Originally Posted by

**Bob999**
A VERY large input BTU will be required with tankless heaters. If you assume 20 gpm of 108 F water and 57 F incoming that is a temperature rise of 51 F. So the hourly BTU input required is 20 gal times 8 lbs/gal times 51 degrees times 60 minutes equals 490,000 BTU/hour. If you assume the water heater is 80% efficient then the gross input per hour is 490k/0.8 = 612,000 BTU. Getting the required propane flow to support an input of that size will require a very large propane tank.

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