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CT Plumber: Fuel gas piping and appliances

CT Plumber · Work through your exam, one topic at a time.

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Fuel gas piping and appliances

Domain 9 - Fuel gas piping and appliances

This domain covers gas piping materials and sizing, testing, connectors, appliance venting, combustion air, and bonding. Expect one sizing calculation and several installation-rule items.

Piping and sizing

  • The longest-length method sizes each section for the total load downstream and the distance from the meter to the farthest outlet, using the table's pressure drop, typically 0.5 in. w.c. for natural gas at 0.60 specific gravity. Longest-length and branch-length methods are not interchangeable.
  • Materials: black steel with listed fittings, corrugated stainless steel tubing (CSST) per manufacturer requirements with bonding, and copper only where permitted for the gas type. No piping in elevator shafts or return-air plenums, and nothing concealed so it cannot be inspected.
  • A shutoff valve is required in the same room as the appliance, with a sediment trap (drip leg) downstream of the valve ahead of the controls.
  • Gas piping must be bonded to the grounding electrode system.
  • Testing: air test at 1½ times working pressure, minimum 10 psi, held at least 10 minutes before the meter is set. Never test against the meter.

Appliances and venting

  • A flexible appliance connector may not exceed 6 ft, may not be concealed, may not pass through a wall, floor, or ceiling, and may not be reused.
  • Category I appliances use a draft hood and vent connector with termination at least 5 ft above the draft hood and 2 ft above anything within 10 ft.
  • Combustion air comes from the indoor-volume method or openings. A tight house with a large exhaust fan or range hood can depressurize and backdraft a draft-hood appliance.

Worked example

Load: 100,000 Btu/hr furnace + 40,000 Btu/hr water heater + 65,000 Btu/hr range = 205,000 Btu/hr ≈ 200 cfh at about 1,020 Btu/ft³. The longest run from the meter to the furnace is 40 ft. At 0.5 in. w.c. in the natural gas table, 1 in. pipe at 40 ft is about 220 cfh, which is marginal once fittings and future load are considered; 1¼ in. gives roughly 460 cfh at 40 ft and is the safer answer. Then add a shutoff valve and sediment trap at each appliance.

Where marks are lost

  • Sizing by branch length when the longest-length method applies.
  • Breaking the connector rules: over 6 ft, concealed, or through a wall.
  • Forgetting bonding requirements for CSST.