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Water Heater Inlet Size [Choose The Ideal Size]

Having the right-sized water supply line is important for your heater to function properly. But among so many measurements, it’s confusing to reach out to a particular size.

What’s the right water heater inlet size?

Most of the water heater inlet size comes with ¾” or ½” diameter. ½” is a common measurement for old households. These days most water heater supply lines require ¾” diameter inlet size. For a tankless water heater, the size mostly varies from ¾ inch to 1 inch.

That was only a sneak peek of the whole issue. We’ve discussed inlet sizes in detail in our different segments. Stay with us if you want to know more.

What’s the wait for? Let’s begin!

What Is A Water Heater Inlet?

When you’re working on a water heater it’s important to know its components. For example, components like a water heater inlet. Learning about water heater inlets can give you an idea about water supply lines.

The supply line of the water heater is located at the top. It’s called a water heater inlet or cold water inlet. This pipe works as a supply line of water to the heater.

The cold water from the main water line of the house enters this inlet. The inlet then allows the water to enter the heater. After the water is heated, hot water comes out of the outlet.

Sometimes, a water softener is added before or after the pressure tank. Similarly, a water softener is installed before the water heater. This is why a working shut-off valve is added to the inlet pipe.

Why Should You Use The Right Inlet Size?

You might think that a close measurement to the right size inlet is enough. But it doesn’t work that way. You’ll need the right size inlet for your water heater to utilize it properly.

But what happens when the inlet is bigger than it’s needed? 

Using a bigger inlet is not going to get you better water flow. Instead, it might put too much pressure on your heater’s water supply. There’s no point in using a bigger pipe when other water pipes are smaller.

Similarly, using a smaller inlet will result in less water flow in the system. It will take a long time to fill the water heater. It delays the whole process. 

Using small inlet pipes can be troublesome. For a heater with a storage system, it’ll take even longer to fill the tank. That’ll make it seem as if it has a dented water heater problem.

For the tankless heater, the delay will be even more so. Tankless water heaters don’t store water beforehand. 

It works when the main faucet is open letting water enter the system. Meaning you’ll have to wait long enough until you get usable hot water. That’s why you shouldn’t use a smaller diameter inlet pipe on a tankless heater.

There are also other common issues you might face for not using the right size inlet. For example, unpleasant noises might arise from the pipe. It happens when you use smaller diameter pipes for inlets. 

Another issue is water leaking from the inlet. It happens due to the heavy pressure of the water on the pipe. The longevity of inlets will shorten for the messed-up water pressure too. You’ve to either replace the inlet or hope that the slow leak seals itself.

Choosing The Correct Water Heater Inlet Size

It’s super important to install the right size inlet for your water heater. It is to ensure sufficient water flow into the heater. Try to validate that there isn’t excessive water flow in the heater. Because you wouldn’t want your inlets to have a leaking issue so soon. 

Two types of water heaters are used for households. Let’s go through them-

Storage Tank Water Heater Inlet Size

The common size for the water heater inlet is ¾” and ½”. But ½” hoses seem to be insufficient these days. The inlet pipe must be compatible with other pipes of the heater. 

You may use flexible plastic pipes. But make sure the sizing is correct. Otherwise, the water flow wouldn’t be right.

The standard measurement is considered to be ¾” these days. In old households ½” is much more compatible. But in new households, it’s not enough. This is why people are shifting to ¾” measurements now.

Tankless Water Heater Inlet Size

Measurement for a tankless water heater is almost similar to the normal water heater. It’s directly related to the water heater’s supply line size. In the majority of cases, a tankless water heater requires a ¾” or 1” inlet pipe.

Like normal water heaters, ½” is almost an outdated size for an inlet pipe. Most tankless heaters are compatible with ¾” diameter inlets.

The required size for a water heater is always mentioned in the manufacturer’s specification. Some manufacturers permit small-diameter piping for cold water inlets.

Once you have picked the right sized inlet, you can install the water heater. But make sure you have gloves on during the installation process. 

We’ve mentioned some gloves that’ll keep your hands protected:

Product 1
Product 2

Use these if you’re installing the water heater by yourself! And that’s it!

If you are interested in buying a water heater. You can look into Rheem & Ruud water heaters.


Question: How long does a water heater last?

Answer: The water heater has a lifespan of 8-12 years if maintained with care. If you replace the parts when needed they might survive for decades even.

Question: Why does a tankless water heater go cold?

Answer: In most cases, it happens due to hot water demand outdo its capability. A dirty water filter can also be the cause. But in most scenarios chances are that the heating elements have gone bad.

Question: Should the water heater be on all the time?

Answer: No, it should be on all the time. Keep it running when you need hot water. Keeping it on the whole day will result in lots of wasted energy. It’ll also consume a lot of electricity.


That was all from us about water heater inlet size. Hopefully, you’ve gotten rid of your confusion about the inlet sizes.

See you soon in the next post!