Everything You Need to Know about Gas Piping

Alan Carson July 11, 2017

The beginning of October means many homeowners living in the northern part of the country will have to start firing up their heating systems. Natural gas is among the least expensive and most efficient ways to fuel a furnace or boiler. Along with its advantages come safety concerns and responsibilities for homeowners. As a home inspector, it is your job to help identify deficiencies that can compromise the safety of occupants in homes using natural gas. We will discuss some of the basics of inspecting gas piping.

Supply, branch and drop lines or risers

The piping inside the house is called the gas supply line or building line. Branch lines run to individual appliances. The branch line terminates in a drop line, which is a vertical pipe dropping down to the appliance from an overhead branch line. This drop line is called a riser if it carries gas up to an appliance from a branch line below the appliance.

Sediment trap, dirt pocket or drip leg

At the appliance connection point, there usually is a sediment trap or dirt pocket, sometimes called a drip leg that includes a nipple and a cap. This pipe extension usually is at least 3 inches long and is intended to catch any water or foreign material that may be in the gas before the material gets into the appliance itself. This is simply a gravity system, with the solids and liquids falling into the pocket.


Pipe downstream of meter is homeowner’s

The piping downstream of the gas meter usually is the responsibility of the homeowner. The piping upstream of the gas meter and the meter itself usually are the responsibility of the gas company.

Piping materials

Steel, copper, brass: The most common gas piping is black steel. Galvanized steel, copper, brass or CSST (Corrugated Stainless Steel Tubing) also can be used in some areas, but some utilities specifically prohibit the use of copper. In other areas, the use of copper is widespread. You should know what is acceptable in your area. Steel piping typically is black with malleable iron or steel fittings. Galvanized steel is used in some areas as well.



Flex connectors: Flexible connectors are permitted to connect appliances to the gas piping. There has to be a shut-off valve at the connection to the rigid piping. This valve has to be in the same room as the appliance.

Three- or six-foot long and accessible: The flexible connectors can’t go through walls, floors or ceilings, nor can they be concealed. The flexible connector length usually is limited to 3 feet except for gas ranges and clothes dryers. For these appliances, 6 feet generally is allowed. Splicing or joining connectors with nipples often is prohibited. In some jurisdictions, flexible connectors are allowed only for gas ranges, dryers, outdoor barbecues and other semi-portable appliances. Flexible connectors may not be permitted on gas furnaces, water heaters, space heaters, etc. In areas prone to earthquake, flexible connectors are more likely to be used on all appliances since they provide some measure of protection against gas piping leakage or rupture during an earthquake. Check your local gas code to determine what is or isn’t allowed in your area.

Thread seal tape

Thread seal tape (often mistakenly referred to as Teflon® tape) that is white in color is not recommended as a joining compound for steel gas piping. Cutting oils that remain on the pipe threads from manufacture may prevent the tape from sealing. In some areas, yellow thread seal tape is allowed. Pipe dope is preferred and may be all that is allowed. You may want to check with the gas utility. Ask whether you should report as a defect any piping installations with thread seal tape of any color.



Not in ducts

Gas piping can’t be run through chimneys or duct systems.

Shut-off valve

Although there are some exceptions, most appliances should have a shut-off valve adjacent to them.

Bonding gas piping

Most authorities do not allow the use of gas piping as a grounding means for the electrical service. Bonding the gas piping to the electrical grounding system is a requirement, however, in many jurisdictions. Often, this is done by attaching the gas piping to the supply water piping (assuming it is grounded) frequently near the water heater. To prevent an electrical potential buildup within the gas piping that could lead to arcing, which might ignite gas, we want to keep the gas piping at zero electrical potential by bonding it to the grounding system.

The following problems are typical on gas piping:

  1. Leaks
  2. Inappropriate materials
  3. Inadequate support
  4. Rusting
  5. No drip leg
  6. Missing shut-off valve
  7. Improper connections
  8. Plastic pipe exposed above grade
  9. Piping in chimneys or duct systems
  10. Copper tubing not properly labeled

The implications of all of these problems are possible gas leaks and explosions.

We have discussed some of the basics of gas piping that home inspectors should have a good understanding of in order to identify potentially unsafe situations. We also have listed ten conditions that are typical when there are problems with gas piping. A detailed explanation on the causes, strategies for inspecting, and implications can be found in the ASHI@Home training program.

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