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Serving The Greater Fresno Area Since 1970

Serving The Greater Fresno Area Since 1970


Donald P. Dick Air Conditioning Blog

How Do You Determine What Size Your Tankless Water Heater Should Be?

How Do You Determine What Size Your Tankless Water Heater Should Be?Sizing a tankless water heater may look tricky at first, but there are a few steps to finding the right one for your home and situation. The correct water heater, whether conventional storage tank or tankless, will ensure that you have hot water when and where you need it. Tankless water heaters are rated by temperature rise and flow rate, in other words, how hot the water gets and how much is used at once. You need a water heater that heats enough water hot enough for each device that’s expected to be used concurrently. Consider the following:

  1. How many places will you be running hot water at once? Do you have multiple showers running in the morning? Find the flow rate for each device you’d be running hot water through simultaneously, and that’s your flow rate. So if you have two shower heads with a flow rate of 2.2 gallons per minute, and  you want to run a bathroom faucet and kitchen faucet at the same time as well, and each of them are at 2.2 GPM, your flow rate would be 8.8 GPM. In this particular case, that might be too much for one tankless water heater, so you’d need to either bring in a second or reduce the flow rate of your faucets.
  2. How cool is the water that needs to be heated and how hot does it need to be? The difference between the two is temperature rise. Assuming your incoming water is about 60 degrees and you want to heat it to 120 degrees, your temperature rise would be 60 degrees.
  3. You can heat less water hotter. If you have a tankless water heater rated at 40 degrees temperature rise and 2.0 GPM, that same water heater can get a temperature rise of 80 degrees at a reduced flow of 1.0 GPM.

Tankless water heaters are a compact and efficient way to provide on-demand water heating. To get the most out of these systems, pick a water heater that matches your temperature and volume needs. Want more expert advice about tankless water heaters or other home comfort issues? Please contact us at Donald P. Dick Air Conditioning, serving the Fresno area for over 40 years.

Our goal is to help educate our customers in the greater Fresno, California area about energy and home comfort issues (specific to HVAC systems).  For more information about tankless water heaters and other HVAC topics, download our free Home Comfort Resource guide.

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