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
80
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
Carbon Monoxide AlarmvsCarbon Monoxide Detector
An alarm is a self-contained unit with sensor, controls, and notification appliance built in, while a detector only senses CO and transmits a signal to a separate alarm control unit.
International Residential Code, Section R202 Definitions (Carbon Monoxide Alarm and Carbon Monoxide Detector), PDF Pages 30-31Flow PressurevsStatic Pressure
Flow pressure is measured at an outlet while the faucet is wide open and flowing, whereas static pressure is measured when no water is moving in the system.
International Plumbing Code 2021, Page 2-4Mechanical JointvsSoldered / Solvent-Cemented Joint
A mechanical joint uses compression applied along the centerline and is NOT screwed, caulked, threaded, soldered, solvent cemented, brazed, welded, or heat fused, while the others are named chemical or thermal bonding methods.
International Plumbing Code 2021, Page 2-5Building Drain SizingvsVertical Stack Sizing
Horizontal stack offsets greater than 45° from vertical (below the lowest branch) must be sized as building drains using the building drain table, not the vertical stack table.
Ipc 2021, Section 710.1.1Standard Method (Indoor Combustion Air)vsMechanical Air Supply Method (Combustion Air)
The standard method requires 50 cu ft per 1,000 Btu/h of indoor volume, while the mechanical method requires outdoor air supplied at a rate of at least 0.35 cfm per 1,000 Btu/h.
International Residential Code, Section G2407.5.1Type B Gas Vent (termination height)vsResidential Chimney (termination height)
A Type B gas vent (≤12 in, ≥8 ft from wall) terminates per a roof-slope chart with a minimum 5 ft above the highest appliance draft hood, while a residential chimney must extend at least 3 ft above the roof penetration and 2 ft above any structure within 10 ft.
International Residential Code, Section G2427.6.4Sewage Ejector SumpvsSubsoil Drainage Sump Pit
Both require a minimum 18-inch diameter and 24-inch depth, but the sewage ejector sump (P3007.3.2) handles sanitary waste while the subsoil drainage sump (P3303.1.2) handles groundwater/stormwater.
International Residential Code, Chapter 30 Sanitary Drainage, P3007.3.2Developed LengthvsStraight-Line (Linear) Length
Developed length is measured along the centerline of pipe and fittings following the actual path of the pipe, whereas straight-line length is the direct point-to-point distance ignoring bends and fittings.
International Plumbing Code 2021, Page 2-3Permit-Required Plumbing WorkvsPermit-Exempt Plumbing Work
Replacing or rearranging valves, pipes, or fixtures requires a permit, while repairing leaks in existing valves or fixtures without replacement or rearrangement is exempt from permit requirements.
International Plumbing Code 2021, Page 1-4Horizontal Drainage Pipe < 3 inches diameter (slope)vsHorizontal Drainage Pipe ≥ 3 inches diameter (slope)
Pipes 3 inches and larger require a minimum slope of 1/8 inch per foot (1%), while smaller pipes are subject to steeper minimum slope requirements per the IRC drainage table.
International Residential Code, Chapter 30 Sanitary Drainage, P3005.3Underground Gas Piping (burial depth)vsWater Service Pipe (burial depth)
Underground gas piping must be buried at least 12 inches below grade, while water service pipe must be at least 12 inches deep AND at least 6 inches below the frost line.
International Residential Code, Section G2415.12Reduced Pressure Principle / Double Check Backflow PreventervsStandard Plumbing System Test
Backflow preventer assemblies must be tested at installation, after repairs, and annually every year thereafter, while a completed water-supply system is tested once at not less than working pressure (or 50 psi air) upon completion.
International Residential Code, Chapter 25 Plumbing Administration, P2503.8.2Key Terms
Mechanical Joint International Plumbing Code 2021, Page 2-5
Per IPC Section 202, a connection between pipes or fittings that uses compression along the centerline and is NOT screwed, caulked, threaded, soldered, solvent cemented, brazed, welded, or heat fused.
Flow Pressure International Plumbing Code 2021, Page 2-4
Per IPC Section 202, the pressure in the water supply pipe near a faucet or outlet while that outlet is wide open and flowing.
Drainage Fixture Unit (DFU) International Residential Code, Chapter 30 Sanitary Drainage, Table P3004.1
Per IRC Table P3004.1, a measure of the probable discharge load a fixture places on a drainage system, used to size DWV piping (e.g., a full-bath group with 1.6-gpf water closet = 5 DFU).
Developed Length International Plumbing Code 2021, Page 2-3
Per IPC Section 202, the length of a pipeline measured along the centerline of the pipe and fittings, following the actual routed path.
Effective Opening International Plumbing Code 2021, Page 2-3
Per IPC Section 202, the minimum cross-sectional area at the point of water supply discharge, expressed as the diameter of a circle of equivalent area; for faucets, measured at the smallest orifice in the fitting body or supply piping.
Backwater Valve International Residential Code, Chapter 30 Sanitary Drainage, P3008.1
Per IRC P3008.1, a valve installed in the building drain or horizontal branch to protect fixtures whose flood-level rims are below the elevation of the next upstream public sewer manhole cover.
Trap Liquid Seal International Residential Code, Chapter 32 Traps, P3201.2
Per IRC P3201.2, each fixture trap must maintain a liquid seal of not less than 2 inches and not more than 4 inches to prevent sewer gas entry.
Building Trap (Prohibition) International Residential Code, Chapter 32 Traps, P3201.4
Per IRC P3201.4, building traps are expressly prohibited in residential plumbing drainage systems.
NSF 61 Compliance International Residential Code, Chapter 26 General Plumbing Requirements, P2609.5
Per IRC P2609.5, all water service pipes, distribution pipes, fittings, valves, and faucets used to dispense water for human ingestion must be evaluated and listed to NSF 61 standards.
Shield Plate (Pipe Protection) International Residential Code, Chapter 26 General Plumbing Requirements, P2603.2.1
Per IRC P2603.2.1, a steel plate of not less than No. 16 gage (0.0575 inch) thickness required to protect non-cast-iron/non-galvanized piping that passes within 1¼ inches of the nearest edge of a stud or joist.
Static Pressure Loss per Foot of Elevation International Plumbing Code 2021, Page E-1 (Section E103.2.2, Item 2)
Per IPC Section E103.2.2, static pressure changes at 0.433 psi per foot of elevation difference between the water main and the fixture outlet.
Permit Application Abandonment International Plumbing Code 2021, Page 1-4
Per IPC Section 106.3.2, a plumbing permit application is deemed abandoned 180 days after filing if a permit has not been issued and the applicant has not pursued it in good faith.
Unvented Room Heater (Maximum Input) International Residential Code, Sections G2445.2 and G2445.3
Per IRC Section G2445.3, an unvented room heater shall not exceed an input rating of 40,000 Btu/h, and per G2445.2 may not serve as the sole source of comfort heating in a dwelling.
Clothes Dryer Exhaust Duct (Maximum Length) International Residential Code, Section G2439.7.4.1
Per IRC Section G2439.7.4.1, the maximum exhaust duct length for a domestic clothes dryer is 35 feet before reducing for fittings (e.g., a 4-inch radius mitered 90° elbow deducts 5 feet).
Combustion Air Opening (Horizontal Duct) International Residential Code, Section G2407.6.1
Per IRC Section G2407.6.1, where combustion air openings communicate outdoors through horizontal ducts, each opening must have a minimum free area of 1 square inch per 2,000 Btu/h of total appliance input.
Shower Liner Test International Residential Code, Page P2503.6 (Chapter 25 Plumbing Administration)
Per IRC P2503.6, a completed shower liner must be filled with potable water to at least 2 inches at the threshold and retained for not less than 15 minutes with no leakage.
Formulas to Know
Static Pressure Loss Due to Elevation
Pressure loss (psi) = Elevation difference (ft) × 0.433 psi/ftEquivalent Length with Fitting Allowance (50% Rule)
Equivalent length = Developed length × 1.5Equivalent Length with Fitting Allowance (1.2 Factor Method)
Max developed length = Actual pipe length (source to remote fixture) × 1.2Combustion Air Volume (Standard Method)
Required volume (cu ft) = Appliance input (Btu/h) ÷ 1,000 × 50Combustion Air Flow (Mechanical Method)
Required airflow (cfm) = Appliance input (Btu/h) ÷ 1,000 × 0.35Combustion Air Opening Free Area (Horizontal Duct)
Min free area (sq in) = Total appliance input (Btu/h) ÷ 2,000Clothes Dryer Duct Remaining Allowable Length After Fittings
Remaining length (ft) = 35 ft − Σ(equivalent lengths of all fittings)DFU Load — Multiple Bath Group
Total DFU = value from IRC Table P3004.1 based on number of bath groups (e.g., 2.5 baths = 9 DFU)