How Long Does a Water Heater Take to Heat Up?

The Short Answer: A typical 40-gallon gas tank reheats a full tank of cold water in about an hour, and a 50-gallon in about 1¼ hours; the burner recovers around 40 gallons per hour. A standard electric tank recovers about 21 gallons per hour, so a 50-gallon tank takes about 2½ hours. A heat pump tank on its compressor alone can take around 8 hours, longer in a cold room. Tankless heaters don’t need to heat up.

Recovery rates from the spec sheets

Manufacturers rate recovery as how many gallons the heater can raise by 90°F in an hour. That’s a cold-water case: for example, incoming water at 40°F heated to 130°F. Divide the tank size by the recovery rate to get the time to heat a full tank from cold.

The gas figures come from A. O. Smith’s GCR spec sheet (opens in a new tab) (42 and 43 gallons per hour at 40,000 BTU/h), Bradford White’s gas spec sheet (opens in a new tab) (43 gallons per hour), and Rheem’s Performance gas sheet (opens in a new tab) (36.4 gallons per hour at 36,000 BTU/h). The electric figure is the same on Rheem’s electric spec sheet (opens in a new tab), A. O. Smith’s ENT models (opens in a new tab) and Bradford White’s electric sheet (opens in a new tab). The heat pump figures are for Bradford White’s 50-gallon AeroTherm G2 (opens in a new tab), rated at 67.5°F room temperature.

In summer, when the incoming water is warmer, the rise is smaller and recovery is quicker.

Why gas is faster than electric

A 40,000 BTU/h burner puts heat into the water about twice as fast as a 4,500 W element. Most household electric tanks are also wired non-simultaneous: only one of the two elements runs at a time. Bradford White’s sheet notes that when both elements run together, recovery roughly doubles. The standard ratings assume one at a time, and changing the wiring is an electrician’s job that depends on the circuit.

Heat pumps depend on the mode

A heat pump water heater moves heat from the surrounding air, which is efficient but slow. On the AeroTherm G2, the compressor alone recovers about 6 gallons per hour, while compressor plus element recovers about 24. Run in an efficiency or heat-pump-only mode, a heat pump tank can take many hours to recover after heavy use. In a hybrid or high-demand mode, it uses the element when needed and recovers about as fast as a standard electric tank. A cold room also slows the compressor. See heat pump water heater sizing and location.

First-hour rating: how much you get before running out

The first-hour rating on the label and spec sheet is the better guide to running out. ENERGY STAR (opens in a new tab) defines it as the most hot water a storage heater can supply in an hour, starting with a fully heated tank. It combines the tank size and the recovery rate, measured at a 125°F outlet temperature.

That’s why the 40-gallon gas tanks above are rated at about 68 to 80 gallons in the first hour, while 40-gallon electric tanks are rated at about 48 to 54. Both start with 40 gallons, but the gas burner refills faster while you use it.

New or refilled tank

After a new installation or a drain and refill, the whole tank starts cold. A. O. Smith’s electric manual (opens in a new tab) says a tank of cold water may take several hours to heat. Its electric and gas (opens in a new tab) manuals both say that if there’s no hot water at all after two hours, something needs troubleshooting.

• Electric: the tank must be completely full before the power goes on. Powering an element in an empty or partly filled tank burns it out. See water heater turned on without water.
• Gas: make sure the pilot or burner actually lit. See brand new water heater no hot water.

When it’s taking too long

• Gas tank, nothing after two hours: check whether the pilot is lit and whether the status light shows a fault. See gas water heater burner on but no hot water.
• Electric tank lukewarm, or running out faster than it used to: a failed lower element or thermostat often leaves only the top of the tank heated. See water heater element not working.
• Water was hot yesterday and now recovers slowly: sediment on the bottom of a gas tank, a low thermostat setting, or a dip tube problem can all reduce output. See no hot water.

Tankless heaters

A tankless heater doesn’t store water, so there is nothing to heat up. Hot water should arrive as soon as the water in the pipes between the heater and the tap has run through. If it takes much longer, see tankless water heater takes a long time to heat up.

Frequently Asked Questions

Q: How long after a shower before there’s hot water again? A: You don’t need a full recovery. At the rated 90°F rise, a gas tank reheats roughly 10 gallons in 15 minutes and an electric tank roughly 5. Warmer incoming water shortens that.

Q: Will turning the thermostat up make it heat faster? A: No. The burner or element heats at the same rate; a higher setting only makes it heat for longer. It raises the scald risk and doesn’t fix a slow recovery caused by a failed part.

Q: Why does my electric water heater take longer in winter? A: The incoming water is colder, so each gallon needs more heat. Rheem’s electric troubleshooting chart (opens in a new tab) says colder winter inlet water is normal and takes longer to heat.