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What is GPM?

GPM stands for Gallons Per Minute, and it is a crucial metric when considering tankless water heaters. GPM measures the flow rate of water that the heater can provide at a given temperature rise. Essentially, it tells you how much hot water the unit can produce in a minute, which is vital for understanding whether a particular model can meet the hot water needs of your household.

Why GPM is Important:

  1. Determines Capacity: The GPM rating helps determine the capacity of the water heater, indicating how many hot water applications (like showers, washing machines, and sinks) can be used simultaneously without running out of hot water.
  2. Sizing Your Water Heater: Properly sizing a tankless water heater to your home’s needs involves calculating the total GPM required at peak usage times. This ensures that the water heater you choose can handle the demand when multiple fixtures are in use at the same time.
  3. Efficiency and Comfort: A water heater with a GPM rating that matches your household’s demands ensures efficient operation and continuous comfort, providing a steady supply of hot water without unnecessary energy use.

Calculating Your Needs:

To calculate your needs, you’ll need to add up the GPM of all fixtures that could potentially be in use simultaneously. Here’s an example:

  • Shower: 2.0-2.5 GPM
  • Kitchen Sink: 1.0-1.5 GPM
  • Dishwasher: 1.0-1.5 GPM
  • Washing Machine: 1.5-3.0 GPM

If all these could be in use at the same time, you would need a tankless water heater that can provide somewhere between 5.5 to 8.5 GPM to ensure you don’t run out of hot water.

Consider Temperature Rise:

The actual GPM output of a tankless water heater can also depend on the temperature rise required, which is the difference between the incoming cold water temperature and the desired hot water temperature. A unit may produce a higher GPM of hot water in a warm climate where the incoming water temperature is higher compared to a cold climate where the water heater needs to work harder to heat the water to the desired temperature.

Choosing the Right Unit:

When selecting a tankless water heater, consider both the GPM rating and the temperature rise at that flow rate to ensure it meets your hot water needs in the most energy-efficient manner. This approach will help you choose a unit that not only saves energy but also provides the convenience and comfort of continuous hot water.

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