Choosing the Right Size of a Tankless Water Heater

While there are benefits that come with using a tankless water heater, the size still does matter. Sure, you can take advantage of its consistent water supply, longevity, easy installation, energy reduction, and temperature control. However, the size of your tankless water heater can impact its overall efficiency and water demand. 

That’s why it’s important to factor in the size of the tankless water heater for your household needs. Below are two key factors to consider when looking for the right size of your water heater.


Flow rate

In a nutshell, the flow rate is expressed in gallons per minute (GPM). It refers to how much hot water your tankless unit will be able to supply. As far as the flow rate is concerned, here’s what you need to consider:

  • Showerhead – 2.5 GPM
  • Bathroom sink faucet – 1.0 GPM
  • Tub faucet – 4.0 GPM
  • Washing machine – 2.0 GPM
  • Kitchen faucet – 1.5 GPM
  • Dishwasher – 1.5 GPM

Given these, determine the number of hot water fixtures your household uses during peak hours. From there, you’ll be able to assess the flow rate your home requires. Depending on the size you install, a tankless water heater usually restricts your family to one or two hot water activities at a time. 

Overall, you want to install the unit that can provide enough flow rate to meet your household needs.


Temperature rise

Apart from the flow rate, you also have to factor in the temperature rise in a tankless water heater. It refers to the temperature of the water when it goes in and when it comes out. 

For instance, the temperature you need ranges from 102 degrees for the bathtub and shower to 120 degrees for the dishwasher and washing machine. From here, check the specifications of the tankless water heater and see if the unit can meet these requirements.

Ultimately, you have to know the average groundwater temperature in your region and see what particular size of a tankless water heater can best meet your needs.


Incorporating the two factors

At this juncture, you have to put the two crucial factors into utmost consideration—flow rate and temperature rise. They both go hand in hand when it comes to your selection of a tankless water heater. 

There’s no need to worry, though, as the size of the tankless water heater is indicated as a combination of flow rate and temperature rise. 

Therefore, you crunch the numbers and see what particular tankless water heater will best serve your household requirements.



Overall, size does matter when it comes to tankless water heaters. While a small unit may not be able to meet your water supply, an oversized one can affect energy efficiency. 

That said, consider the two factors that go into sizing a tankless unit, so you know what to install in your home. Ultimately, the tankless water heater size must be just right to meet your expectations.

Our professional plumbers are highly trained and skilled in plumbing installations and repairs. If you’re looking for water heater installation services in San Diego, get in touch with us today to see how we can help!