Overview

Tankless water heaters, also known as on-demand water heaters, are becoming more popular among house owners and businesses because of their salient features like energy efficiency and space-saving design. But when buying a tankless water heater, there are a lot of technical terms and specifications to check, one of which is the gallons per minute (GPM) flow rate.

What is the GPM flow rate?

In Easy words, the GPM flow rate means the amount of water in gallons that can be heated and delivered in one minute.

In other words, it’s the maximum flow of hot water that a tankless water heater can provide in one minute.

A higher GPM flow rate means-, the water heater can supply more hot water in a small amount of time, making it suitable for larger houses for running multiple hot water appliances and fixtures at once, such as a shower, a dishwasher, and a washing machine all at the same time.

What GPM to choose while shopping for a tankless water heater

When shopping for a tankless water heater, it is important to match the GPM flow rate with your specific hot water needs. This is the important factor in tankless heaters as it doesn’t has a storage tank to store a higher quantity of water and provide them when needed as storage tank water heaters. Everything needs to be done instantly and the GPM flow rate matters according to the usage needs.

For example, if you live in a small house alone or have a small family, you may only require a GPM flow rate between 2-3, while if you are living with a bigger family with multiple bathrooms or a hot tub then you may require a higer GPM flow rate between 6-8. It’s also important to consider the inlet water temperature, as this can affect the GPM flow rate. For example, if you live in colder places where the inlet water temperature is lower, you may need a higher GPM flow rate water heater to compensate for the lower water temperature.

GPM Chart of few appliances and Fixtures

GPM Chart for appliances and fixtures

  • Sink faucet—1 GPM
  • Shower—2.5 GPM
  • Bathtub—3 GPM
  • Dishwasher—3 GPM
  • Washing Machine—3 GPM

These are general values it may vary between models and manufacturers.

Calculate the required GPM flow rate.

The GPM flow rate for your home or business to supply hot water from a tankless water heater can be calculated by adding the appliances or fixtures where you want to get hot water simultaneously.

Let’s take an example considering the above GPM chart. A house has 1 sink faucet, 1 shower, 1 bathtub, and 1 washing machine. We should not all their GPM values together, first we have to choose the appliances or fixtures which we want hot supply simultaneously and then add their GPM.

  • If we want hot water in the sink faucet, shower, and washing machine simultaneously, GPM would be 1+2.5+3 =5.5(6approx).
  • If we want in a sink faucet, bathtub, dishwasher, and washing machine then it would be 1+3+3+3=10GPM.

Inlet water temperature

It is also crucial to consider the inlet water temperature when determining the appropriate GPM flow rate for a tankless water heater. The inlet water temperature refers to the temperature of the water entering the unit before it is heated. In colder climates, the inlet water temperature may be lower, which can affect the GPM flow rate. The lower the inlet water temperature, the more energy and time it takes to heat the water to the desired temperature, you may need a higher GPM flow rate to compensate for the lower water temperatures.

For example, if you live in a climate where the inlet water temperature is around 40 degrees Fahrenheit and requires a 3 GPM flow rate, a tankless water heater with a GPM flow rate of 3 may not be sufficient to provide hot water to multiple fixtures or appliances simultaneously. In this case, you may require a higher GPM flow rate of 4 or 5 to compensate for the lower inlet water temperature.

calculating temperture rise of tankless water heater formula

You need to calculate the temperature rise, which can be done by subtracting the inlet water temperature from the required hot water temperature. If the temperature rise is 60-70, you need to look for a heater which can provide 3 GPM hot water with a temperature rise of 60-70. Look for the model specifications to find the information on temperature rise.

On the other hand, if you live in a climate where the inlet water temperature is around 60 degrees Fahrenheit, a GPM flow rate of 3 may be sufficient to provide hot water to multiple fixtures or appliances simultaneously.

Also read: Do tankless Water Heaters need an Expansion Tank?

Conclusion

In summary, when purchasing a tankless water heater, it is important to match the GPM flow rate with your specific hot water needs, taking into account the size of your household, the number of hot water appliances, and the inlet water temperature. By doing so, you can ensure that your tankless water heater can meet your hot water demands and provide efficient and cost-effective hot water for your home. And remember, don’t be afraid to ask questions or do your research, and you’ll be able to make the best decision for your home and your family.

If you have any questions or concerns, don’t hesitate to leave a comment below! Our team is here to assist you and provide all the information you need. Your feedback is important to us, so please feel free to share your thoughts and we’ll respond as soon as possible.

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