Exam Cheat Sheet · Quick Reference

Mississippi Residential Plumbing

Mississippi · PSI Services Contractor

Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.

Total questions

Passing score

70%

Exam time

240 min

Administered by

PSI Services Contractor

Format

Reference materials allowed

Mississippi State Portion 80 questions

General Plumbing Knowledge and Regulations 15 Q · 19%

Permit requirements, exemptions, and application proceduresInspection types and testing procedures for plumbing systemsCode official authority, duties, and enforcement powersViolations, stop work orders, and penaltiesKey plumbing terminology and definitionsProtection of pipes from physical damage, freezing, and corrosionTrenching, bedding, and backfilling requirements for buried pipingPiping support intervals and hanger requirements

Piping, Valves, and Controls 6 Q · 8%

Approved pipe materials for water service and water distribution systemsPipe joint methods by material type (solvent cement, heat fusion, mechanical, press-connect, solder/braze)Backflow prevention device types, applications, and applicable standardsValve requirements and locations (shutoff, full-open, pressure-reducing, water hammer arrestors)Water supply system design criteria (fixture units, flow rates, minimum pressure, pipe sizing)Potable water protection and cross-connection controlHydronic piping materials, joints, and shutoff valve requirementsNonpotable water system piping identification and labeling requirements

Fixtures and Equipment 4 Q · 5%

Minimum number of plumbing fixtures by occupancy typeFixture installation requirements and clearancesWater closet and urinal standards and flushing devicesShower compartments, receptors, and liner requirementsWater heater safety devices — temperature and pressure relief valvesWater heater installation, location, and access requirementsFixture-specific material and product standardsBackflow protection requirements for individual fixtures and appliances

Water Supply 4 Q · 5%

Backflow prevention devices and assemblies (types, standards, and applications)Potable water system design criteria (flow rates, pressures, and fixture supply sizing)Water supply and distribution pipe materials and approved standardsPipe joint and connection methods by material typeWater pressure requirements, pressure-reducing valves, and booster systemsWater hammer arrestors and thermal expansion controlValves (shutoff, full-open, service valve placement, and access requirements)Water piping system sizing methods (fixture units, developed length, friction loss)

Drain, Waste and Vent and Sewers 17 Q · 21%

Drainage fixture unit (DFU) values and system load calculationsSizing of horizontal drains, building drains, and building sewersSlope requirements for horizontal drainage pipingCleanout placement, sizing, and access requirementsPipe materials and joint methods for DWV systems (above-ground and underground)Vent system types and sizing (individual, common, wet, circuit, combination, air admittance valves)Trap requirements, prohibited trap types, and trap seal protectionSumps, sewage ejectors, and below-grade drainage systems

Isometric Analysis 9 Q · 11%

Reading and interpreting isometric/riser diagrams of DWV systemsAssigning drainage fixture unit (DFU) values to fixtures and fixture groupsAccumulating DFU loads from remote fixtures downstream to building drainSizing drain branches and stacks using fixture unit load tablesSizing building drain and building sewer based on slope and accumulated DFU loadDetermining vent pipe sizes and developed lengths from isometric layoutIdentifying required vent types and connections from system diagramSizing water supply piping segments using water supply fixture units and developed length

Safety 4 Q · 5%

Personal protective equipment (PPE) selection, use, and employer payment requirementsFire protection programs and portable fire extinguisher requirementsFlammable and combustible liquid storage and handlingExcavation cave-in protection and competent person inspectionsConfined space hazard identification and permit-required entry proceduresFirst aid, medical services, and emergency action plansToxic and hazardous substance exposure limits (PELs and TWAs)Asbestos identification, classification, and control methods

Specialty Applications 6 Q · 8%

Nonpotable water system design, storage tanks, and cross-contamination preventionOn-site nonpotable water reuse and graywater collection systemsRainwater collection, conveyance, filtration, and disinfection systemsSubsurface graywater soil absorption system sizing, percolation testing, and installationSolar thermal energy system installation, freeze protection, and relief valvesBoiler installation, safety controls, pressure relief, and expansion tanksFuel oil piping, storage tanks, and related fittingsIndirect waste piping, air gaps, air breaks, and special waste neutralization

Fuel Gas 5 Q · 6%

Gas piping materials, fittings, and joining methods (steel, copper, CSST, polyethylene)Gas pipe sizing methods and capacity tables (longest length, branch length, hybrid pressure)Pressure testing and leak checking of gas piping systemsCombustion air requirements (indoor, outdoor, and combination methods)Appliance location restrictions and clearances to combustiblesVenting system types and appliance categories (Type B, BW, L, direct-vent, Categories I–IV)Chimney and vent connector installation, sizing, and termination requirementsElectrical bonding requirements for gas piping and CSST

LP Gas 3 Q · 4%

LP gas pipe sizing using IFGC tables (undiluted propane, pressure drop, pipe length, material type)Two-stage regulator systems (first-stage high-pressure to second-stage low-pressure piping sizing)Allowable operating pressure limits for LP-gas piping systems inside buildingsApproved piping materials and fittings for LP-gas systems (metallic pipe, copper tubing, CSST, polyethylene)LP-gas plastic pipe limitations (underground-only use, maximum operating pressure of 30 psig, NFPA 58)Pressure testing and purging requirements for LP-gas piping installationsShutoff valves and appliance connectors for LP-gas systemsLP-gas motor vehicle fuel-dispensing facility requirements (location, equipment, safety devices)

Fuel Oil 2 Q · 2%

Fuel oil tank materials, standards, and listing requirements (UL 58, UL 80)Above-ground and indoor tank installation requirements and capacity limitsUnderground tank installation, clearances, and corrosion protectionOil piping and tubing materials, prohibited materials, and joining methodsFill piping and vent piping installation and termination requirementsOil pumps, shutoff valves, and maximum supply pressure requirementsOil-fired boiler and water heater listing and labeling standards (UL 726, UL 732)

Piping 5 Q · 6%

Water supply and distribution piping materials and applicable standards (copper, CPVC, PEX, PE-RT, PVC, galvanized steel)Sanitary drainage piping materials and applicable standards (ABS, PVC, cast iron, copper DWV, above-ground and underground)Pipe joints and connection methods by material type (solvent cementing, soldering/brazing, mechanical, heat fusion, press-connect, push-fit)Drainage system sizing using drainage fixture unit (DFU) values and pipe slope requirementsWater service pipe sizing, separation from building sewer, and minimum diameter requirementsCleanout requirements for drainage piping (location, spacing, size, access, prohibited uses)Pipe identification and labeling requirements for nonpotable water distribution pipingSubsoil drain and storm drainage piping materials and sump discharge piping requirements

Key Distinctions

Flow pressurevsStatic pressure (head)

Flow pressure is the pressure in the supply pipe near the faucet/outlet while it is wide open and flowing, whereas static pressure is a function of vertical elevation only, computed at 0.433 psi per foot of head.

IPC 2021 Page 2-4

Carbon monoxide alarmvsCarbon monoxide detector

An alarm combines sensor, control components and the notification appliance in one single- or multiple-station unit, while a detector has only an integral sensor and transmits an alarm signal to a connected alarm control unit.

IRC 2021 Section R202 Definitions (Carbon Monoxide Alarm and Carbon Monoxide Detector)

Vent stackvsStack vent

The vent stack is a separate vertical vent pipe that circulates air through the drainage system, connecting near the base of the soil stack and rejoining the stack vent above the highest fixture.

IPC 2021 Section 202

Stack vent sizing (Table 906.1)vsIndividual vent sizing (Section 906.2)

Stack vents are read off Table 906.1 using the stack size, DFU load and permitted developed length, while an individual vent is sized at half the fixture drain diameter with a 1-1/4 in minimum and one nominal size increase when the developed length exceeds 40 ft.

IPC 2021 Table 906.1

Horizontal stack offset sizingvsVertical stack sizing

Horizontal stack offsets (and, per IRC, an offset greater than 45 degrees from vertical below the lowest horizontal branch plus the stack below it) must be sized as building drains on accumulated DFU load rather than by vertical stack criteria.

IPC 2021 Section 710.1.1

Wet ventvsCircuit vent / combination waste-and-vent

A wet vent vents one or more fixtures while also carrying another fixture's discharge (classic single bathroom group), whereas circuit vents serve batteries of fixtures and combination waste-and-vent is a different, more restricted system.

Short sweep (or long sweep)vsSanitary tee

A short sweep is permitted for horizontal-to-horizontal changes of direction, while a sanitary tee is permitted only for horizontal-to-vertical connections (a standard quarter bend horizontal-to-horizontal is limited to specific small fixture drains).

IPC 2021 Table 706.3

Multiple-bath group DFU valuevsSum of individual fixture DFUs

Bath-group values (e.g., 5 DFU for a full-bath group with 1.6-gpf water closet; 9 DFU for 2.5 baths) are reduced values reflecting the probability of simultaneous use, instead of simply adding each fixture's value as is done for ordinary branches.

IRC 2021 For One- And Two-Fa, Table P3004.1

Trap-arm limit (Table 909.1)vsCrown-vent prohibition (Section 909.3)

Table 909.1 caps the maximum distance from trap weir to vent by trap size (e.g., 6 ft for 1-1/2 in, 8 ft for 2 in; not limited for self-siphoning water closets), while Section 909.3 sets the minimum, prohibiting a vent within two pipe diameters of the trap weir.

IPC 2021 Table 909.1

45-degree offset constant (1.414)vs22-1/2-degree offset constant (2.613)

For the same set, travel = set × 1.414 at 45 degrees (with run equal to the set), but travel = set × 2.613 at 22-1/2 degrees, giving a much longer diagonal.

Threaded pipe cut lengthvsSweat (solder) pipe cut length

Threaded cuts subtract both fitting takeoffs and add back both thread engagements, while sweat cuts simply deduct the printed allowance (1/2 in) for each fitting end.

Indoor combustion air — standard methodvsMechanical combustion air supply

The standard method requires a minimum indoor volume of 50 cubic feet per 1,000 Btu/h of appliance input, whereas an all-mechanical supply must deliver outdoor air at not less than 0.35 cfm per 1,000 Btu/h of total input of all appliances in the space.

IRC 2021 Section G2407.5.1

Building trapvsBackwater valve

Building traps are prohibited on residential drainage systems, while a backwater valve is required in the building drain, branch, or horizontal branch where fixture flood level rims are below the next upstream public-sewer manhole cover.

IRC 2021 Chapter 32 Traps, P3201.4

Key Terms

Flow pressure IPC 2021 Page 2-4

The pressure in the water supply pipe near the faucet or water outlet while that faucet or outlet is wide open and flowing.

Faucet IPC 2021 Page 2-4

A valve end of a water pipe through which water is drawn from or held within the pipe.

Effective opening IPC 2021 Page 2-3

The minimum cross-sectional area at the point of water supply discharge, expressed as the diameter of a circle (or equivalent-area circle), measured for faucets at the smallest orifice in the fitting body or supply piping.

Developed length IPC 2021 Page 2-3

The length of a pipeline measured along the centerline of the pipe and fittings, following the actual pipe path rather than a straight-line distance.

Branch interval IPC 2021 Definitions (Branch Interval)

A vertical measurement of distance of 8 feet or more in developed length between the connections of horizontal branches to a drainage stack; branches connecting less than 8 ft apart fall in the same interval.

Building drain IPC 2021 Definitions (Building Drain)

The lowest piping that collects discharge from all other drainage piping inside the house and extends 30 inches in developed length of pipe beyond the exterior walls to the building sewer.

Building trap IRC 2021 Chapter 32 Traps, P3201.4

A trap on the building drainage system that IRC P3201.4 prohibits in residential plumbing.

Backwater valve IRC 2021 Chapter 30 Sanitary Drainage, P3008.1

A valve installed in the building drain, a branch of the building drain, or a horizontal branch to protect fixtures whose flood level rims are below the manhole cover elevation of the next upstream public-sewer manhole.

Wet vent

A pipe that vents one or more fixtures while also carrying the discharge of another fixture, as in a single bathroom group.

Vent stack IPC 2021 Section 202

A separate vertical vent pipe installed to circulate air through the drainage system, connecting near the base of the soil stack and rejoining the stack vent above the highest fixture.

Trap liquid seal IRC 2021 Chapter 32 Traps, P3201.2

The water seal in each fixture trap, which must be not less than 2 inches and not more than 4 inches deep.

Subsoil drain IRC 2021 Chapter 33 Storm Drainage, P3302.1

Open-jointed, horizontally split, or perforated pipe not less than 4 inches in diameter used for subsoil drainage.

Ceiling height IRC 2021 Section R202 Definitions (Ceiling Height)

The clear vertical distance from the finished floor to the finished ceiling (finished surfaces, not framing).

Asbestos-containing material (ACM) 29 CFR 1926, §1926.1101(b)

Any material containing more than 1 percent asbestos by weight.

Exempt work (permits) IPC 2021 Page 1-4

Work not requiring a permit, including clearing stoppages, repairing leaks in pipes, valves or fixtures, and removal/reinstallation of water closets, provided no replacement or rearrangement of valves, pipes or fixtures is involved.

Abandoned permit application IPC 2021 Page 1-4

A permit application deemed abandoned 180 days after filing unless pursued in good faith or a permit has been issued, with extensions not exceeding 180 days each allowed by the code official.

Formulas to Know

Static pressure (or pressure loss) due to elevation head

psi = vertical height (ft) × 0.433 psi/ft; e.g., 14 ft × 0.433 = 6.06 psi (subtract when the fixture is above the source); 60 ft × 0.433 = 25.98 ≈ 26 psi

Total fall of a graded drain and resulting downstream invert

Fall = grade (in/ft) × run (ft); e.g., 1/8 in/ft × 32 ft = 4 in, 1/4 in/ft × 32 ft = 8 in. Downstream invert = upstream invert − total fall (convert 12 in = 1.00 ft); e.g., 100.00 ft − 1.00 ft = 99.00 ft; 101.00 − (11 in ÷ 12) = 100.08 ft

Grade expressed as percent slope% slope = (rise in inches per foot ÷ 12) × 100; e.g., (0.25 ÷ 12) × 100 = 2.08%

Simple offset travel and run

45°: travel = set × 1.414 and run = set × 1.000 (e.g., 16 × 1.414 = 22.62 ≈ 22-5/8 in; 20 × 1.414 = 28.28 ≈ 28-1/4 in, run = 20 in). 22-1/2°: travel = set × 2.613 (e.g., 10 × 2.613 = 26-1/8 in; 20 × 2.613 = 52-1/4 in)

Rolling offset true offset and travel

True offset = √(set² + roll²); e.g., √(12² + 9²) = 15.0 in. Travel = true offset × fitting constant: 45° → 15.0 × 1.414 = 21.2 in; 60° → 15.0 × 1.155 = 17.3 in

Cut length of threaded pipe

Cut = center-to-center − (takeoff × 2 fittings) + (thread engagement × 2 ends); e.g., 42 − (2 × 2-1/4) + (2 × 1/2) = 38-1/2 in; 36 − (2 × 2) + (2 × 1/2) = 33.00 in (deduct 4 in total for two 2-in takeoffs, add back 1 in total for two 1/2-in engagements)

Cut length of sweat (soldered) copper segments

Cut = center-to-center − (1/2 in per fitting end); e.g., 24 − (2 × 1/2) = 23.00 in and 18 − (2 × 1/2) = 17.00 in; combined total = 40.00 in

Minimum individual vent size

Base size = 1/2 × fixture drain diameter, but never less than 1-1/4 in (1-1/2 in drain → 0.75 → use 1-1/4 in; 2 in drain → 1 in → use 1-1/4 in; 3 in drain → 1.5 in → use 1-1/2 in); then increase one nominal size for the entire length if developed length exceeds 40 ft (e.g., 44 ft or 60 ft: 1-1/4 in → 1-1/2 in)

Total DFU load on a stack or branch (ordinary fixtures)

Add the DFU value of each connected branch/fixture; e.g., 5 + 5 + 2 + 2 = 14 DFU (a 3 in stack rated 48 DFU is adequate); 2 + 3 + 4 = 9 DFU; 4 + 1 + 2 = 7 DFU

Fitting/valve allowances in water pipe sizing

Segmented loss method: add 50% of the developed length (developed length × 1.5), e.g., 225 ft × 1.5 = 338 ft equivalent length. Section E104.1 method: maximum developed length = actual pipe length from source to most remote fixture × 1.2

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