Fuel storage and distribution systems
Residential water heating and HVAC systems use three gas and liquid fuels: fuel oil, natural gas, and propane. Propane and fuel oil must be stored in tanks. Each must be carried to the fuel-fired appliance, from the storage tank or, for natural gas, from the gas meter. This must be done with no margin for error. A leak of a combustible fuel very likely causes catastrophic damage, and loss of life is possible.
The IRC applies after the point of delivery. Before it, US DOT rules apply to natural gas, and NFPA 58 applies to propane.
Upstream of the point of delivery, gas pipes are usually concealed, and local building codes do not cover them. A home inspection therefore does not include them.
Black steel gas pipe
Color and rigid form may be used to identify black steel gas pipe. It usually comes in 10 foot sections. Common diameters range from 1/2 inch to 1-1/2 inches, in 1/2 inch steps. The pipe should be no lighter than Schedule 40.
Joints are usually threaded, and the threaded part of the pipe end should be about 3/4 to 1 inch long. During an inspection, this can be difficult to detect visually. Pipe joint compound, also called pipe dope, or yellow Teflon tape should cover the threads of gas pipe joints. White Teflon tape, the kind used on water pipe joints, is not acceptable on gas pipes.
Black steel pipe should be held by hangers, straps, or clamps of a compatible metal. Copper should not be used for hangers. Horizontal support spacing is 6 feet at 1/2 inch, 8 feet at 3/4 inch and 1 inch, and 10 feet at 1-1/4 inch and larger. Proper support keeps stress off gas pipe and its fittings.
Copper gas tubing
The annealed, or flexible, coil form is often used for copper gas tubing. Rigid copper is also used. The tubing should be Type K, with green labels, or Type L, with a blue label.
Excessive hydrogen sulfide in a gas supply can corrode copper, so copper gas tubing should not be used where the supply contains it. Some areas do not allow copper gas tubing, and home inspectors working there should be aware of it.
Four fitting types may be used at copper joints: threaded, brazed (not soldered), flared, and crimped. Flared fittings are usually on annealed tubing only. A crimped joint uses a special fitting listed for gas.
Copper tubing supports should be a compatible metal and not steel. Horizontal support spacing is 4 feet at 1/2 inch, 6 feet at 3/4 inch and 1 inch, and 8 feet at 1-1/4 inch and larger.
Copper gas tubing can be confused with water supply tubing, so it should be identified with a yellow label printed with GAS, applied at intervals of 5 feet or less.
Corrugated stainless steel tubing
Corrugated stainless steel tubing (CSST) is flexible and comes in coils. Polyethylene sheathing covers the corrugated tube, commonly in yellow, black, or orange. Common diameters match those of black steel pipe.
CSST is frequently confused with a flexible appliance connector (FAC). CSST distributes gas, and an FAC connects an appliance to the gas supply. CSST usually has the larger diameter. FACs are commonly 3/8 or 1/2 inch in diameter and usually 12 to 72 inches long. CSST fittings are installed in the field, and FAC fittings at the factory, on both ends. Corrugation shows on an FAC; sheathing hides it on CSST.
Installation of CSST, a manufactured system, must follow the manufacturer's instructions, which can vary between manufacturers and between types of CSST. Typical horizontal support spacing is 6 feet at 1/2 inch and 8 feet at 3/4 inch and larger. The typical recommended bending radius is 3 inches at 3/4 inch and smaller and 5 inches at 1 inch and larger.
Appliance cabinets and masonry fireplaces may usually receive CSST. All valves and fittings, sediment traps included, should be installed as recommended. A factory-built fireplace should not receive CSST; this rule is a recent change. A moveable appliance, such as a clothes dryer or a range, may not connect directly to CSST. The CSST should end at a properly secured fitting, and an FAC should run from that fitting to the appliance.
Most CSST should be bonded, for lightning safety, to the grounding electrode conductor. The connection may be made at any point on the grounding electrode system, between the service equipment and a grounding electrode. The bonding conductor should be copper, at least #6 AWG. It starts at the first hard pipe length at the house or the first fitting joining CSST to the gas service pipe.
Some CSST, Flash-Shield and Counterstrike among them, does not require bonding. A local building official may still require it. CSST the manufacturer does not require to be bonded usually has black sheathing. CSST that requires bonding usually has yellow or orange sheathing.
Numbers and Rules to Memorize
| Item | Value |
|---|---|
| Fuels for residential HVAC and water heating | Fuel oil, natural gas, propane |
| Gas pipes upstream of the point of delivery | Usually concealed; outside local building codes and the home inspection |
| Rules after the point of delivery | IRC |
| Rules before the point of delivery | US DOT for natural gas; NFPA 58 for propane |
| Black steel section length | Usually 10 feet |
| Black steel and CSST common diameters | 1/2 to 1-1/2 inches, in 1/2 inch steps |
| Black steel pipe | Should be Schedule 40 or heavier |
| Threaded length of a black steel pipe end | About 3/4 to 1 inch |
| Thread sealant on gas pipe | Pipe joint compound or yellow Teflon tape |
| White Teflon tape on gas pipe | Not acceptable |
| Black steel horizontal support | 6 ft at 1/2 in; 8 ft at 3/4 and 1 in; 10 ft at 1-1/4 in and larger |
| Hanger metal not to use on black steel | Copper |
| Copper gas tubing types | Wall thicknesses Type K (green labels, the thicker wall) or Type L (blue label) |
| Excessive hydrogen sulfide in the supply | Copper should not be used |
| Copper joints | Threaded, brazed (fused with a mostly silver alloy above 800 degrees F, stronger than soldering; not soldered), flared (usually annealed only), crimped (listed for gas) |
| Copper horizontal support | 4 ft at 1/2 in; 6 ft at 3/4 and 1 in; 8 ft at 1-1/4 in and larger |
| Hanger metal not to use on copper | Steel |
| Copper gas tubing label | Yellow, printed GAS, at 5 foot intervals or closer |
| CSST sheathing colors | Yellow, black, orange |
| FAC common diameters | 3/8 and 1/2 inch |
| FAC length | Usually 12 to 72 inches |
| Fittings | CSST: field installed; FAC: factory installed, both ends |
| Corrugation visible | On an FAC, not on CSST |
| CSST horizontal support, typical | 6 ft at 1/2 in; 8 ft at 3/4 in and larger |
| CSST bending radius, typical | 3 in at 3/4 in and smaller; 5 in at 1 in and larger |
| CSST in appliance cabinets and masonry fireplaces | Usually allowed; valves and fittings as recommended |
| CSST in a factory-built fireplace | Should not be installed; a recent change |
| CSST to a moveable appliance | Not directly; secured fitting, then an FAC |
| CSST bonding, for lightning safety | Grounding electrode conductor; most CSST should be bonded |
| Bonding connection point | Anywhere on the grounding electrode system |
| Bonding conductor | Copper, #6 AWG minimum |
| Bonding conductor start | First hard pipe length at the house, or first fitting joining CSST to the gas service pipe |
| Bonding not required by the manufacturer | Flash-Shield, Counterstrike; a local official may still require it |
| Sheathing color and bonding | Black: usually not required; yellow or orange: usually required |