Gas Supply If this is a new installation make certain that the fuel gas lines are aggressively and completely purged of air, liquid, and debris. Because of the small volume flowing through the heater, it can take a very long time to purge the lines with the heater gas train connected. Verify gas pressure to the heater. Natural gas fueled heaters should receive 4 ½ inches of water column pressure. LPG fueled heaters should receive 11 inches of water column pressure. It is important that this pressure be verified with a gauge or manometer. Check the pressure with gas flowing