How Long Does It Take For a Water Heater to Heat Up?

Starting a chilly day with a quick hot shower is no less than a blessing to make your day superb. 

The first question that hits our mind is the time a water heater takes to heat up the water when you are looking for tank water heaters or tankless models. There are many factors that affect the water heating time including different models of water heaters and the distance of the device from the water fixtures. 

how long does it take for a water heater to heat up

In addition to this, their sizes vary depending on the model, so it is vital to know how long you must wait when the supply runs out. Generally, the water heater’s usual capacity is 40 gallons. If it is a gas heater, it normally takes 30 to 40 minutes to be fully heated.  For an average electric heater, it is approximately an hour and may be 20 minutes above which is twice the gas heaters’ timing. 

How Long For Water Heater to Heat Up

In general, larger heaters require longer time to heat the water. Apart from this, different models take different time to warm the water.  Also the water heaters powered by different fuel type such as liquid propane, natural gas and electricity have different timing to heat the cold water.

How Long Does It Take a Gas Water Heater to Heat Up?

Gas hot water heaters run more efficiently and heat water more quickly than electric models. At the bottom of tanks, powerful burners burn natural gas as fuel for heating water. 

Heat-up times for gas water heaters depend on their temperature setting and the temperature of the cold water they are supposed to heat. Below you will find some averages:

  • 30 to 40 minutes for a 40-gallon gas water heater
  • 40 to 50 minutes for a 50-gallon gas water heater
  • 60 to 70 minutes for a 80-gallon gas water heater

For these calculations, a temperature of 62° is assumed.

Going further, the gas boilers provide the fastest, most efficient, and most traditional way to heat water in a residence. The use of gas as a power source has been popular for decades. One of the advantages is the lower energy bills it brings. 

Obviously, the tank size of the heater has a major impact on the time it takes to heat more water. The BTU (or British Thermal Unit) rating of the heater is the next major consideration. In other words, a BTU is what it takes to raise a pound of water by 1- degree  Fahrenheit. More BTUs can result in faster water heating.

In the US, the average hot water heater tank holds 40 gallons. We can estimate that the water count in the example tank is approximately 330 lbs. Thus, every gallon of water weighs approximately 8.3 pounds.

               330 lbs of Water = 40 Gallons x 8.3 lbs Per Gallon

Suppose the temperature of the water is 60 degrees and you want it to reach 120 degrees. A rise of 60 degrees will make the water reach 120 degrees.

We could calculate thermodynamically based on 40,000 BTUs and a 40 gallon tank, however, we can simplify it and say it takes one half of one minute to heat each gallon, which equals about a half hour to heat up the tank.

Having a lower BTU rating or a smaller tank will reduce the time it takes for your hot water heater to warm up. If, however, your tank is large or has a lower BTU rating, it will take longer for its heat to reach your desired temperature.

Keeping these specifications in mind will help you choose a water heater that will heat up your water within the time frame you prefer (after it runs out of hot water) and will store plenty of hot water.

Gas water heater buying suggestion

In addition, remember that this is the time it takes to heat up new cold water in your water heater tank. Once you have stored hot water in the tank, it does not take long to start using hot water because the tank stores the pre-heated water.

 It is important to take into consideration how much time it takes to heat up new water once all the hot water in the tank is used up.

gas water heater 40 gallon tank

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How Long Does it Take an Electric Hot Water Heater to Heat Up?

When compared with gas-fired water heaters, electric tank water heaters usually take twice as long to heat. Even though electric elements are usually more economical, they can’t compete with gas fired systems when it comes to performance.  For an electric water heater to heat a 40-gallon tank, it would take about one hour from the moment fresh water is pumped into the tank.

Heat up times for electric water heaters are longer than for gas heaters. In this type of unit, heating is achieved by immersing electrical heating elements within the tank.

Heating element wattage and the desired temperature for water heater determine the length of time it takes to heat water. 

How To Adjust The Temperature On Electric Water Heater

The below averages, however, should be helpful:

  • 60-80 minutes for a 40-gallon electric water heater
  • 145-150 minutes for a 50-gallon electric water heater
  • 120-130 minutes for an 80-gallon electric water heater

With a 40-gallon electric water heater that is set at 120 degrees and takes 5500 watts to heat up, you can expect it to take about an hour to an hour and 20 minutes.

In an electric 50-gallon tank, the heat will take about an hour and 45 minutes to reach the appropriate temperature. Typically, it takes two hours for a large, 80-gallon electric water heater to heat up the water. 

Because of this, homes with more water usage generally opt for gas water heaters rather than electric ones. Models that run on electricity are perfect for small homes and low water usage. 

Electric Water Heater, 50-Gallon

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How Long Does it Take a Tankless Gas Heater To Warm Up?

With tankless gas water heaters, your water is heated on demand, so how fast you receive hot water is determined only by how close your heater is to the appliance being used.

tankless gas water heater capacity

In a normal sized home, this should not take more than a few seconds if the system is functioning properly. When traveling through long pipes within a large house, it will take a few additional seconds for the water to reach appliances farther away from the heat source.

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How Long Does it Take a Tankless Electric Heater To Warm Up?

With a tankless electric water heater, your water only begins to warm once you start an appliance. Therefore, before opening the dishwasher or turning on the faucet, the water is not warmed.

An electric tankless heater will usually heat water in minutes, but it will take a little longer than a gas system because gas heat is more powerful.

Electric heaters with tankless technology can heat the water instantly, so it only takes a few seconds for the hot water to reach the fixture after traveling through your pipes. 

6 Factors That Affect How Long A Water Heater Takes To Heat Up

Generally, the waiting time is an estimate only. Water heaters can take a long time to heat up for a variety of reasons. Some of them are common to all types while others are type-specific. 

Let’s discuss each in detail. 

First Hour Rating

The first-hour delivery rating (FHD) is essential in water heaters. When filled with warm water, the FHD indicates how many gallons can be delivered in an hour.

When you have a high FHD rate, you will get hot water more quickly than if you have a low FHD rate. Ideally, a FHD rate of 60 to 80 GPH would be ideal for a unit of 50 gallons. 

In general, a short waiting time is indicated by a high first-hour rating. Fuel source, tank capacity, and size of heating elements or burners play a part in determining the calculation. 

Factors That Affect How Long A Water Heater Takes To Heat Up

Inlet Water Temperature

One of the factors that can seriously affect the recovery time is the inlet water temperature, or temperature rise. It takes a water heater longer to warm water to the desired temperature when the inlet water temperature is low. 

Inlet water in different parts of the country will have different  temperatures. The weather is generally colder in the North than it is in the South. It is common for the inlet water temperature to be around 40 degrees Fahrenheit in colder climates. 50 degrees is normal in warmer climates. To heat water from 40-50 degrees up to 140 degrees, the water heater takes some time.

Generally, we refer to “temperature rise” as the contrast between the temperature of incoming water and the boiler’s preset temperature. It takes longer to heat up inlet water that is colder. 

Water Heater Size

Other factors can slow down water heater heating times, such as the size of the heater. A larger tank requires longer to heat, as we examined in our earlier examples. It’s just a matter of heating up more water.

In terms of how much water can be heated quickly, a storage water heater’s gallon capacity plays a major role. The typical storage water heater keeps approximately 30 to 80 gallons of water. 

In order to speed up the heating process on larger tanks, there will generally be two heating elements or a large burner. In spite of this, smaller tanks warm up faster.

Since fewer gallons are required to heat water in smaller tanks, the water heats up sooner (and runs out sooner). The same thing happens when you heat water in a small 2-quart pot as opposed to a 12-quart stock pot.

In larger capacity gas water heaters, the burner is bigger, which helps them heat up more quickly. If you have a 30-gallon water heater, it will take less time to warm up than a 50- or 80-gallon model.

Fuel Type

Fuel type greatly influences how long it takes to heat up water. In comparison to electric water heaters, gas water heaters heat water much faster. Unlike electric elements, gas burners reach a higher temperature.

It is known that electric water heaters take a long time to heat water. The reason for this is that electrical heating elements are less efficient than gas burners.

FHD rates for 50-gallon gas water heaters generally range from 80 to 90 GPH, while FHD rates for 50-gallon electric water heaters range from 58 to  66 GPH.

For an electric water heater, you will need to wait twice as long as you would for a gas water heater to heat the entire tank.  

Water Heater Type

Water heaters with tanks that store and heat water are called storage models. Tankless models aren’t equipped with storage tanks; they heat the water as it comes out of the faucet.

Both types of water heaters work differently in terms of how fast they heat water. Heat up time for a storage water heater can range from 30 to an hour and a half.

On the other hand, tankless water heaters produce hot water instantly. Overusing hot water will result in a slower flow rate (in gallons per minute), but the water that does come out of the faucet will still be warm.

Recovery Time

The recovery rate of a water heater is the amount of hot water it can provide per hour while it is in use. The recovery rate is the speed with which the water heater can recover (refill) with cold water and heat it again. 

Heating hot water in a unit with a high recovery rate takes less time, so hot water is available faster. Therefore, a water heater with a high recovery rate will be able to quickly heat up the cold inlet water, even if you need a lot of hot water at once.


How long does it take for a 50-gallon water heater to heat up?

An electric hot water heater designed for 50-gallon tanks heats water at 60 degrees in around 1 hour and 20 minutes when the elements are set at 5,500 watts.

Alternatively, a 50-gallon gas unit takes about 40 minutes to get hot.

How long do you have to wait for hot water to come back?

As soon as your tank has run out of hot water, your heater will need to recuperate before it can produce hot water again. A 50-gallon tank requires approximately 20 minutes to fill, and you may have to wait another 20 minutes for the water to heat.

How long can you shower with a 40-gallon water heater?

In the absence of other water appliances with a 40-gallon water heater, you can take two showers in an hour.

How long does it take for an 80 gallon water heater to heat up?

About 60 to 70 minutes are needed for a large 80-gallon gas water heater to heat up.

Daniel Adley is a seasoned and skilled plumber with over 20 years of experience. Specializing in repairing and optimizing water appliances for large buildings, offices, and homes, he has a keen eye for efficiently identifying plumbing and maintenance issues. With a passion for his craft, Daniel brings extensive knowledge and expertise to every project, ensuring reliable and effective solutions for his clients.

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