NITC Master Plumber cheat sheet

Fixture units (FU) convert dissimilar fixtures to a common load measure; 1 FU = 1 gpm (0.06 L/s) of drainage or supply demand for sizing purposes.

Hunter's curve relates total fixture units to probable peak flow; peak demand is far below the arithmetic sum of fixture flows because of non-coincident use.

Minimum building drain slope: 1/4 in per ft (2%) for pipe 4 in and smaller; 1/8 in per ft (1%) for 5 in and larger where solids transport is verified.

Horizontal drainage branch length limits: 1-1/2 in pipe = 6 ft, 2 in = 8 ft, 3 in = 12 ft before a vent is required (typical code basis).

Water service sizing uses peak demand in gpm plus pressure loss through meter, backflow preventer, and developed length with fittings.

Developed length includes all horizontal and vertical pipe plus fitting equivalents; add 50% for fittings in preliminary sizing.

Pressure budget rule: minimum 8 psi (55 kPa) residual at the most remote fixture, with 15 psi typical for flushometer valves.

Plan layout order: locate fixtures and stacks, route building drain to sewer, then size vents and water mains from the most remote fixture back.

Velocity limits for sizing: 8 ft/s (2.4 m/s) in general distribution, 4-5 ft/s in basement or high-use runs to limit noise and erosion.

Copper type selection: Type L for typical domestic water, Type M only where permitted for above-ground; K for underground and buried service.

PEX expansion fittings require ASTM F1960; crimp/clamd rings use ASTM F1807; do not mix fitting systems across manufacturers.

Thermal expansion: closed systems with backflow preventers need an expansion tank sized to system volume and temperature rise.

Water pressure booster required when street pressure cannot deliver 8 psi residual at the topmost fixture after friction and elevation losses.

Static pressure gain: 1 psi per 2.31 ft of elevation drop (0.433 psi/ft); use for multi-story pressure checks.

Shock arrestors within 6 ft of quick-closing valves; water hammer arrestors sized by fixture units per ASSE 1010.

Minimum main size for a building water service is typically 3/4 in; flushometer systems need larger mains to control pressure drop.

Slope and size together govern capacity; a 4 in building drain at 1/4 in/ft carries about 216 fixture units (typical code table).

Vent stack sizing: a 1-1/2 in vent serves up to 8 fixture units; 2 in up to 24 FU; 3 in up to 84 FU (typical code basis).

Trap arm limits: developed length from trap weir to vent fitting must not exceed the trap arm length for that pipe size (e.g., 1-1/2 in = 6 ft).

Each trap needs a vent; common venting is allowed only when both fixtures are on the same floor and within the vertical distance limits.

Horizontal drain fittings: use long-turn (DWV) fittings for horizontal-to-horizontal changes; sanitary tees only for vertical-to-horizontal.

Cleanouts required at the base of each stack, at building drain intervals of 100 ft, and at changes of direction over 45 degrees.

Air admittance valves (AAV) per ASSE 1051/1050 may replace individual vents where the code adopts them; not for toilet fixture drains in most codes.

Backwater valve required on fixtures below the next upstream manhole cover elevation to prevent sewer backup.

Roof drain sizing uses 100-year, 1-hour rainfall intensity (in/hr) from local data; flow (gpm) = area (ft2) x intensity x 0.0104.

Vertical leader capacity exceeds horizontal storm drain capacity for the same diameter; size leaders and horizontal runs separately.

Primary roof drains plus secondary/scuppers: secondary system must handle the design storm if primary is blocked.

Sump pump and elevator pit drainage discharge to storm or approved receptor, never to sanitary sewer where prohibited.

Grease interceptors sized by fixture units or flow rate and retention time; typical 2-hour retention for restaurant waste.

Oil/sand separators required for garage and vehicle-wash drainage; sized by flow rate per manufacturer and code.

Indirect waste receptors require an air gap of at least twice the effective pipe opening, minimum 1 in.

Acid waste systems use corrosion-resistant pipe (glass, polypropylene, PVDF) with neutralization before discharge.

Water closet flush volumes: 1.28 gpf (4.8 L) standard; 1.6 gpf older; commercial flushometer valves typically 1.28-1.6 gpf.

Urinal flush volumes: 0.125-1.0 gpf; waterless urinals use a sealant cartridge and require special drain maintenance.

Fixture spacing: 15 in minimum from centerline of water closet to side wall or partition; 30 in minimum clear width.

Lavatory faucet flow limited to 1.5 gpm at 60 psi; showerheads 2.0 gpm; kitchen faucets 2.2 gpm (federal standards).

Air gap for fixture outlets: minimum 1 in or twice the effective opening, whichever is greater, above the flood-level rim.

Flood-level rim of a fixture is the point where water overflows; the critical level for backflow protection is measured from it.

Fixture carriers support water closets and wall-hung fixtures; floor-mounted carriers must resist 250 lb vertical and 250 lb horizontal loads.

Trap seal depth: 2-4 in (50-100 mm); deeper seals risk slow flow, shallower seals risk evaporation and sewer gas.

Storage tank sizing: first-hour rating (FHR) must meet peak-hour demand; FHR depends on tank volume and recovery rate.

Recovery rate (gph) = input BTU/hr x efficiency / (8.33 lb/gal x temperature rise x 1 BTU/lb-F).

Temperature and pressure relief valve (T&P) set at 210 F and 150 psi typical; discharge to a receptor within 6 in of the floor.

T&P discharge pipe must be full size, gravity-drained, and terminate with an air gap; no traps, no reducing fittings.

Thermal expansion tank required on closed systems; size to 2-5% of system volume or per manufacturer chart.

Combustion air: 50 ft3 per 1,000 BTU/hr input for confined spaces; two openings, one near top and one near bottom.

Recirculation systems: demand (on-demand) pumps save energy vs continuous; balance valve required to prevent short cycling.

Scald protection: tempering valve or thermostatic mixing valve at 120 F max for domestic hot water at fixtures.

Permit required before installing, altering, or replacing plumbing; minor repairs may be exempt per local amendment.

Inspection sequence: rough-in (before concealment), top-out, final; each must pass before the next stage.

ICC IPC and IAPMO UPC are the two dominant US model codes; local jurisdiction adopts one with amendments.

ASTM standards cover materials (e.g., ASTM D2665 PVC DWV, ASTM B88 copper tube); ASSE covers backflow and fixture fittings.

Code adoption: model code becomes law only when adopted by the authority having jurisdiction (AHJ).

Variance/alternate materials request must be submitted in writing to the AHJ with supporting test data or engineering.

Certificate of occupancy requires final plumbing inspection sign-off; no occupancy before final approval.

Contractor licensing and bonding are separate from code compliance; verify state and local license requirements.

Air gap is the highest protection (RPZ equivalent); minimum 1 in or twice the effective opening.

RPZ (reduced pressure zone) assembly: testable, protects against both backpressure and backsiphonage; check valve differential typically 5 psi.

Double check valve assembly (DCVA) protects against backpressure only; not for health hazards.

Pressure vacuum breaker (PVB) protects against backsiphonage only; cannot be used where backpressure exists and must be installed 12 in above highest downstream outlet.

Atmospheric vacuum breaker (AVB) is non-testable; used on hose bibbs and irrigation, must be 6 in above highest downstream point.

Annual testing of testable assemblies by a certified tester; records kept and submitted to the water authority.

Cross-connection survey identifies actual and potential connections; hazard classification (health vs non-health) drives assembly selection.

Thermal expansion control needed downstream of any backflow preventer because it creates a closed system.

DWV water test: fill system with water to 10 ft head above highest tested point, hold 15 minutes minimum before inspection.

DWV air test: 5 psi (35 kPa) for 15 minutes with gauge not dropping; use only where water test is impractical.

Water supply test: hydrostatic at 100 psi or working pressure plus 50 psi, whichever is greater, for at least 1 hour.

Final inspection verifies fixture operation, trap seals, vent termination height (6 in above roof, 10 ft from openings), and labeling.

Smoke test locates sewer gas leaks in DWV; blow smoke into system and observe for escape at joints.

Pressure drop diagnosis: if gauge drops, isolate sections with test plugs to localize the leak before cutting.

Trap seal loss causes: evaporation, capillary action, wind effect, momentum, backpressure; each has a different fix.

Water hammer diagnosis: check arrestor charge, valve closure speed, and pipe support spacing before adding devices.

Labor unit estimating: labor hours = quantity x labor unit (hr/unit); apply productivity factor for site conditions.

Material takeoff includes pipe, fittings, hangers, valves, and 5-10% waste allowance for cuts and breakage.

Critical path method (CPM) identifies the longest sequence of dependent tasks; plumbing rough-in usually precedes drywall and follows framing.

Change order must document scope, cost, and schedule impact; no work without written authorization.

Trench safety: protective system required at 5 ft depth or deeper; spoil pile at least 2 ft from edge.

Confined space entry requires atmospheric testing (O2, LEL, H2S, CO), attendant, and rescue plan.

Soldering and brazing require fire watch, hot work permit, and clearance from combustibles; PPE includes gloves and eye protection.

Ladder and scaffold safety: 4:1 ladder angle, 3-point contact, and fall protection above 6 ft in construction.