MD Plumber cheat sheet

Water column: 1 psi = 2.31 ft of water head; conversely 1 ft of head = 0.433 psi. Use to convert static pressure to elevation and back.

Fixture unit basis: 1 water supply fixture unit (wsfu) = 1 gpm demand, roughly matched to a 3/4-inch flushometer or 1.6 gpf tank-type water closet under the standard Hunter method.

Slope: 1/4 inch per foot = 2 percent; 1/8 inch per foot = 1 percent; 1/16 inch per foot = 0.5 percent. Slope in percent = (rise / run) x 100.

Drainage fixture units (DFU) convert fixture counts to pipe size; a 1.6 gpf water closet is 3 DFU, a floor drain 2 DFU, a lavatory 1 DFU.

Developed length includes fittings; fitting allowance is added as equivalent length (e.g., 90-degree elbow ~ 2-3 pipe diameters of straight pipe, depending on table used).

Thermal expansion of water is about 4 percent by volume from 40 F to 140 F; closed systems need an expansion tank or relief provision.

Pressure test for DWV: water test 10 ft head minimum (about 4.3 psi) for 15 minutes, or air test at 5 psi for 15 minutes depending on the adopted code.

Flow velocity: keep domestic cold water below 8 fps and hot water below 5 fps to limit erosion and noise; 4-8 fps is the common design band.

Water closet limits (federal/EPAct baseline): 1.6 gallons per flush; urinal 1.0 gpf; showerhead 2.5 gpm at 80 psi; kitchen faucet 2.2 gpm; lavatory faucet 2.2 gpm (1.5 gpm for public lavatories in many codes).

Water heater temperature and safety: storage tank setpoint typically 120-140 F; scald protection required above 120 F at the fixture for bathing; T&P relief valve set at 150 psi or 210 F, whichever first.

T&P relief discharge must terminate by gravity, full size, within 6 inches of the floor or to a safe receptor, with no thread or cap on the end.

Fixture trap seal: 2 to 4 inches of water seal; trap arm length limited to the developed length permitted by the code (commonly 2 times the trap arm diameter in the drainage table).

Air gap is the only backflow protection that is not a device; minimum air gap is twice the effective opening of the supply pipe, never less than 1 inch.

Floor drains: trap primer or trap seal protection required where the trap is subject to evaporation; trap seal depth 2 to 4 inches.

Water closet rough-in: 12-inch rough-in places the drain centerline 12 inches from the finished wall; 10-inch and 14-inch rough-ins are the common alternates.

Backflow prevention: RPZ for high hazard, double check for low hazard, atmospheric vacuum breaker for hose bibbs and non-continuous use only.

Building drain vs building sewer: the building drain ends at the building wall (or 2 ft outside), and the building sewer begins there and runs to the public sewer or private disposal.

Vent stack and stack vent: a stack vent is the extension of a soil or waste stack above the highest fixture; a vent stack is a separate vertical vent for the drainage stack.

Wet vent rules: a wet vent may serve a bathroom group on the same floor when sized per table and the water closet is downstream of the vent connection, subject to local amendment.

Air admittance valves (AAVs) require at least one vent through the roof in the system and must be accessible; they do not replace a required vent terminal.

Water service sizing: use the fixture-unit method with the longest developed length and available pressure; subtract elevation (0.433 psi/ft) and meter/fixture losses.

Storm drainage: roof area (sq ft) x rainfall intensity (in/hr) / 96 = gpm; leader and horizontal storm drain size from that flow.

Backwater valve required on fixtures below the elevation of the next upstream manhole cover, where the code so requires.

Drainage grade: horizontal building drains 1/4 in/ft for 3-inch and smaller, 1/8 in/ft for 4-inch and larger, where the adopted code permits.

Maryland adopts the International Plumbing Code (IPC) as the Maryland Plumbing Code through COMAR 09.12.22 (Plumbing Code), with state amendments; local jurisdictions may adopt stricter amendments.

Licensing: the Maryland State Board of Plumbing administers master and journeyman plumber licenses under the Department of Labor; a master license is required to obtain a plumbing permit and to contract for plumbing work.

Apprenticeship: supervised apprentice hours (commonly 4 years / 7,500-8,000 hours) plus passing the journeyman exam are prerequisites for the journeyman license; the master exam follows journeyman experience.

Permits and inspections: a plumbing permit is required before installation; rough-in and final inspections are mandatory, and work must not be concealed before rough-in approval.

Continuing education: Maryland requires continuing education units for license renewal (commonly 10 hours per 2-year cycle for master/journeyman), with code-update hours specified by the Board.

Home improvement: plumbing contractors must hold an MHIC license in addition to the master plumber license when contracting with homeowners for home improvement work.

Sewage and water: on-site sewage disposal is regulated by the Maryland Department of the Environment (MDE) and the local health department; a percolation test and permit are required before installation.

Cross-connection control: Maryland requires backflow prevention and annual testing of testable assemblies by a certified backflow tester, with reports filed to the local water authority.