intertherm standing pilot propane burner Heat Rise of 38°F spread.

[justplumducky]

Model: MGHA077 ABFC
Serial: MGH9703 05880

20-yr. old furnace. Data plate "Nominal Heat Rise" = 70°F
Actual heat rise currently is 38° spread. Spread is 77 - 115°F

LPG company adjusted supply pressure (inlet of gas valve) to 12" w.c. I tried to get him to adjust the supply pressure to 13" w.c. which is the spec on the furnace's data label, but his company policy is to adjust all their tank regulators to 12" w.c. However, he did say he wouldn't say anything to anyone if I were to adjust the supply pressure to 13 or a maximum of 14" w.c.

Could not connect manometer to OUT PRESS port and calibrate to 11" w.c., because the the Allen screw/plug in the OUT PRESS port is stripped. Just posted another thread asking how to remove that stripped hex screw.

Going back in the near future to remove that screw... successfully I hope (gas valve is 23 yrs. old), but since the operating pressure at the inlet side of the gas valve is 11" w.c., I'm wondering if there's a usual amount of pressure loss as the gas goes thru the valve. In other words, how much it could be expected to drop from the 11" w.c. at the inlet side of the valve, while the valve is operating/heat turned ON.