If you are considering installing a tankless water heater in your new home or replacing your existing conventional water heater with an energy efficient tankless water heater, you have probably been attracted by a combination of energy savings and the promise of “endless hot water.” However, properly sizing a tankless water heater is important to take advantage of these attributes of tankless water heaters. If your water heater is too small, you will end up with “endless lukewarm water.” On the other hand, buying one that is too large is just a waste of money and reduces your savings.
To choose the correct size demand water heater, you need to know two three thing: the temperature of the cold water as it enters your home, the temperature you need the hot water to reach, and your flow rate. Flow rate is the maximum number of gallons of hot water you expect to use per minute. For example, if you want to be able to take a shower at the same time you are doing laundry, add up the gallons of hot water used per minute by your washing machine and in your shower.
Once you have the flow rate, subtract the temperature of the cold water from the temperature desired for the hot water keeping in mind that the temperature of the cold water entering your home may vary throughout the year. Use the lowest expected temperature. This calculation will give you the necessary temperature rise.
Look for a demand water heater that can provide the necessary temperature rise at the desired flow rate. By choosing an appropriately sized demand water heater, you can maximize energy efficiency without sacrificing performance.
