How Long Does a Water Heater Take to Heat Up? By Type

By Ray Bennett · Updated 2 October 2026 · 4 min read · Checked against the sources at the end

How Long Does a Water Heater Take to Heat Up? By Type

Short answer

A.O. Smith says a typical 40 to 50 gallon gas tank heats back up in about 30 to 40 minutes and an electric one in 60 to 90. A 75 gallon gas tank takes closer to an hour, and a 75 to 80 gallon electric tank up to 2 hours. A tankless heater has no recovery time. If yours suddenly takes twice as long, A.O. Smith says something may be wrong.

How long does a water heater take to heat up? It depends mostly on the fuel and the size of the tank. A.O. Smith’s typical figures run from about half an hour for a gas tank to two hours for a big electric one, and a tankless heater has no wait at all.

This page gives those figures, explains why gas is so much faster, and shows what to check when a heater that used to keep up has become slow.

Before you start

What to carry: a torch and your phone, to photograph the rating label for the size and the fuel. Five minutes.

Gas or electric? This is the question that matters most here. A.O. Smith says gas reheats 2 to 3 times faster than a standard electric tank, because the burner puts in far more heat.

Know what you are timing. A.O. Smith’s figures are for heating a tank back up after the hot water has run out, not for filling a new one.

Before you wait it out. Twice as long is a fault. A.O. Smith says that if a water heater suddenly takes twice as long to recover, something might be wrong.

Full before power. After a tank has been drained, fill it completely before the power goes back on. GE says elements are damaged if they run without water.

If you smell gas. Leave the house and call from outside. Do not light anything or touch a switch.

Typical times, by type

A.O. Smith's typical figures for heating a tank back up once the hot water has run out.

Check 1

Find your heater on the chart

Gas tanks. A.O. Smith says a typical 40 to 50 gallon gas tank fully recovers in about 30 to 40 minutes, and a 75 gallon one closer to an hour.

Electric tanks. A 40 to 50 gallon electric tank takes 60 to 90 minutes, and a 75 to 80 gallon one up to 2 hours. A.O. Smith says that is why families with electric heaters often space out showers and laundry.

Tankless. A.O. Smith says there is no recovery time, because it heats water as it flows. You still wait a few seconds for hot water to travel through the pipes.

Heat pump water heaters. A.O. Smith says their reheat time varies with the operating mode: a heat pump water heater not heating.

Why gas is faster

The heat going in decides the speed. A gas burner puts in more than twice what a standard element does.

Check 2

Compare the heat going in

The burner and the element. A.O. Smith says a typical gas water heater has a burner of around 40,000 BTU, while a standard electric one runs at 4,500 watts, roughly 15,000 BTU. By the Energy Information Administration’s 3,412 BTU per kilowatt hour, 4,500 watts is 15,354 BTU an hour.

The recovery rate. Bradford White says recovery is the number of gallons a heater can heat in an hour, and that it depends on the tank, the heat source and the size of the burner or element. A.O. Smith gives gas tanks 40 to 50 gallons an hour and electric tanks 15 to 20.

A bigger burner. A.O. Smith says a 50 gallon gas heater with a 40,000 BTU burner recovers in about 35 minutes, and a 50,000 BTU model in around 28.

What slows it down

Check 3Free to a service visit

Rule out the usual causes

Cold water coming in. A.O. Smith lists the incoming water temperature among the things that set the heating time, so a tank is slower in winter.

Sediment and corrosion. A.O. Smith says a lack of maintenance, sediment and corrosion lead to longer heating times: sediment in a tank.

An element that has failed. An electric tank with a dead element heats slowly or runs out early: testing an element.

Too small a tank. If the household has grown, the heater may simply be outrun: what size water heater you need.

When to stop waiting

Check 4Free to check

Know when it is a fault

No hot water at all after the normal time. Start with the checks for a gas or electric tank that is not heating: a water heater with no hot water.

Hot at first, then cold fast. The shower checks are here: a shower that goes cold.

A pilot that keeps going out. A gas tank cannot heat without it: a pilot that will not stay lit.

Questions people ask

How long does it take a gas water heater to heat up?

A.O. Smith says about 30 to 40 minutes for a typical 40 to 50 gallon tank, and closer to an hour for a 75 gallon one.

How long does an electric water heater take to heat up?

A.O. Smith says 60 to 90 minutes for a 40 to 50 gallon tank, and up to 2 hours for a 75 to 80 gallon one.

Why does my water heater take so long to heat up?

Cold incoming water in winter, sediment in the tank, a failed element on an electric heater, or a tank too small for the household. A.O. Smith says twice the normal time points to a fault.

How long after installing a water heater can I use it?

A.O. Smith says a gas tank heats from empty in about 30 to 40 minutes, and most electric units in around 60 to 80 minutes.

Does a tankless water heater need time to heat up?

No. A.O. Smith says it heats water as it flows, so there is no recovery time, only the few seconds for water to travel through the pipes.

What does recovery rate mean?

Bradford White says it is the number of gallons a heater can heat in an hour. A.O. Smith gives gas tanks 40 to 50 gallons an hour and electric tanks 15 to 20.

Sources: A.O. Smith "How Long Does It Take a Water Heater to Heat Up?", "How Long for a Water Heater to Reheat After Use?" and "How Long Does It Take for a Water Heater to Heat Up?", Bradford White "What does recovery mean for my water heater?", and the U.S. Energy Information Administration "British thermal units (Btu)"