In the picture below is a gas fired hot
water boiler, the silver thing the black pipe is
connected to is a Honeywell gas control valve
for the boiler. The black pipe is the gas pipe
supplying gas to the gas control valve. The
problem here is the black pipe coming into the
boiler is smaller then the inlet size of the gas
valve. Gas control valves require X amount of
gas, a smaller gas line may not provide enough
gas for the boiler to run properly, causing a
possible carbon monoxide problem, carbon
monoxide is a gas that comes from any fuel that
is not burning properly. if the gas supply is
not right it will not burn right and cause
carbon monoxide to build up.
Note: this boiler hook up was ok because the smaller gas pipe delivered above the minimum requirement of the boilers needs.