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Natural Gas: Pressure Settings

After 24 years servicing residential comfort systems, I encountered a situation I didn't know existed. It turned into a project spanning 3+ months. I will spare you many details, but provide information that can help.

Natural Gas Distribution Systems

Natural gas distribution pressures can range from 60 psi to 1/4 psi (4 ounces). While the gas company thinks in terms of psi or ounces of pressure, repairmen use inches of water column ("WC). To go from ounces to water column, multiply by 1.64.

High Pressure Residential Distribution

In College Station/Bryan, most meters are pressurized to 15"WC. At the meter, a pressure regulator reduces the pressure to a 5-7"WC range which is what you will see coming into the 24V gas valve. At the furnace manifold, during actual heating, one can expect 3.5"WC.

Low Pressure Residential Distribution

I will use an older College Station neighborhood for my illustration. It is bounded on the North by George Bush, on the South by Park Place, and on the East by Lee St. All homes are fed from a central regulator system located on Burt St. between Suffolk and Dexter.

The primary regulator is set at 5.25 ounces (8.6"WC) and a backup regulator is set at a slightly lower pressure. Each home on the system has a meter that does NOT have a regulator. As a result, pressures decrease as one gets further from the central regulator.

My experience was with a home on Pershing that was fairly close to the central regulator, and I measured 8.6"WC coming into my 24V gas valve, but the furnace was over firing and a roll-out switch would trip after 3 minutes.

Why the Tripped Roll-out Switch?

I believe that most gas fired equipment in this neighborhood is being over fired, but generally the equipment will handle the extra stress.

On Pershing, January 1993, I installed a Rheem furnace. In 14 years I had encountered no firing problems. After the roll-out switch tripped, I measured pressures at the 24V gas valve. The actual readings were well outside specification, so I installed an in-line appliance regulator. I quickly discovered the 24V gas valve was faulty, so I made the replacement. Then I measured pressures again.

Wow!

The above seems pretty simple, but the confusion surrounding this project was amazing.

I didn't know there was such a thing as a low pressure central distribution system, and I wasn't alone.

Rheem recommended the in-line regulator, but no one knew where I could get one. I tried one plumbing company, three plumbing supply houses, one AC supply house, one appliance store, and one fireplace outlet, but to no avail. I decided to try the internet, but good fortune intervened, and I finally found one locally.

While at Johnson Supply, I said to Norm, "You're not going to have this, but here's what I need." Norm immediately produced the pressure regulator I was seeking. It has 1/2" pipe threads, is adjustable, and handles incoming pressures up to 15"WC. I had no trouble adjusting my gas pressure from 8.6"WC (incoming) to 6"WC (outgoing).

Choices

Hindsight is always better than foresight. I probably could have replaced the faulty 24V gas valve with a new one, left it in an over-fired condition, and it would have worked. I had two variables floating at the same time, and felt it wise to start with the correct inlet pressure before proceeding.

There are five other furnaces in that neighborhood, I installed years ago. I believe they are operating in an over-fired condition, but I choose to leave well enough alone. If I encounter a similar problem in the future, I will first add a regulator.

As I see it, the best solution would be for the gas company to convert the entire neighborhood to the high pressure system I described at the beginning of this article.

Kool Ways to Keep Warm,

Dr. Kool

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