Gas Line Sizing For Gas Tankless Water Heaters

Check to make sure your gas line is sized properly.  Tankless water heaters draw many more BTU's than a tank water heater, so you will want to make sure your gas line is of the proper size and the distance the gas line is run is not too long, so the unit will function properly.  Below are tables that show the maximum gas line run by diameter for natural gas, propane (LP) with black iron pipe and propane (LP) with copper tubing.  If any other applications are sharing the line or for more specific information, please consult the National Code Fuel Chart.

Maximum length of black iron pipe run for Natural Gas

Model	Nominal Iron Pipe Size (diameter)
	3/8"	1/2"	3/4"	1"
Bosch 38B	20 ft	80 ft
Bosch 1000P	5 ft	20 ft	100 ft
Bosch 1600P/125B, Bosch 1600H/125HX		10 ft	40 ft	150 ft
Bosch 1600F/125FX		10 ft	40 ft	125 ft
Bosch 2400E, 2400EO/250SX	Not recommended		20 ft	70 ft

Important Factors to Consider

Gas Venting Requirements
Gas Line Sizing Requirements
Gas Combustion Air Requirements