Water Heater Questions and Answers

Turn off the gas or power, close the cold-water supply, attach a hose to the drain valve and run it outside, open a hot tap, then open the drain and let it run until the water is clear. Close the drain, refill until a hot tap runs steadily, then restore heat. DOE suggests draining a quart every 3 months to remove sediment.

Installed, a standard 40- to 50-gallon tank runs about $600 to $3,100 nationally, according to HomeGuide's 2026 figures, and Angi's 2026 average is $1,334. Tankless units run $1,400 to $5,600. Heat pump water heaters cost more; SMUD customers paid a median $6,210 for gas-to-electric installs before rebates of up to $4,000.

Shut off the heat and close the cold-water supply. Let the water cool if you can. Connect a hose to the drain valve, open a hot faucet to let air in, and open the drain valve until the tank is empty. If the flow stops early, sediment may be clogging the valve; a plumber can clear it without damaging the valve.

DOE says most storage water heaters last 10 to 15 years and tankless units can last more than 20 years. A DOE-funded sizing tool from Pacific Northwest National Laboratory assumes an average life of 13 years for storage water heaters. Hard water, sediment, high pressure and a used-up anode rod all shorten tank life.

National guides put installed cost at $1,400 to $5,600 (HomeGuide) or an average of $2,631 (Angi, 2026). Switching from a tank costs more than replacing an existing tankless unit, because of possible gas line upsizing ($350 to $750), new venting ($500 to $1,500) and extra labor. SMUD does not list rebates for gas tankless units.

When a hot tap opens, a flow sensor detects water moving through the unit and fires a gas burner or electric element, which heats the water as it passes through a heat exchanger. When the tap closes, heating stops. Units need a minimum flow, 0.4 to 0.9 gallons per minute per a DOE guide, before they fire.

Match the heater's first-hour rating to your busiest hour of hot water use. DOE's worksheet uses about 20 gallons per shower, 7 per dishwasher load and 25 per top-loading washer load. A household with two showers and a dishwasher in its peak hour needs a first-hour rating of at least 47 gallons. HomeGuide describes 50-gallon tanks as typical for 3 to 4 people.

It is an electric water heater that uses a refrigeration cycle, like a refrigerator in reverse, to move heat from the air into the tank. ENERGY STAR says certified models use 70% less electricity than standard electric models. Most have backup electric elements for heavy demand, and they need a space that stays between 40°F and 90°F.

It depends on tank size and recovery rate. The first-hour rating on a tank's EnergyGuide label shows how many gallons of hot water it can deliver in an hour from full. Heat pump water heaters recover more slowly in heat pump mode, especially with cold winter inlet water, according to DOE guidance. Tankless units heat water as it flows.

For gas, turn the control knob to OFF; many models also have a PILOT or VACATION setting for short absences. For electric, switch off the water heater's breaker. If there is a leak, also close the cold-water supply valve above the tank. If you smell gas, do not touch the heater: leave and call 911, then PG&E.

Follow the manufacturer's manual. Descaling usually means closing the unit's service valves, circulating the descaling solution the manufacturer specifies through the heat exchanger, and flushing with clean water. A DOE guide says recommended frequency ranges from twice a year to once every three years, depending on the model and water hardness.

Common sources are loose connections at the top, a relief valve opening because of high temperature or pressure, a worn drain valve at the bottom, or a corroded tank. Leaks from fittings and valves can usually be repaired. If water comes from the tank body itself, the heater needs replacing; HomeGuide puts that at $600 to $1,800 nationally.

First make sure the tank is full: open the cold-water supply and run a hot faucet until water flows steadily without sputtering. Then relight a gas pilot following the label on the tank, or switch an electric heater's breaker back on. PG&E advises waiting five minutes after shutting off gas to a pilot before relighting.

Add up the gallons per minute of fixtures you run at the same time and the temperature rise from your coldest incoming water to the temperature you want. A DOE guide lists typical flows of 2.5 gpm for a shower, 2.5 for a kitchen sink and 1.9 for a dishwasher. Two showers and a sink need about 7.5 gpm at your required rise.

Many electric water heaters have a reset button on the high-temperature cutoff behind an access panel. Switch off the breaker before opening the panel, since the wiring is live, then press the button and restore power. If it trips again, a thermostat or element has likely failed. Gas water heaters do not have this button; a pilot that goes out needs relighting.

Cold water enters through a dip tube to the bottom of the tank, where a gas burner or electric elements heat it. Hot water rises and leaves from the top when you open a tap. A thermostat keeps the tank at its set temperature, and a temperature and pressure relief valve releases water if the tank gets too hot or pressure gets too high.

HomeGuide says a standard tank replacement takes 2 to 6 hours and a tankless installation 6 to 10 hours. Heat pump water heaters can take longer, and ENERGY STAR notes your installer may need time to order the right model. A permit inspection is scheduled separately by your city or county building department.

It is a safety valve that opens to release water if the tank overheats or pressure gets too high, preventing a dangerous failure. California's plumbing code requires its drain line to run to the outside of the building and be no smaller than the valve outlet. Never cap or plug it. A dripping valve needs a plumber to find the cause.

California Plumbing Code section 608.3 requires an expansion tank or approved device when the water system has a check valve, backflow preventer or other normally closed device that keeps heated water from expanding back into the main. Roseville's building division says the code calls for one on water heating systems. National installed costs run about $90 to $400.

A licensed contractor, in most cases. CSLB says unlicensed people may do jobs under $1,000 only if the work needs no permit and they have no employees, and water heater replacements need permits. CSLB's C-36 Plumbing Contractor classification covers installing equipment that heats water. Check any contractor's license on CSLB's free lookup.

Because hotter water burns quickly. The CPSC says most adults suffer third-degree burns in 2 seconds at 150°F, 6 seconds at 140°F and 30 seconds at 130°F, and that even 120°F water can burn after 5 minutes. CPSC urges a 120°F setting, which also saves energy; DOE calls it safe for most people.

Yes, if its venting fails. The EPA lists back-drafting from gas water heaters among indoor carbon monoxide sources, with symptoms like headaches, dizziness, nausea and flu-like symptoms that clear up after leaving home. California law requires CO alarms in homes with gas appliances. If an alarm sounds, get everyone outside and call 911.

Some are. SMUD offers up to $4,000 for replacing a gas water heater with a qualifying heat pump model and $1,000 for replacing an electric one. Roseville Electric offers $2,500 and $1,000. The federal 25C tax credit ended December 31, 2025, TECH Clean California's single-family incentives are fully reserved, and Golden State Rebates' retail offers have ended.