Smart control for an electric water heater

Know your water heater first

Look at the nameplate on the tank for voltage and wattage. If it lists 240 V, never use a 120 V smart plug on it, and never adapt one.

Step 1: Check the temperature setting

This is free and does more than a timer on many tanks. ENERGY STAR’s guidance says most households only need the thermostat set at 120°F, compared with a factory default that is often higher. Water heated to 140°F poses a scalding risk. The same guidance notes a very slight risk of promoting Legionella bacteria at 120°F, which it describes as still considered safe for the majority of the population, and suggests mixing valves for households with immune-compromised members. If someone in your home has a weakened immune system, ask a doctor or plumber before lowering the setting. Some dishwashers without a booster heater may need 130–140°F water.

For long absences, the same source says to turn the thermostat down to the lowest setting or turn the water heater off completely. Many models have a vacation mode that does this and restores the temperature on a set date.

Step 2: Does a timer save energy?

A well-insulated tank loses little heat, so a timer that switches it off overnight saves less than you may expect, and it can leave you without hot water. The savings are largest in two cases:

• Time-of-use rates. The Energy Information Administration notes that demand and costs peak in the afternoon and early evening. If the tank is hot before the peak window and the elements stay off during it, a family can use stored hot water during the peak. See time-of-use rates and your smart home.
• Long absences. Turning the temperature down or off while away avoids keeping 40 or more gallons hot for nobody.

Size matters. A schedule that works with a 80-gallon tank may run out of hot water with a 40-gallon tank. Test it with your actual showers and laundry before you leave it on.

Option A: a heat pump water heater

The Department of Energy says heat pump water heaters can be two to three times more energy efficient than conventional electric resistance water heaters. They pull heat from the air around them, so the room must stay between 40°F and 90°F year-round and have at least 1,000 cubic feet of air space. ENERGY STAR lists certified models, including a 120 V, 15 A circuit variant. Most have operating modes (efficiency, hybrid, electric only, vacation) and Wi-Fi apps. If your tank is near the end of its life, this is the upgrade that usually matters more than any controller.

Option B: a smart controller on an electric tank

Add-on controllers sit in the 240 V supply or at the breaker. They need the right rating (higher than the heater’s amps), a certified relay and proper wiring. The job involves 240 V in a panel, so use a licensed electrician and follow local code. Turn off the breaker, verify that the power is off with a tester, and label the circuit. A controller that disconnects the heater at the wrong time can also trip safety devices, so use one made for water heaters and follow its instructions.

Utilities sometimes provide load-control switches or rebates for water heater control programs. Ask yours before you buy hardware; the savings may come as a bill credit.

Option C: gas water heaters

Do not modify the gas valve, igniter or thermostat control yourself. Gas work needs a licensed plumber or HVAC technician. Use the heater’s own vacation or away setting, and consider a leak sensor and a carbon monoxide alarm nearby. See where to put carbon monoxide detectors.

A cheap, useful addition: a leak sensor

A tank that fails can release dozens of gallons. A $15–$35 leak sensor in the drain pan gives early warning that no schedule can. See the water leak protection kit.