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Sizing Navien Water Heaters

Navien’s Premium Tankless Gas Water Heaters are available for both residential and commercial use. Unlike traditional tank water heaters, Navien tankless heaters provide an endless supply of hot water any time you need it. Navien’s next-generation condensing tankless technology is designed to simplify every installation and offer the best hot water experience. It eliminates the tankless obstacles of the past, making it an ideal solution for tank replacements. Simple retrofit, ultra high condensing efficiency and now field gas convertibility all combine to make the NPE series easily the best choice in tankless.

Step 1: Determine the maximum number of devices you want to run and their total flow rate. Then, add up their flow rates (gallons per minute). This is the desired flow rate you’ll want for the demand water heater.
Step 2: Determine required temperature rise. To determine temperature rise, subtract the incoming water temperature from the desired output temperature. Unless you know otherwise, assume that the incoming water temperature is 50°F (By using a low temperature assumption you ensure that you will not undersize your tankless unit. If you live in a warm climate your water temperature will likely be much higher.) For most uses, you’ll want your water heated to around 105–115°. In this example, you’d need a demand water heater that produces a temperature rise of 55°.
Step 3: Sizing Example: An average shower will be between 104–106° and uses 2.6 gallons of water. Assuming your water temperature is 40° coming into your home, and you want to produce enough hot water to run 2 showers at the same time.
Step 4: How much hot water do you need at one time? Do you need to run 2 showers at the same time or maybe a shower and a couple sinks? The chart below shows the range of water usage range and average water temperatures for various fixtures. We suggest using 2.5 gpm for a shower and 1.0 gpm for a bathroom as a reference point in determining your total simultaneous water needs.

Fixture Average Flow GPM Avg. Temp.
Tub: 4.0 102°F
Shower: 2.5-3.0 104°F
Washing Machine: 2.0 120°F
Dishwasher: 1.5 110°F
Kitchen Sink: 1.5 110°F