Final Gas System Rough-In Lab and Inspection Simulation
Objective. The student will install a complete residential gas rough-in on a training wall assembly according to a provided plan, conduct a pressure test, and pass a simulated rough-in inspection conducted by the instructor acting as the authority having jurisdiction.
Final Gas System Rough-In Lab and Inspection Simulation
What This Lab Is About
This lab brings together every skill you have practiced in this course. You will read a dimensioned isometric drawing, size pipe for a two-appliance residential gas system, cut and thread black steel pipe, install the rough-in on a training wall, conduct a pressure test, and then stand in front of your instructor — acting as the authority having jurisdiction (AHJ) — and defend your work. This is the same sequence a journeyman plumber follows on a real job site before a rough-in inspection.
Understanding the Isometric Drawing and Load Schedule
Your drawing packet includes a dimensioned isometric and a load schedule that lists the BTU/h input rating for a residential water heater and a range. Before you touch a wrench, you must:
1. Read the load schedule and identify the maximum BTU/h demand at each outlet and at the meter.
2. Trace each pipe segment on the isometric and record its length.
3. Use the longest-length method — find the longest straight-line run from the meter to the farthest appliance, add all equivalent lengths for fittings on that run, and use that total equivalent length to enter the capacity table for your local gas type and inlet pressure.
4. Select the pipe size for each segment. Each branch must carry only the load beyond that point; the main must carry the combined load.
5. Submit your material list to your instructor before pulling any pipe or fittings. This step mirrors the plan-review stage of a real permit.
Cutting and Threading Black Steel Pipe
Residential gas piping in most jurisdictions is installed in Schedule 40 black steel pipe. The steps are:
- Measure twice, cut once. Account for thread engagement when cutting — pipe screws into fittings, so your cut length is shorter than the face-to-face dimension on the drawing.
- Deburr the cut end inside and out before threading.
- Thread with a ratchet or power threader to the correct NPT thread count for the pipe size. Inspect threads: they should be clean and tapered with no torn crests.
- Apply gas-rated thread sealant (pipe dope listed for gas service, or PTFE tape listed for gas) to the male threads only, starting one thread back from the end.
- Make up joints hand-tight, then wrench-tight. Do not back off a joint once tightened; back-off breaks the sealant seal.
Installing Supports, Valves, and Drip Legs
Supports: Black steel pipe must be supported at intervals required by the applicable code — consult the code table for your pipe size. Use approved pipe hangers or straps. Do not let pipe rest on electrical conduit, ductwork, or other trades' work.
Shutoff valves: Each appliance must have a dedicated shutoff valve located within reach of the appliance and upstream of the flexible connector or union. Ball valves are the standard choice for gas service; use valves listed for gas.
Drip legs (sediment traps): Install a drip leg at each appliance connection. A drip leg is a capped nipple extending downward from a tee, positioned so that any moisture or debris in the gas stream falls into the cap rather than entering the appliance valve. The standard configuration is a tee in the supply line, a nipple dropping from the bottom, and a cap on the nipple.
Pressure Testing the Rough-In
Before the inspection, you must pressure-test the entire rough-in with the appliance outlets capped. Steps:
1. Cap all open outlets — appliance connections and any test ports not in use.
2. Connect an air supply and a calibrated pressure gauge to the system. Never use an open flame or oxygen to test gas piping.
3. Charge the system to the test pressure required by the applicable code for a residential low-pressure gas system. The test pressure must exceed the operating pressure by the margin specified in your code.
4. Hold the test pressure for the time period specified. Monitor the gauge; the reading must not drop.
5. Document the test: record the date, test medium (air), test pressure, hold time, result (pass/fail), and your name. This documentation becomes part of the inspection package.
6. Locate any leaks with a listed gas leak detection solution or a non-corrosive bubble solution — never with a flame.
Safety During This Lab
- Eye protection and gloves are required when cutting and threading pipe. Steel chips from the threader are sharp.
- Lockout/tagout the air compressor before connecting or disconnecting fittings if the line is under pressure.
- Never use natural gas or LP for testing — use air or an inert gas. A pressurized gas system in an enclosed shop is a serious ignition and asphyxiation hazard.
- Keep the work area clear of trip hazards; pipe lengths and the floor vise create obstacles.
- Report any equipment malfunction — a defective gauge gives a false pass and is a safety hazard in the field.
The Simulated Inspection
Your instructor will follow an inspection checklist covering: pipe material and listing, support spacing, valve locations, drip leg installation, test pressure used, test documentation, thread quality (spot-check), joint sealant application, and clearances from electrical panels or ignition sources. You must be able to state the code basis — by topic, not necessarily by exact section number — for every choice you made. Practice answering like this: "The support spacing is based on the code table for half-inch steel pipe, which requires a support every six feet." One deficiency may be corrected on the spot. Two or more deficiencies require full rework and a re-inspection.
Key terms9
Worked examples4
- Identify the actual measured pipe length of the range branch: 22 feet.
- List the fittings on the range branch: two 90° elbows and one tee (run).
- Calculate equivalent length for two 90° elbows: 2 × 2 ft = 4 ft.
- Calculate equivalent length for one tee (run): 1 × 1.5 ft = 1.5 ft.
- Sum all equivalent lengths: 22 ft + 4 ft + 1.5 ft = 27.5 ft.
- Enter the capacity table at a total equivalent length of 27.5 ft (round up to the next table row if 27.5 is not listed).
- Identify each appliance load: water heater = 36,000 BTU/h; range = 65,000 BTU/h.
- The water heater branch must carry 36,000 BTU/h.
- The range branch must carry 65,000 BTU/h.
- The main from the meter to the first tee must carry the combined load: 36,000 + 65,000 = 101,000 BTU/h.
- Identify the face-to-face distance: 4 inches.
- Identify thread engagement per end: 0.75 inches.
- Total thread engagement for both ends: 2 × 0.75 in = 1.5 in.
- Cut length = face-to-face distance + total thread engagement = 4 in + 1.5 in = 5.5 in.
- Cut the nipple to 5.5 inches so that after threading and making up both joints the face-to-face dimension is 4 inches.
- Record starting pressure: 15 psi.
- Record ending pressure after hold period: 14.2 psi.
- Calculate pressure drop: 15 psi − 14.2 psi = 0.8 psi.
- A pressure drop of any amount during the required hold period indicates leakage — the system fails the test.
- Locate the leak using listed bubble solution, repair, and retest before calling for inspection.
The math in this lesson2
Materials: Training wall assembly, black steel pipe and fittings (all sizes per student design), pipe threader, cutters, pipe vise, gas-rated sealant, ball valves, pressure gauge, air supply, pipe hangers, isometric drawing packet, inspection checklist, lab log
Check: Formal inspection checklist scored by instructor: all mandatory items (material, supports, valve placement, drip legs, test documentation) must be satisfactory. One deficiency may be corrected on the spot; two or more deficiencies require a re-inspection after rework. Lab log of all lessons reviewed for completeness.
Practice check8
Answer each question, then check it. Nothing is recorded; this is your own practice.
