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Water Heater Supply Line Size: Choose The Perfect Size

Supply lines with incorrect sizes take a long time to fill the tank. As a result, hot water comes late. So, if we know the specific supply line size to use, it can save us time. 

What is the ideal water heater supply line size?

¾ inch diameter and 16-24 inch length supply lines are ideal for water heaters.  And, it has some advantages that make it more user-friendly. Although people also use ½ inch diameter supply lines in the older water heaters.

These are all you need to know about supply line size in short. However, if you want to know more, spare a few minutes and read along.

So let’s dive into the details!

Factors to Consider When Choosing The Right Water Heater Supply Line Size

There are some drastic changes when it comes to comparing these supply lines. These two supply lines work for the same purpose. Now, after reading the comparison, you’ll be able to choose what is best for you.              


The cost varies considering the quality and the total length of the supply line. 

For a good quality ¾ inch supply line, it costs around 6-50 dollars. Copper supply lines are the best for use. The standard length of the water supply line is 24-32 inches. This will cost around 10-30 dollars. 

½ inches diameter supply lines are much cheaper than a ¾ water supply line. Quality ½ supply line costs around 20 dollars. The standard length of the water supply line is 12-16 inches. So, a good quality ½ inch 12-16 supply line will cost 8-15 dollars. 

Water Pressure

Water pressure is a vital thing to discuss when using a water heater. A ¾ inch water supply line fills a 55-gallon heater just in a minute or two. But, a ½ inch supply line fills that heater in 25 minutes. 

As you see, ¾ inch supply line flow rate is 20 GPM. So, when you’re running the heater you want to fill the gallon quickly. A ¾ inch water supply line ensures the correct flow rate in a heater. 

In case you’re looking for the best quality ¾ inch water supply line, we have some suggestions for you:

Product 1 
Product 2 

Now you have your supply line, go with the flow! 

The length also depends on whether you’ve installed a water heater on its side or vertically. If it is installed vertically, you need a smaller supply line.

If it is installed horizontally, you need a longer pipe. The reason is the distance between the supply line and faucet increases at that time. 


Copper supply lines are the most durable supply lines. A copper supply line hardly leaks and can take the pressure of water. So, both ½ and ¾ stainless copper water supply lines last for more than 20 years. 

If you’re using pex water supply lines, it can’t take the full pressure of water. Temperature is also a fact here. A pex water supply line can’t handle boiling temperature water, it cracks. It might also cause brown water to drain after installing the supply line.

If you’re using the ¾ supply line, it can take all the water pressure. It can also run boiling water through it. The length of the supply line plays a vital part in this case. The 2-meter line flows water quickly that’s why the pressure stays normal most of the time.     

The ideal size of a supply line is a 2-meter ¾ inch supply line.  

What Should The Standard Size Of Water Heater Supply Line Be?

¾ inches diameter is considered the ideal size of water heater supply lines. People used ½  inches diameter supply lines in the heater in the 90s. But the problem with the ½  inches supply line was that the water pressure was low. 

If you want to install a supply line in the heater for showers, install a ¾ inch supply line.

Correct sizing is important because it ensures the proper flow rate. But be careful about leaking the heater. ¾ water heater sometimes malfunctions and starts leaking. There are many other reasons for a water heater leaking as well. 

A ¾ inch supply line is preferred for multiple showerheads, body sprayers, etc. This supply line ensures the proper pressure of water even when all the heads are turned on. These days, ⅜ inch supply lines are also popular. ⅜ inch pipes are longer compared to ¾ inch supply lines.   

Some people experienced bad performance when they installed a ½ inch supply line. That’s why you must keep in mind that your supply line size is optimal.

What Happens When Supply Line Size Is Smaller Or Bigger?

Suppose you have a 55-gallon water heater and you installed a ½ diameter supply line. It will take at least 25 minutes to fill it up. 

A longer length of the supply lines also affects the flow rate. It takes more time to pass the water as it has a long length. For example, a ½ inch 2 meter supply line takes more than 30 minutes to fill a 55-gallon water heater. 

If you install a ¾ inch 2 meter supply line, it will take at least 5 minutes to fill the heater. But if you install a ¾ inch 1 meter supply line, it will take 2-3 minutes to do the job. Now, if you use a half-meter supply line, it can’t take the pressure of the water. 

The ideal size of a supply line is a ¾ inch 1-meter length. It will ensure hot water will come in 3 minutes. The longer you wait the longer you will waste time. You don’t want it, do you? Before installing a supply line, it’s also important to know the size of a water heater. The Inlet allows cold water to come through the supply line. So, make sure the inlet size matches the supply line.  

That’s why installing the right size of the supply line is very important.


Question: Why Are Pex Supply Lines Bad?

Answer: Pex supply lines are way more complicated to use. For example- they don’t work well with chlorine and UV rays either. Pex supply lines are also bad for their water pressure capability. Too much water pressure can crack the pex line. 

Question: Are PVC pipes good for water supply?

Answer: Yes, PVC pipes are affordable and durable pipes for water supply. Although they are not very well compatible with high temperatures. But, you can use PVC-Hi to do the job. It is flexible, cost-efficient, and durable. 

Question: How much does it cost to replace a water heater supply line?

Answer: It costs around 120-150 dollars to replace a water heater supply line. But with the proper tools and guidelines, you can do it yourself. This will save you at least 70-100 dollars. So it is wise to fix it on your own. 


That’s all for today! Now you know the ideal water heater supply line size. A ¾ inches diameter supply line is the best option for using a water heater. It ensures the water flow rate and fills the gallon quickly. 

We hope we have helped you with this article. Till then, good luck!