a little more in rent if your bill goes down even more - and let us know how that conversation goes!

Are heat pumps noisy?

Sometimes, but mostly not. The compressor and fan are said to sound about as loud as a refrigerator or dishwasher, but some people do find them louder. If your water tank is in the garage, you probably won't notice, if it's close to living quarters, then be careful if you use Rheem models. Although they are advertised as among the quietest, some 2021 units got complains for excessive noise, and it's not clear if that is still true for 2022 units, or how extensive it is.

My plumber says I should install gas. Should I trust him?

Most plumbers want to stick with what they know, and they don't want the hassle of also dealing with electrical work. They will be very expert on some issues, like situating the heater, clearance etc. but might not have enough experience with heat pumps, or have heard too many rumors to fully trust on the overall issue. BayREN contractors generally have good heat pump experience, but you should check how many they have actually installed, and call around to find someone who is comfortable with heat pump installs.

What about tankless water heaters?

Tankless gas heaters are more efficient than regular gas heaters, but have almost twice as much methane emissions, making them only marginally less polluting. Tankless electric heaters are far less efficient than heat pumps and usually work out to be very expensive to run.

What's a mixing valve? Should I get one?

Water heaters typically heat the water to about 120 °F. You can run it hotter, up to 140 °F, and then use a mixing valve to mix in cold water to bring the temperature down before circulation. This increases the amount of hot water the tank can deliver, by about 25%, so allows you to use a smaller tank, or give you a safety net if you buy a small tank and later want to upsize. It also better protects against scalding or the rare chance of Legionella growing in your water tank.

Can I use a recirculation pump with a heat pump?

Recirculation pumps move hot water through your pipes continuously, for instant hot water. They are huge energy hogs, both for the electricity they use and because your hot water is constantly cooling by going through all your piping. Heat pump water heaters also don't really like recirculation pumps because they are programmed to have cold water, not slightly cooler water, coming back into the tank. Several different smart recirc pumps are now available, and work with heat pumps. Some just turn on when the water in the pipes is getting cold, others have a button that turns them on when you need a shower, or turn on when you flip the hot tap on and off. Your plumber should know more.


Back to the Santa Clara County Guide to Climate-Friendly Water Heating.