If you break down your home energy use by appliance and use, the chances are that heating water comes in second only after heating your home. Estimates put water heating at 380-500 kWh / month, which is probably around 10-15% of your total home energy use provided you use electricity to heat and cool your house. If not, your water heater is an even larger share of your power bill. I’ve written about saving energy with your choice of appliances and fighting vampire electricity use with smart plugs, and those things save a little power at the margin. Your choice of water heater can make a much bigger difference.
Hybrid water heaters employ the same technology as a home heat pump, meaning that they remove heat from the air and put it into the water, much like an air conditioner. In addition, hybrid water heaters have a conventional heating element and can function like an ordinary water heater if the temperature is low enough.
According to Rheem, the manufacturer of the most efficient hybrid water heater available in the USA, a hybrid water heater can use as little energy as a 100 watt incandescent light bulb, which amounts to about 75% less power than a conventional electric water heater. By replacing a conventional water heater with one of these, you can cut electricity use by 75% save yourself nearly $500 / year, depending on where you live. Rheem even has a handy calculator showing how much you can save and how long it will take you to earn a return on investment.
There are a few considerations to keep in mind when switching:
- Where does your water heater sit in your home? Since this effectively acts as an air conditioner, you’ll need to consider its effects on the area around where it sits. If you live in a cold climate, the ideal location would be a basement where you don’t spend too much time. In this case, the water heater may make use of the waste heat of some of your other appliances, like your dryer. You may want to insulate your basement a little better both to block the noise and keep the cold air out of the rest of your house. If you live in a warm place, on the other hand, the built in AC will be awfully nice.
- What size of water heater will you need? There are handy guides out there, and if you find yourself depleting the hot water supply quickly and need to heat water for high demand, your water heater will kick into high demand mode and the efficiency benefits will be greatly lessened. However, there are certainly ways to reduce how much water you use. The two no-brainers are installing watersense shower heads and washing your clothes with cold water. I find that our family of 4 does just fine with a 50 gallon tank for these reasons.
- Can you program your heater, or monitor your energy use from day to day? New water heaters come with apps. You can program your appliance to have a supply of hot water when you typically need it (whenever you take a shower) and a minimal supply when you don’t (in the middle of the night.) You can also optimize your energy use so you heat your water in the low parts of the duck curve , effectively making it a store of energy to optimize the use of renewables. Not only that, but you can put it in vacation mode when you go out of town and turn it back on when you are headed back home.
- What else can you do? Depending on how your house is arranged, you may be able to get even more efficient (and get by with a smaller water heater) by using drain water heat recovery. This requires the drain to be just above the water heater, so it may not work for retrofitting an old house like mine.
After a little geeking out, I settled on a regular schedule for my heater. It heats the water up to 120 around 3:30am-9am and 125 from 3:30-9pm. Yes, 125 is 5 degrees over the maximum recommended temperature, but we’ve never burned ourselves and I find this helps provide enough hot water for a few showers and running the dishwasher. Overall I find our new water heater works great – water supply and pressure is good and our home electricity bills have dropped as expected.