Question: What is the recommended amount of gas pressure for a fireplace gas valve? I know that most recommend a maximum of 1/2" psig, or 13.5 inches water column, but what is the optimum range. Answer: Depends on the particular appliance. Some units actually have a small regulator before the gas valve, so they make certain the gas is stepped down to the best pressure. Also, volume (or flow) is very important, you could have the correct pressure but not enough delivery. This is mainly a function of pipe size. Your exact question is not so easily answered. For best flame height, a pressure near the top end would be better. If pressure is low, some manufacturers will substitute a larger drilled orifice (vented log sets only) to make up for the pressure. Gas pressure is so low that a small change in pressure (+-10%) is not likely to make a big difference in performance. In any case, delivered pressure is not something that is adjustable by the customer. If you other gas appliances (range, furnace, hot water heater) work, you can be assured that you are in the correct range. Link: Article about Gas and Pressure, etc.