Gas line pressure

[DanW13]

I noticed recently there has been a number of post reagarding inlet gas pressure to the furnace. So I thought I would ask this question as I am just curious. When you have a new furnace installed such as mine Infinity 58MVC should the installer have to adjust the inlet gas pressure or is the pressure automatically adjusted when the gas flows thru the manifold(s) ?

[hearthman]

Uh, the inlet pressure is the pressure in the house piping. The manifold pressure is what's sent to the burners. The inlet pressure is determined by the pressure supplied at the meter less the pressure drop from piping runs and other appliances firing. You cannot/ do not adjust inlet pressure except in a medium pressure system where you install an MP regulator upstream of the appliances. Manifold pressure should be set to mfrs. specs. If your inlet pressure is too low, map out the gas piping first. If the piping sizing/ layout is acceptable, then you might be able to get the gas utility to increase the pressure at the meter. If your inlet pressure is too high, you install an MP regulator just upstream per the IFGC.

A tech should test the inlet pressure on a new install to verify it is within spec. and this test should be under full load with everything in the house firing. He should then check the manifold pressure to ensure it is firing within spec. Then, perform combustion analysis and adjust within mfrs. specs.
HTH,