A gas line must reach a rooftop unit from a meter located at grade. Which routing is acceptable under the fuel gas code?
- AInside a return air plenum, provided the pipe is welded steel with no fittings in the plenum
A return air plenum is a circulating air path. A leak there would be distributed through the entire duct system, so gas piping is prohibited regardless of joint type.
- BUp the inside of an abandoned masonry chimney flue
Chimneys and gas vents are named prohibited locations. Abandoning the flue does not change the classification, and the shaft would trap escaping gas.
- Up the exterior wall of the building, supported and protected against physical damage
- DUp the elevator hoistway, strapped to the guide rail brackets
Elevator and dumbwaiter shafts are prohibited locations. They are enclosed vertical shafts with arcing equipment and no way to detect an accumulation.
Why C is correct
An exterior riser is outside every prohibited shaft and duct, so a leak dissipates to open air rather than being carried into occupied space. The code's conditions on that routing are support at the required intervals, protection where vehicles or equipment could strike it, and protection from corrosion, all of which are achievable on a wall.
What this question is testing
This tests recall of the prohibited-location list and whether you can spot that a plausible-sounding qualifier, such as welded joints, does not create an exception.
On the job
Existing chimneys look tempting on retrofit work because the chase already goes to the roof, and crews have been caught doing it. The exterior route is more labor but is what gets approved. Once outside, the details matter: hangers or straps at the code spacing, a coating or wrap where the pipe passes through a wall or contacts masonry, and bollards or a sleeve where a truck could hit the riser at grade. Some jurisdictions also want the riser painted the utility's identification color.
Memory technique
Anything that moves air or moves a car has no business carrying gas pipe.
Exam tip
Ducts, chimneys, chutes and shafts are all off limits. No joint type or condition buys you a way in.
Where to look it up
Prohibited locations for gas piping are in IFGC Chapter 4, Section 404.3. UPC jurisdictions apply UPC Chapter 12 or NFPA 54, which lists similar but not identical locations.