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

Fact checked by Stephen Conklin

how long does it take a water heater to heat up

Is this your first time using a water heater that you find yourself asking, how long does it take a water heater to heat up? We have been in your shoes before, and we completely understand why you would like to know how fast your water heater reaches its ideal temperature.

While hot water heaters provide you with hot showers and hot water for your coffee or tea, they are not magical devices. These products still require time, 30 to 80 minutes on average to warm the water before you get to enjoy a shower or drink.

The good news is that knowledge of water heat-up times can help you plan your hot water-related activities. Let us learn more.

Table of Contents

Initial Heating Times

Many first-time owners wonder how long it often takes for a water heater to heat up for the first time. Unfortunately, there are no concrete answers because there are many factors affecting water heater warm-up times.

In general, water heaters with tanks take longer to heat than tankless water heaters. Moreover, a gas heater heats faster than an electric model. Hence, you can expect a tankless electric water heater to give you warm water faster than a gas water heater with a tank.

It usually takes 30 to 40 minutes for a gas hot water heater to heat up after installation. On the other hand, an electric water heater will require about an hour to 80 minutes.

Tank systems take a while to elevate the water temperature owing to their design. The incoming water temperature is a primary concern. As the tank water heater accepts the incoming water, heating elements slowly warm the surrounding water until all the water in the tank is at its ideal temperature.

On the other hand, tankless systems warm up almost instantaneously. As the water passes through coils in the device, it picks up the warmth from a heating element. It does not take long before you can enjoy hot water from a tankless water heater.

These devices provide an endless supply of hot water, allowing you to enjoy all the hot water you need. After all, you can never have too much hot water. You can also speed up the heating process by using two heating elements.

How Long Does It Take for a Water Heater (Tank System) to Heat Water?


Tank heaters store water for different purposes. A gas tank water heater takes about 30 to 40 minutes to warm up, depending on the gas tank size and the heater’s BTU (British Thermal Unit) rating.

The BTU of a gas heater refers to the amount of heat it produces to add one degree Fahrenheit to a pound of water. You can convert gallons to pounds by multiplying the gallon value by 8.329 pounds.

Suppose you have a 50-gallon gas heater tank. You can determine its capacity in pounds by multiplying 50 gallons by 8.329 pounds to get 416.45 or 415 pounds.

If you want to determine heat-up times, the process is complex. We can say that a water heater with a higher BTU rating (i.e., 100,000 BTU) will warm the water faster than a device with a low BTU rating (i.e., 50,000 BTU).

If you have a 40-gallon tank with a 40,000-BTU gas water heater, you can expect to heat the water in thirty minutes at a rate of 30 seconds per gallon. You can also shorten the waiting time if you double the amount of BTU.

You must understand that this estimate presupposes you are starting with a cold tank. If the tank still has water, the warm-up time is shorter, depending on the volume of cold water entering the tank.

In general, gas units and gas counterparts can give you shower-perfect water in half an hour.

Heat-up Time of Electric Water Heating Systems

Are you wondering, how long does an electric hot water tank take to heat up? Would it surprise you to learn that a tankless electric water heater takes 60 to 80 minutes to reach your desired temperature?

Electric water heaters have a similar design to gas-powered units, except for the heating element. Whereas gas water heaters rely on gas to produce heat, electric water heaters run electricity through a rod. Agitating the electrons produces heat, raising the water temperature.

Unfortunately, electron agitation-based heat production is slower than fire-generated heat. The burner’s location at the tank bottom also promotes improved heat dissipation – it moves naturally upward.

On the other hand, an electric heating element is on the tank’s side. Heat does not travel far from the heating element to the other side of the tank because it naturally rises.

That is why it takes a longer time for an electric water heater to heat water. It is also the reason why many electric units come with a smaller tank capacity than gas water heaters.

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


Gas tankless water heaters are perfect if you are tired of writing hot water to come back after your kids spend several hours in the shower. These appliances do not have tanks to store and heat water, working by a different mechanism.

People also call these systems on-demand water heating systems because they only heat the water when you need warm water. You do not need to water for the water heater to heat the water, allowing you to expect warm water instantly.

Incoming water enters the water heater and runs through a series of coils. In the case of a gas-powered tankless system, the burner heats the coils, ensuring you have the ideal water temperature when you turn on the showerhead or faucet.

Hence, it should not take more than a few seconds for the water to warm up. People can expect hot water immediately.

Heat-up Time of Tankless Electric Systems

A tankless water heater takes a few seconds to reach its ideal temperature. The heat-up time of a tankless electric hot water heater is almost similar to a gas-powered system. I say ‘almost’ because the gas burner produces more intense heat than metallic heating elements.

The heating element wraps around the coils inside the water heater, raising the water temperature as they move along the pipes.

While an electric tankless water heater is an on-demand system, it delivers lukewarm water with simultaneous water use. For example, five people using warm water simultaneously can reduce the water temperature over time.

What Factors Affect the Heating Speed of a Water Heater?

You know that a water heater’s heat-up time hinges on a few factors. Your understanding of these variables can help you explain why one water heater heats up faster than another.

  • Water Heater Size

Not all water heaters have the same capacity. Larger tanks provide you with more warm water with an average gas water heater capable of holding about 40 to 50 gallons.

Heater tank capacity can also impact the water heater’s first-hour rating and recovery time. The first-hour rating reflects how many gallons of warm water the device can produce per hour after a full tank.

On the other hand, the recovery time reflects the system’s ability to deliver warm water in one hour after emptying its contents. Heating efficiency and tank size are crucial factors affecting recovery time. Incoming temperature can also impact the recovery time.

  • Temperature Rise

Temperature rise is the difference in temperature between the incoming water temperature and the water output.

For example, you can expect a groundwater temperature of 60 degrees Fahrenheit if you live in cold regions. It can be an ice-cold shower in these areas. Compare this with sunny Florida, and you can get a water temperature of about 80 degrees Fahrenheit.

For most people, the most comfortable water temperature to shower with is between 100 and 105 degrees Fahrenheit.

What you must realize here is that the lower the inlet water temperature, the longer it takes for it to heat. For example, 60-degree Fahrenheit water will take a longer time to reach 100 degrees than 70 or 80-degree Fahrenheit water. The higher the temperature rises, the longer it is to heat water.

  • Fuel Type

Did you notice from the preceding sections that gas water heaters heat water faster than an electric version? While electricity and fire produce heat, they have different ways of doing it.

Fire reflects the interplay between heat, fuel, and oxygen, making it a chemical process. The resulting combustion breaks chemical bonds, which releases thermal energy we know as heat. Hence, gas heat is hotter than electric.

On the other hand, electricity is nothing more than the movement of electrons through a conductor. Some of these electrons bump into other electrons or other atomic particles, resulting in friction and heat.

Some households use a solar heater with sunlight as a backup energy source. While using a solar heater to heat the water is cost-effective, the waiting time can be greater than heating water through gas burners or electric elements.

  • Maintenance Issues

Failing to clean the water tank regularly can lead to sediment buildup and limescale formation at the heating elements. There can be dissolved minerals, too. The combination of mineral deposits and sediment buildup can affect the system’s heating abilities.

The issue is more pronounced in households with hard water because of the increased calcium, iron, and other heavy metals in the water, leading to more stubborn sediment buildup. These molecules can form rust or limescale, undermining the plumbing and water heater’s integrity and functionality. A water heater for hard water is a perfect choice; click here to learn more about the top-rated water heaters for hard water.

  • Pipe Diameter

We all love using large-diameter water pipes because they bring more water to the shower, kitchen sink, and other areas of the home. These pipes also have a higher flow rate, equivalent to more hot water for everyone.

Unfortunately, the increased water volume can also translate to longer heat-up times for the water heater.

  • Distance to Water Appliance

A water heater located 100 feet from the shower will have a slightly lower water temperature at the shower end than a device 50 feet away. That is why water heater installers check the device’s distance to all hot water-using appliances to maximize the warm water.


How long does it take a water heater to heat up? A water heater’s heat-up time depends on the water heater type (tank vs. tankless), heat source (gas vs. electric), tank capacity, distance to appliances, tube diameter, and current condition of the plumbing and water heater.

You can expect to have warm water almost instantly with tankless systems, while tank units will provide you with warm water within 30 to 80 minutes.

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