How Long Does It Take To Fill a Water Heater?

The water heater is one of those items that most homeowners have little idea about until it breaks down.

A hot shower is a luxury that many people take for granted, but even though the concept of a water heater is rather simple, it may still be difficult to grasp.

When it comes to filling a water heater, how long does it take? This is a question that many homeowners have daily.

The following blog article will provide you with helpful information on how long it takes to fill a water heater and some of the most typical difficulties that might cause your tank’s water to heat up slowly.

What Is the Process of Filling a Water Heater?

As your plumbing fixtures and water appliances take hot water from the water heater, the water level lowers. It fills the hot water tank with cold water and then restarts the heating process.

How Can I Tell If My Water Tank Is Full?

When you turn on the water pressure valve, no more residual air comes out, which indicates that the hot water tank is full.

Certain systems now incorporate a function that displays the tank’s water level.

Factors That Influence the Amount of Time

It’s best to think about the following possible reasons to answer this question:

The Size of Your Tank:

It all depends on the situation. A family of two may be unhappy with their 30-gallon tank, whilst a family of five may be able to live happily with one.

The size of the tank is solely determined by how you use your water. If you use more than three water appliances in the same hour, you will most certainly want a huge tank.

However, if you never use more than one hot water appliance in the same hour, a smaller tank will suffice.

Regardless of this, be sure the tank capacity is appropriate for your needs before purchasing a new water heater.

Feel free to check out this article to help figure out what size is suitable for your needs.

The Age of the Tank:

Standard tank water heaters have an average lifespan of 8 to 12 years. However, if you take great care of it, it might live for more than 15 years.

An anode rod is included in the tank, which draws corrosive substances into the water. This helps to keep the internal lining of the tank from corroding.

The rod becomes worn out after 10 years of usage and no longer performs properly. As a result, corrosive particles settle on the tank’s internal lining.

Some settle to the bottom of the tank and eventually damage it. The tank may begin to leak at this stage.

Check out this post to learn the easiest way to deal with leaks.

Tankless water heaters are more modern than tank water heaters, which means they have a longer lifespan. There are two main types which include:

  • Tankless Electric Heater
  • Tankless Gas Heater

One of these may normally last you 20 years. You might be able to stretch it to 30 years if you maintain it properly.

Because of its capacity to heat water just when you need it, it’s also known as an “on-demand water heater.” They don’t have to run all the time to keep the water hot, therefore they last longer.

Corrosive elements corrode them as well, albeit at a far slower rate.

Now that you know how long each type of water heater is expected to last, you can estimate when you’ll need to replace it.

If you forget when you got it, you may also check the serial number. This might help you keep track of how long you’ve had it, which is especially useful if you buy a used electric model.

For a closer look into how long water heaters should last check out this post.

The Size of the Supply Line:

It will take a long time for your tank to fill if your water supply line is the wrong size.

This implies there will be a lengthier wait for hot water. As a result, knowing the particular supply line size you should use for your system will save you a lot of time and effort.

3/4 inch diameter and 16-24 inch length are suitable to supply lines for water heaters. This size is also more user-friendly.

In an old water heater, you will have supply lines that are 1/2 inch in diameter. Assume you have a 1/2-inch supply pipe installed on your 55-gallon water heater.

Filling it up with a steady flow of water would take at least 25 minutes.

The water flow rate is also affected by the length of the supply line. The longer the pipes are, the longer it takes for the water to move through them.

In comparison to the one above, filling a 55-gallon water heater with a 1/2 inch 2-meter supply line takes more than 30 minutes.

If you use a 3/4 inch 2-meter supply line, it will take at least 5 minutes to fill your heater. Installing a 3/4 inch 1-meter supply line, on the other hand, will reduce the time to 2-3 minutes.

A supply line with a length of 3/4 inch and a diameter of 1 meter is recommended.

This ensures that hot water will be provided in under three minutes. Before you install a supply line, you should think about the size of your water heater.

Because the intake allows cold water to enter through your supply line, it must match.

This is why experts urge you to choose one with caution.

How Cold Outside Temperature Is:

The effects of cold weather on water heaters are undeniable! When it’s chilly outdoors, the air temperature drops, but the temperature underground drops as well.

Any water entering your water heater is quickly cooled by the very low incoming temperature.

As a result, your electric water heater will have to work extra to get the ever-cooling water up to higher temperatures.

When temperatures drop to dangerously low levels, pipelines have the potential of freezing as well. If this happens, your pipes may over-expand and begin to leak, or even worse, burst open!

While your tank water heater is heating the water inside, cold incoming water comes via the intake, cooling the water down again. It’s a vicious cycle that’s exacerbated if your water heater is outdated.

A water heater that is more than 8 years old, for example, may struggle even more to maintain the temperature warm throughout the winter.


Water heaters are usually pre-set at 140 degrees. For two reasons, many manufacturers recommend setting the thermostat at 120 degrees.

The first is to prevent scorching, which protects toddlers and newborns. The second is to reduce energy use.

In the winter, 120 degrees may not be enough to make your water hot enough. It might be a good idea to raise the temperature setting by 5 to 10 degrees and see if the water temperature improves.

Before messing with the settings, you should first review the instructions that came with the water heater.

You should be able to predict how long it will take to fill the tank once you’ve examined these elements.

How Long Does It Take for a 40-Gallon Tank to Heat Up?

The time it takes for a water heater to heat back up once the tank has been depleted is influenced by a number of factors.

The temperature of the water injected into the device, as well as the type of heating element included in the hot water heater, are among these factors.

We need to look at two distinct ratings to determine a water heater’s efficiency: first-hour and recovery ratings.

Both of these are beneficial since they influence the time it takes for the water to heat up.

A sticker for your energy guide should be slapped onto the side of your water heater, and it should display both ratings. Maintaining your unit on a regular basis will also help it run at its best.

Draw Efficiency

The drawing efficiency of both gas and electric heaters is calculated using a formula that accounts for 70% of the tank’s total storage tank capacity.

The drawing efficiency of a 40-gallon water heater is 28 gallons. For most people, 40-gallon tanks are on the small side, but they are a wonderful tank size.

This indicates that when the hot water is being drained, the cold water is being drained at the same time.

A 50-gallon tank, on the other hand, has a draw efficiency of 35 gallons.

Tanks with a capacity of 50 gallons are ideal for houses with three bathrooms or two bathrooms and a washing machine.

A one-person bath uses around 10 gallons, a washing machine uses approximately 20 gallons, and a dishwasher uses approximately 10 gallons of water.

First-Hour Rating

The amount of water drawn from a water heater in one hour is directly proportional to its first-hour rating.

With the device set to a water temperature of 135 degrees, this quantity is in gallons per hour.

This rating is based on each unit’s performance in tests set by the US Department of Energy. On a sticker, the results of the energy efficiency tests are presented.

During the test, three gallons of hot water are drawn every minute for the length of the test, which stops when the water cools to a temperature of 25 degrees.

When the temperatures rise to 135 degrees, the procedure continues for another hour without interruption.

The amount of water drawn during this hour represents the full hourly capacity (FHR) of the water heater, which indicates how much water will be available at peak demand periods throughout the day.

Water Heater’s Recovery Rate

The quantity of power that a unit gets determines its recovery rating.

This rating helps you determine the recovery time of the heater.

Gas water heaters are more energy-efficient than electric water heaters, and they heat water in half the time.

The temperature of the water entering the device and the thermostat setting used to heat the water determine the heating time of a 50-gallon water heater.

The power supply is clearly in control of both of these.


To summarize, the length of time it takes for your heater to fill up is dependent on many factors.

However, now that you’ve read the above, you are better equipped to figure out how to make sure you get lots of hot water.

If you have any questions, please post them in the comments section below. We are always willing to help!

by Richard Kelly

Having experienced significant success as a house flipper, I am often approached with questions about all things home improvement. That’s why I decided to start this site. My objective is to share all of the insights I have accumulated over the years so other people can design the homes of their dreams.