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How Long Does It Take To Drain A Water Heater? [7 Amazing Unknown Factors]

How Long To Drain A Water Heater

If your water heater is having severe problems, it is obvious that you need to repair it after draining the water from the heater. But if you are confused about how much time will it take to drain the complete water, this depends on the volume of water available along with the plumbing structure of your home.

But there are also several other factors which decide the same. Here is a guide on How Long Does It Take to Drain a Water Heater which you can follow to know more!

1. Know the Gravity of Water

If the water is free-falling, the gravitational force works at 33 feet per second. The downward force thus depends on the water flow rate and the inside diameter of the pipeline. So the downward force depends on the diameter of the outline pipe as well as the type of material used in the piping.

If the surface is smooth, it will allow more volume of water to go down instantly and thus will increase the speed of draining. Apart from this, it also depends on the flow rate. It the flow rate is high, it will have higher gravitational force.

2. Check the Pressure Head

The next important factor which comes up is the pressure head. The pressure head means that it allows high-pressure water to flow through the drain pipe. According to the formula, 1 foot of elevation drop = 0.433 psi of pressure head. This means that the pressure head should have a high capacity if your heater is mounted on the top. So individually, the higher the pressure head is, the better it is for your source and outlet. 

3. Know the Pipe Material

The drain pipe factor makes it even clear on how much time will you require to clear the tank. There are two parameters for you to consider including the inside diameter and the outside diameter. It determines the volume capacity of the pipe along with the material it is built with. If the friction is high, it will naturally slow down the flow rate.

However, if it is low, the water flow rate will increase. Also if the pipe is wide in diameter, it will hold more volume but the pressure will remain low. So to make it compatible and easy, the one-inch pipe can give you both high force and individual volume to drain through the pipe. 

4. Understand the Hydraulics

The hydraulics of motion through the drainpipe involves the force and the air pressure available from the tank. While the tank is being drained, make sure that there are no airlocks to follow up. It happens mostly when the liquid is static and the air bubbles have come in.

So in such a case, the drain flow stops. So make sure that there is no airlock in the pipe to avoid any type of pressure. Apart from this, the hydraulics also affects the flow rate of the pipe to a vertical. If necessary, you need to overcome the airlock in your system.

Other Factors Affecting the Flow

Apart from these four factors, there can also be several factors that affect the time of flow. You can check them from below:

1. The first is the amount of water. If you have a small tank, it will hardly take just 1-2 minutes to drain it completely. However, if the tank is more, it may take more time.

2. Sediment Formation in the drainpipe is another factor. If there is more sediment, it will block the flow rate and thus will take the longest of minutes. 

3. Plumbing is another factor that you must keep in mind. If your heater is in the second story and most of the faucets are in the first story, it will take more time to clean up.

Frequently Asked Questions [How Long Does It Take To Drain A Water Heater?]

Q1. Why is it taking so long to drain my water heater?

A1. Sediment formation may always reduce the flow rate of water through the drain pipe. Rusts and debris do not tend to flow out of the pipe easily. So it may take more time to drain the water. In such a case, it is very important to remove the debris before the drain. 

Q2. How do you drain the water heater fast?

A2. To drain your water heater fast, try to attach a temperature-pressure release valve. This allows the water to free flow with air pressure from the top. So as the pressure increases, the water automatically drains out faster. This allows you to easily drain your water. 

Q3. How long does it take to drain a 50-gallon water heater?

A3. If you have a water heater mounted on top of the washroom, it will have high pressure while draining. Generally, the flow rate is around 10 gallons per minute. So if you have a 50 gallons tank, it will roughly take around 4-5 minutes to drain it completely. We have written a latest article on Best 50 Gallon Gas Water Heater.

Q4. How long does it take to drain a 40-gallon water heater?

A4. Most of the 40 gallons water tank comes with a high-pressure release valve. This means that the flow rate of water is very high and around 10 gallons per minute. So it will take around 4 minutes to entirely drain the water from the tank. Here is a detailed discussion.


The drain of water from the tank depends on several factors that you must keep an eye on. But if you want your heater to work properly every time you will need to maintain it. So make sure that you keep the drain pipe clean and well connected with the heater so that it does not affect the drain pipe.