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How Long Does It Take to Drain a Water Heater? – Average Time

Fact checked by Stephen Conklin

how long does it take to drain a water heater

Are you a first-time owner wondering how long does it take to drain a water heater? Draining or flushing a water heater is an essential procedure for maintaining the appliance’s functional integrity. Draining the water helps you clean the tank’s interior, removing accumulated sediments and debris.

The time needed to drain a water heater depends on a few factors. Join me as we examine those factors to determine how long it will take you to drain your water heater.

Table of Contents

Drain a Water Heater – How Long Does It Take?


Draining a water heater can take anywhere between five and fifteen minutes, depending on the following factors.

1. Tank Capacity

In general, the larger the tank capacity, the longer it takes to drain the water heater. For example, suppose you have a 40-gallon water heater and a 60-gallon unit. In that case, you can expect the 40-gallon appliance to drain faster than the other product, all other factors being equal.

2. Drain Valve Size

All tank water heater systems have a drain valve at the tank’s bottom for emptying and flushing. It is also a crucial factor in determining how long it takes to drain a water heater. In the case without a drain valve, I recommend you to read these guides for the best implementation.

Like tank capacity, a large-diameter drain valve will drain more water per unit of time. For example, a 1-inch-diameter drain valve will empty more water per second than a ½-inch or ¾-inch port can.

Going back to our example, suppose the 40-gallon water heater comes with a ½-inch drain port, and the 60-gallon unit has a 1.5-inch drain valve. In that case, the 60-gallon water heater will drain slightly faster than the 40-gallon unit.

3. Water Pressure

A hose with a 10 GPM flow rate will push the water faster through the drain port than a hose with a 7 GPM flow rate. Of course, this is only true if both water heaters have the same drain valve size and tank capacity.

In general, water heaters drain nine gallons per minute (GPM) to 17 GPM. If you have an 80-gallon water heater, you can expect it to drain in five to nine minutes.

It is essential to understand these numbers only reflect the actual draining of the water from the tank. It does not include preparation time and other related activities. You can drain a hot water heater quickly by preparing all the materials and tools beforehand and observing a systematic process of draining.

How Long Does a Water Heater Take to Flush

Flushing a water heater is different from draining it. First, you can flush your water heater anytime you feel like the water is going stale. On the other hand, draining the water heater is only advisable every six to twelve months.

Second, draining the water heater requires you to shut off the cold water supply line, allowing you to empty the tank contents. On the other hand, flushing needs the water supply line to be open while also leaving the drain port open.

The cold water inflow pushes stale water through the drain port, allowing you to replenish it with fresh water. The downside of this approach is that you cannot evaluate your water heater tank’s interior because it is constantly full of water.

So, how long does it take to flush a water heater? Everything depends on your preferences. Some people like to get a water sample and test it for impurities, while others only perform a visual inspection. If they think the water is already good for them, they can stop the flushing.

Hence, flushing a water heater can take anywhere between 15 and 45 minutes.

How Much Time Do You Need to Drain a 40-gallon Water Heater


If you are wondering how many minutes will a 40 gallon water heater take to drain, the answer lies in its drain port diameter and water pressure.

It would be wise to remember that the greater the water pressure, the faster the water comes out through the drain valve. However, you must also consider the drain port’s diameter. You can empty the water heater a lot faster with a larger opening than a small one.

Hence, it can take you three to five minutes to drain a 40 gallon water heater, depending on the water pressure and drain port size. Remember, this period does not include preparing the water heater for draining and wrapping up the process.

How Much Time Do You Need to Drain a 50-gallon Water Heater

Using our 9-17 GPM average drain rate, you can expect to drain a 50 gallon hot water heater within three to six minutes.

Again, it does not reflect other activities related to emptying the water heater. That is why it is not unusual to complete the whole process in 15 to 45 minutes, depending on how fast you work and the availability of materials or tools needed.

I recommend preparing your work area and the materials beforehand to shorten the overall water heater drainage process.

Why Drain a Water Heater

Conventional water heaters come with storage tanks. Cold water enters the tank, and a device heats the water to the ideal temperature before letting the water out of the tank and into the different faucets, water appliances, and other water fixtures.

According to the US Geological Survey, water is never clear. It always contains sediments, suspended solids, and other substances. Although most of the water coming to our homes undergo treatment at a water treatment facility, the procedure does not purify the water.

Hence, there will always be substances denser than water. These dense particles settle at the tank’s bottom and sides, accumulating over time. Not only do these compounds affect water quality, but they can also impact the water heater’s performance.

For example, high calcium carbonate levels in the water can lead to scale formation. It can harden and impact the water heater’s heating efficiency, extending the heating time or lowering the water temperature.

That is why it is essential to drain the water heater tank regularly. Emptying the tank allows you to scrub the interior and remove surface contaminants. You can then spray it with water to ensure complete cleaning.

How Frequently Should I Drain a Water Heater

As mentioned, sediments accumulate at the tank’s bottom over time. You can drain your water heater every ten to twelve months if you have a water softener, sediment filter, or a water filtration system.

Water softeners work by dislodging calcium carbonates from the water. These compounds and other hard minerals can clump together and stick to the inside walls of plumbing systems, including your water heater. Removing hard minerals prevents scale formation at the water heater tank’s bottom.

On the other hand, a sediment filter only removes particles larger than the device’s pore size. For example, a 5-micron filter can only eliminate substances larger than 5 microns. Smaller particles can still pass through the filter and deposit at the tank’s bottom.

If you do not have any of these water treatment systems, it would be best to drain your water heater every six to eight months. You might also want to drain it more frequently if you have hard water.


Answering the question, how long does it take to drain a water heater, requires an understanding of a few factors. Tank size, drain port diameter, and water pressure can impact how fast you can drain a water heater. In general, the actual tank emptying should not last more than fifteen minutes, although other activities can extend the whole process to 45 minutes.

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