HI Plumber cheat sheet

Air test pressure for DWV systems is typically 5 psi (34.5 kPa) held for 15 minutes with no drop; water test uses 10 ft (3 m) head above highest pipe.

A trap seal depth of 2 to 4 inches (51–102 mm) prevents sewer gas; 4 inches (102 mm) is the maximum permitted seal depth.

Before entering a confined space, test for oxygen (19.5–23.5%), LEL (<10%), H2S (<10 ppm), and CO (<35 ppm); ventilate continuously.

Pipe dope and PTFE tape are not interchangeable on gas lines; use only listed gas-compatible sealants and never use tape on flare fittings.

Hot water at fixture outlets must not exceed 120°F (49°C) for domestic use; scald protection is required in public facilities.

A backflow prevention device must be tested annually; reduced-pressure zone (RPZ) assemblies require testing by a certified tester.

Always support pipe at intervals: copper horizontal ≤6 ft (1.8 m), PEX horizontal ≤32 in (813 mm) and vertical ≤10 ft (3 m) per manufacturer.

Water closet flush volume ≤1.6 gallons per flush (6 Lpf) for new installations; urinals ≤1.0 gpf (3.8 Lpf).

Lavatory faucet maximum flow rate is 2.2 gpm (8.3 L/min) at 60 psi; kitchen faucets also 2.2 gpm.

A water closet must be installed with a minimum 15-inch (381 mm) centerline to side wall and 21 inches (533 mm) front clearance.

Shower valves must be pressure-balancing or thermostatic to limit temperature fluctuations; maximum outlet temperature 120°F (49°C).

Fixture units (FU) are used to size drainage and supply; a water closet counts as 3 FU drainage and 10 FU supply (private).

Floor drains require a trap primer or trap seal protection when the trap may evaporate; trap seal depth minimum 2 inches (51 mm).

A fixture's tailpiece must extend at least 2 inches (51 mm) below the fixture; a continuous waste may serve up to two fixtures.

Drainage pipe slope: 2% (1/4 inch per foot) for 2-inch (50 mm) and smaller; 1% (1/8 inch per foot) for 3-inch (80 mm) and larger.

A vent stack must extend at least 6 inches (152 mm) above the roof or 12 inches (305 mm) where snow accumulation is expected.

Maximum trap arm length: 2-inch pipe = 5 ft (1.5 m) for 1.5-inch trap; 3-inch pipe = 6 ft (1.8 m) for 2-inch trap.

A building drain must have a cleanout at the junction of the building sewer and at intervals not exceeding 100 ft (30.5 m).

Horizontal drainage pipe must be supported at intervals not exceeding 4 ft (1.2 m) for 2-inch and smaller, 10 ft (3 m) for larger.

A vent must rise vertically at least 6 inches (152 mm) above the fixture before offsetting horizontally.

The drainage fixture unit (DFU) load for a 3-inch building drain is 42 DFU; a 4-inch building drain is 216 DFU.

Minimum static water pressure at a fixture is 8 psi (55 kPa); maximum static pressure is 80 psi (552 kPa).

Pressure-reducing valve required when street pressure exceeds 80 psi (552 kPa); set to 50–60 psi (345–414 kPa).

Water supply pipe sizing uses fixture units (WSFU) and equivalent length; a 1/2-inch tube supplies up to 6 WSFU at 60 psi.

Thermal expansion control is required on a closed system; install an expansion tank sized to system volume.

Hot water distribution: recirculation or heat-traced lines keep hot water within 5 seconds at the farthest fixture.

Backflow prevention: air gap is the highest protection; RPZ for high hazard; double check for low hazard.

Water heater temperature and pressure relief valve discharge pipe must terminate 6–24 inches (152–610 mm) above floor and not be trapped.

A plumbing permit is required before installing, altering, or repairing a plumbing system; exemptions vary by jurisdiction.

The IPC and UPC are model codes; local amendments govern. Always verify the adopted edition with the authority having jurisdiction (AHJ).

A plumbing inspector must be given access to inspect rough-in, water test, and final; approvals must be obtained before concealment.

A backwater valve is required on a building sewer subject to backflow; it must be accessible for maintenance.

A plumbing license is required for contractors; a journeyman license is required for individuals performing plumbing work.

Code requires a minimum 1-inch (25 mm) air gap for indirect waste receptors or a 2-inch (51 mm) air gap for floor drains.

A water heater must be anchored, strapped, and have a pan with drain when installed in an attic or ceiling space.

Labor cost = hourly wage × labor burden (typically 1.25–1.65) × hours; burden includes taxes, insurance, and benefits.

Overhead and profit (O&P) are added separately: overhead covers indirect costs; profit is a percentage of total cost.

A change order must be written and signed before work proceeds; it should state scope, price, and schedule impact.

Retainage is typically 5–10% withheld until substantial completion; track it as accounts receivable.

Estimate material waste factors: 5–10% for pipe, 10–15% for fittings, and include consumables like solder and primer.

A takeoff must include fixtures, pipe, fittings, valves, hangers, insulation, and equipment; verify quantities against plans.

Break-even point = fixed costs ÷ (unit price − variable cost per unit); use to set minimum job pricing.