How Do I Know the Right Size of a Tankless Water Heater? · Rainforest Plumbing and Air

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How Do I Know the Right Size of a Tankless Water Heater?

Posted by Ryan Forest

Thinking of upgrading to a tankless water heater? It is a smart decision, especially if you are looking to improve your home’s energy efficiency. But you need to make sure you are installing the right size, which comes down to two calculations.

Too small of a water heater will lack producing enough water, where an oversized water heater will produce too much water, making it a waste and defeating the purpose of a tankless water heater, which is overall energy efficiency. 

Your tankless water heater needs to be the right size to meet the needed expectations. Our reliable plumbers in the east valley can come out and help you determine the correct size!

Look at the Flow Rate

The flow rate of a tankless water heater is exactly how much water it can produce. This is measured in gpms – gallons per minute. You need to ensure that you are getting a water heater that has a high enough flow rate for your needs.  

Below is the typical flow rate of fixtures around your house:

Bathroom Sink – 1.0gpm

Showerhead – 2.5gpm

Bathtub Faucet – 4.0gpm

Kitchen Faucet – 1.5gpm

Dishwasher – 1.5gpm

Washing Machine – 2.0gpm

So, what exactly does this mean? Well, if you plan on two people taking a shower in the morning at the same time, while also running the dishwasher, you are looking at a tankless water heater with a flow rate of at least 7gpm. 

Look at the Temperature Rise

The temperature rise of a water heater is figured out by taking the temperature of the water when it enters the water heater and subtracting it by the temperature it needs to be when exiting the hot water heater.

This sounds complicated, but it really isn’t. You just need to know the average temperature of the groundwater in your area. Our plumbers can help you answer this. But the groundwater tends to be pretty warm in places like Arizona. 

Let’s look at an example…

On the east coast, the groundwater tends to be around 52 degrees. So, that means the water is 52 degrees when entering the water heater. We want the water to be warmed to around 102 degrees when taking a shower, but up to 120 degrees when running your dishwasher. That means that the temperature rise of the water heater needs to be between 50 to 70 degrees. 

In Arizona, we are looking at a temperature rise of only about 30 degrees.  

Installing the Right Tankless Water Heater

When it comes time to picking out a tankless water heater, you will look at these calculations. For example, a tankless water heater that only needs a temperature rise of 30 percent can have a flow rate of 8.0gpm.  

We always recommended scheduling an appointment with Rainforest Plumbing and Air before you make any final decisions. Our plumbers will come and access the area, helping you find the right tankless water heater for your home.