Exam Cheat Sheet · Quick Reference
Mississippi Residential HVAC
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
Insulation
3 Q · 4%
Duct insulation R-value requirements for unconditioned spaces (attics, crawl spaces, basements)Duct insulation materials — wrap, liner, duct board, and spray foam typesFlame spread and smoke-developed index requirements for duct coverings and linings (IMC Section 604)Vapor retarder requirements for externally insulated cooling ductsDuct insulation identification and labeling requirementsImpact of duct insulation R-value on heating and cooling load calculations (Manual J duct load factors)Internal duct liner installation — interruption at fire dampers and metal nosings at exposed edgesWeatherproof barriers for exterior duct insulation
Hangars and Supports
3 Q · 4%
Hanger spacing requirements for rectangular, round, and flat oval ductsUpper attachment methods to building structures (concrete inserts, powder-actuated fasteners, beam clamps, welded studs)Hanger and strap material selection and minimum sizes per duct perimeterTrapeze hanger design and load calculationsRiser duct support methods and maximum support intervalsLower attachment devices connecting hangers to duct sectionsSupport requirements near elbows and branch intersectionsIMC 2021 duct support compliance and piping support spacing requirements
Sound, Vibration & Seismic Control
1 Q · 1%
Vibration isolation requirements for HVAC equipment and supplemental restraint (IMC 301.13)Duct sheet vibration and threshold velocity criteria for rectangular ductsNoise generation and transmission in duct systems (acoustic lining, duct liner installation)Seismic resistance requirements for mechanical system supports and anchorage (IMC 301.18)Oil canning and cross-breaking of sheet metal panels to reduce rumble and vibrationFlexible connections at fans to isolate vibration from ductworkDuct air velocity limits to prevent excessive noise in supply and return ductsWind resistance requirements for exposed mechanical equipment and appliances (IMC 301.15)
Heating and Cooling Principles
6 Q · 8%
Heat transfer methods: conduction, convection, and radiationSensible heat and latent heat in HVAC applicationsRefrigeration cycle fundamentals: compression, condensing, metering, and evaporationHeating and cooling load calculation principles (Manual J)Indoor and outdoor design temperatures for load calculationsThermal resistance and transmittance values (R-value, U-value, K-value, C-value)Heat pump heating and cooling modes and efficiency ratings (COP, SEER, HSPF)Forced-air and hydronic heating system fundamentals
Refrigerants
4 Q · 5%
Refrigerant classification and types (CFC, HCFC, HFC, HFO, HC, inorganic)Environmental impact: ozone depletion potential (ODP) and global warming potential (GWP)EPA Section 608 regulations and technician certification requirementsRefrigerant identification: ASHRAE numbering system and cylinder color codesRefrigerant safety classifications: toxicity and flammability (ASHRAE Standard 34)Pressure-temperature relationships and P/T chart usageRefrigerant phaseout schedules and approved replacement refrigerantsRefrigeration lubricant types and compatibility with refrigerants
Load Calculations
6 Q · 8%
Indoor and outdoor design conditions (HTD, CTD, design temperatures)Thermal resistance and transmission values (R-value, U-value, K-value, C-value)Heat transfer multipliers (HTM) for fenestration and opaque panelsFenestration loads (windows, glass doors, skylights — heating and cooling)Opaque panel loads (walls, ceilings, floors, doors — heating and cooling)Infiltration load estimation methods (ACH table, component leakage area, blower door)Duct load procedures (conduction, leakage, load factors for unconditioned spaces)Internal loads (occupants, appliances) and ventilation loads
Testing, Adjusting and Balancing
1 Q · 1%
Airflow measurement instruments and techniques (anemometers, pitot tubes, manometers, flow hoods)Duct system balancing methods (damper adjustment, airflow rate calculation per room)Blower door testing and building envelope airtightness (ACH50, cfm50)Duct leakage testing using duct blaster (cfm25, maximum allowable leakage)Psychrometric properties and use of psychrometric charts in system assessmentAir velocity calculations (velocity pressure formula, traverse point measurement patterns)Duct system noise diagnosis and correctionIMC requirements for balancing air distribution and ventilation systems (Section 608)
Controls
4 Q · 5%
Thermostat types and sensing elements (bimetal, thermistor, mercury switch, millivolt)Heat and cooling anticipatorsLow-voltage, line-voltage, and millivolt thermostat operationProgrammable and digital thermostat installation and programmingOil burner primary controls and flame detection (cad cell, stack-mounted)Oil burner limit controls (low water cutoff, steam pressure, aquastat)Control circuit wiring for heating systems (steam, hot water, warm air)Motor control devices (pressure controls, relays, contactors, and motor protection)
A/C and Heat Pump Equipment
6 Q · 8%
Compressor types and configurations (reciprocating, rotary, scroll, hermetic, semi-hermetic)Metering devices for A/C and heat pump systems (capillary tube, TXV, fixed-orifice/piston, EEV)Heat pump reversing valve operation and refrigerant flow directionHeat pump types (air-source, ground-source, water-source) and system componentsRefrigerant flow components (filter-driers, sight glasses, check valves, solenoid valves, accumulators)Ductless and packaged A/C equipment (room air conditioners, PTACs, ductless split systems, multizone VRF)Residential central split-system A/C components, installation, and serviceIMC refrigeration system classification, refrigerant quantity limits, and machinery room requirements
Furnaces and Heaters
5 Q · 6%
Gas furnace ignition systems (standing pilot, intermittent pilot, direct-spark, hot-surface)Oil-fired furnace components and operation (fuel units, burner nozzles, electrodes, primary control units)Electric resistance heating systems (electric furnaces, duct heaters, baseboard units, radiant heat)Combustion efficiency testing (CO2, stack temperature, draft, and smoke tests)Furnace types and configurations (upflow, downflow, horizontal, two-stage, modulating)Gas furnace safety controls (high-limit switch, rollout switch, pressure switch, flame rectification)Fuel oil delivery systems and storage tanks (one-pipe, two-pipe, fuel line components, IMC/NFPA 31 requirements)IMC requirements for specific heating appliances (forced-air furnaces, unit heaters, wall furnaces, floor furnaces, infrared heaters)
Chimneys, Flues and Vents
3 Q · 4%
Appliance venting categories (Category I, II, III, IV) and vent type selectionVent and chimney sizing methods using code tables (single and multiple appliances)Vent connector requirements — materials, size, slope, clearances, and length limitsChimney termination height and location requirementsMasonry chimney construction, lining materials, and cleanout requirementsFactory-built chimney listing, installation, and support requirementsDraft hoods, draft controls, and mechanical draft system requirementsCombustion process fundamentals and flue gas products (CO2, CO, excess air)
Combustion Air
3 Q · 4%
Primary air, secondary air, and excess air requirements for complete combustionIndoor combustion air volume requirements (standard method and known air-infiltration-rate method)Outdoor combustion air supply methods (two-permanent-openings and one-permanent-opening methods)Combustion air opening sizing, placement, and minimum dimensionsCombustion air duct construction, materials, and installation requirementsMechanical combustion air supply systems and appliance interlock requirementsLouvers, grilles, and screens: free area calculations and motorized damper interlockingCombination indoor and outdoor combustion air provisions
Ducts
14 Q · 18%
Rectangular duct construction: gage selection, reinforcement schedules, and pressure classificationRound and oval duct construction: wall thickness, longitudinal and spiral seam requirements, and transverse jointsDuct sealing requirements, leakage classes, and sealant/tape application methodsDuct hangers and supports: spacing, hanger types, trapeze selection, and attachment methodsDuct system types and supply/return air distribution layoutsFlexible duct installation standards, flexible connectors, and length limitationsDuct insulation requirements and duct load calculations (conduction and leakage losses)Duct accessories: volume dampers, turning vanes, access doors, registers, grilles, and diffusers
Ventilation and Exhausts
3 Q · 4%
Exhaust discharge location and minimum separation distancesClothes dryer exhaust system requirements and duct length limitsCommercial kitchen exhaust hoods (Type I and Type II) and airflow ratesMinimum mechanical ventilation rates by occupancy typeNatural ventilation requirements and openable area calculationsIndoor air quality: pollutants, filtration methods, and MERV ratingsEnergy recovery ventilators (ERVs) and heat recovery ventilators (HRVs)Airflow measurement, system balancing, and duct testing
Safety
2 Q · 2%
Personal protective equipment (PPE) selection and useFall protection systems (guardrail, safety net, personal fall arrest)Ladder and stairway safety requirementsFire protection and prevention on construction sitesHazardous and toxic substances exposure limitsConfined space entry procedures and permit requirementsLockout/tagout (LOTO) procedures for electrical and other energy sourcesScaffold safety requirements and load capacity
Fuel Gas
5 Q · 6%
Gas piping materials and fittings (metallic pipe, copper tubing, CSST, polyethylene)Gas pipe sizing methods (longest length, branch length, hybrid pressure) and sizing tablesAllowable pressure drop and maximum operating pressure for piping systemsCSST bonding and electrical grounding requirementsCombustion air requirements (indoor, outdoor, and combination methods)Fuel gas appliance installation requirements (clearances, prohibited locations, access)Combustion principles (stoichiometric combustion, flammability limits, primary and secondary air)Safety inspection procedures for existing gas appliance installations
LP Gas
4 Q · 5%
LP gas piping materials and allowable pipe typesLP gas piping sizing methods and capacity tablesLP gas pressure requirements and regulators (single-stage and two-stage)LP gas piping installation requirements (burial depth, support intervals, protection)LP gas piping pressure testing and leak detection proceduresLP gas combustion properties and burner operationCSST bonding and grounding requirements for LP gas systemsLP gas motor vehicle fuel-dispensing facility requirements
Fuel Oil
2 Q · 2%
Fuel oil grades, properties, and classifications (viscosity, flash point, pour point, heat content)Fuel oil storage tank types, sizing, and installation requirements (gravity feed and two-pipe systems)Fuel oil piping materials, joints, and connections per IMC Chapter 13Fuel oil pump types, operation, and testing procedures (pressure, cutoff, and vacuum tests)Oil burner nozzle selection, spray patterns, angles, and flow ratesFuel oil tank fill, vent, gauge, and safety valve requirementsOil leak detection, odor complaints, and buried tank pressure testingFuel delivery system troubleshooting (no oil, pump replacement, filter service)
Piping
5 Q · 6%
Gas piping materials and allowable standards (steel, copper, CSST, polyethylene)Gas pipe sizing methods and sizing tables (longest length, branch length, hybrid pressure methods)Gas piping pressure testing, leak detection, and purging proceduresGas piping installation requirements (support, protection, burial depth, prohibited locations, bonding of CSST)Shutoff valves and pressure regulators for gas piping systemsHydronic piping materials, fittings, and joint types (copper, PEX, CPVC, steel)Fuel oil piping materials, installation, and system components (supply, return, vent, fill lines)Refrigerant tubing types, cutting, bending, and connection methods (flaring, brazing, soldering, swaging)
Key Distinctions
Pictorial wiring diagramvsLadder diagram
A pictorial diagram shows all connections plus the approximate physical location of devices in the unit (and may show wire colors), while a ladder diagram shows the order of component operation on horizontal rungs between two vertical power lines.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 18 - Electrical Troubleshooting Fundamentals, Page 369 (Section 18.2.2) (20th ed.: Chapter 16, Section 16.1.1)PTC thermistor when coolvsPTC thermistor at set point
Cool, the PTC has a low resistance of 3 Ω to 12 Ω so start current takes that path instead of the parallel run capacitor; once heated to its set point its resistance rises to 10 kΩ–20 kΩ, forcing current through the run capacitor.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 346 (Section 17.5) (20th ed.: Chapter 16, Section 16.3.5 — Positive Temperature Coefficient Relays)Solid-state relay (SSR)vsElectromagnetic relay
An SSR switches circuits electronically with transistors, SCRs, or triacs and has no physical movement of mechanical parts, whereas an electromagnetic relay uses mechanical contacts; SSRs are typically used to start single-phase motors.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 345 ("Solid-State Relays") (20th ed.: Chapter 16, Section 16.3.5 — Solid-State Relays)ACR tubing sizingvsCopper water tubing sizing
ACR tubing is designated by its actual outside diameter, while copper water tubing nominal size equals the outside diameter minus 1/8″.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 5 - Working with Tubing and Piping, Page 71 (Section 5.1.1) (20th ed.: Chapter 8, Section 8.1.1)Galvanized steel pipevsBlack steel pipe
Galvanized pipe is treated with a zinc anticorrosion material and is used primarily in water systems to prevent rust, while black pipe is usually less expensive and is used for gas lines and applications not carrying water.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 5 - Working with Tubing and Piping, Page 74 (Section 5.3) (20th ed.: Chapter 8, Section 8.2.3)Building-related illness (BRI)vsSick building syndrome (SBS)
BRI is a specifically diagnosable illness caused by airborne agents whose symptoms do not disappear when the occupant leaves, while SBS has no specific cause or identifiable illness and its symptoms disappear when occupants leave the building.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 29 - Air Quality, Page 647 (20th ed.: Page 730)K-value (thermal conductivity)vsC-value (thermal conductance)
K-value is based on a standardized one-inch thickness of material (Btu·in/hr·ft²·°F), while C-value is based on the material's actual measured thickness.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 32 - Heating and Cooling Loads, Page 717 (20th ed.: Page 986)Subcooling charging methodvsSuperheat charging method
The subcooling method is generally used to check charge on systems with thermostatic expansion valves, while the superheat method is used on systems with fixed orifice metering devices such as capillary tubes.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 12 - Working with Refrigerants, Page 221 (20th ed.: Page 236)Pilot-operated reversing valvevsDirect-acting reversing valve
A pilot-operated valve uses a solenoid pilot valve and capillary tubes to harness the pressure difference between suction and discharge lines to shift the piston, while a direct-acting valve shifts by direct mechanical action of the solenoid plunger and is used in smaller systems.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 36 - Air-Source Heat Pumps, Page 863 (20th ed.: Pages 1094-1095)Time-terminated defrostvsTemperature-terminated defrost
Pure time-based defrost runs a fixed duration regardless of coil condition, while temperature-terminated defrost uses a thermostat or thermistor on the coil to end defrost when the coil reaches a set temperature; time-initiated/temperature-terminated is the most common commercial method.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 44 - Commercial Evaporators, Condensers, and Other Heat Exchangers, Page 1054 (20th ed.: Chapter 21, Section 21.1.9)In-line ammeter connectionvsVoltmeter/ohmmeter connection
Unlike voltmeters and ohmmeters, an in-line ammeter is connected in series (in-line) with the circuit or load, and on dc the polarity must match — black lead to the negative side, red lead to the positive side — before energizing.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 18 - Electrical Troubleshooting Fundamentals, Page 362 ("In-Line Ammeters") (20th ed.: Chapter 17, Section 17.1.3 — In-Line Ammeters)Hot-surface igniter (glow coil)vsFlame rod
In an HSI system the glow coil only ignites the gas and cannot sense flame; a separate flame rod proves flame by rectification, and if it is dirty or oxidized the control closes the gas valve seconds after ignition.
Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 33 - Gas-Fired Heating Systems, Page 765 (20th ed.: Pages 1126-1128 (Sections 41.5.4 and 41.6.1))Key Terms
Competent person (29 CFR 1926.32(f)) OSHA 1926 CFR 29, Page 31
One who is capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them (no specific degree, experience, or certificate required).
Bonding jumper (IFGC 202) IFGC 2018 Section 202 Definitions
A conductor installed to electrically connect metallic gas piping to the grounding electrode system.
EHD (Equivalent Hydraulic Diameter) IFGC 2018 Table 402.4(15), Note 2
In CSST sizing tables, a measure of relative hydraulic efficiency between tubing sizes — the greater the EHD value, the greater the gas capacity of the tubing.
Longest length method (IFGC 402.4.1) IFGC 2018 Section 402.4.1
A sizing method in which the size of each section of gas piping is determined using the longest length of piping from the point of delivery to the most remote outlet along with the load of that section.
Velocity pressure Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 28 - Air Movement and Measurement, Page 630 (20th ed.: Page 710)
The difference between total air pressure and static air pressure (total pressure = static pressure + velocity pressure), measured with a pitot tube whose inner tube senses total pressure and whose outer side holes sense static pressure.
Distributor Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 45 - Commercial Metering Devices and Valves, Page 1088 (Section 45.1.4) (20th ed.: Pages 490-491)
A device at the outlet of a metering device that splits refrigerant flow into several shorter parallel evaporator circuits, reducing pressure drop across the evaporator and giving more consistent coil temperature.
Draft Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 34 - Oil-Fired Heating Systems, Page 796 (20th ed.: Page 1155)
The movement of flue gas; a draft test measures flue air pressure in inches of water column (in. WC) to indicate how quickly flue gases pass through the heat exchanger.
Overfiring Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 34 - Oil-Fired Heating Systems, Page 795 (Section 34.3.2) (20th ed.: Page 1154)
A condition in which a heating system creates too much heat — often from installing a burner nozzle of higher capacity than the original — so excess heat escapes up the flue and stack temperature runs high.
Sequencer Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 35 - Electric Heating Systems, Page 834 (20th ed.: Pages 1196 and 1205)
A device that opens and closes its contacts on a time delay (typically about 30 seconds apart) to energize electric furnace heating elements one at a time, minimizing initial current draw.
Category IV furnace Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 33 - Gas-Fired Heating Systems, Page 776 (20th ed.: Page 1134)
A positive-pressure venting, condensing furnace whose flue gas temperature is below 140°F (60°C) — below its dew point — using a secondary heat exchanger and PVC vent piping.
K-value (thermal conductivity) Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 32 - Heating and Cooling Loads, Page 717 (20th ed.: Page 986)
The amount of heat that will pass through one square foot of a material one inch thick in one hour with a 1°F temperature difference between its two sides (Btu·in/hr·ft²·°F).
Wall Area Ratio (WAR) Manual J, Section 4, Page 4-6
The gross exposed wall area for a room divided by the gross exposed wall area for the entire block load; used to apportion block infiltration load and infiltration CFM to each room.
Total effective length (TEL) Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 30 - Air Distribution, Page 687 (20th ed.: Page 772)
The greatest effective length of a supply duct run added to the greatest effective length of a return duct run, representing the straight-duct length offering the same resistance as the most restrictive supply and return runs combined.
Differential Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 325 (Section 17.2.2) (20th ed.: Chapter 16, Section 16.2.2)
The difference between a control's cut-out and cut-in values, representing the temperature swing during which the system cycles.
PTC relay Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 17 - Electrical Control Systems, Page 346 (Section 17.5) (20th ed.: Chapter 16, Section 16.3.5 — Positive Temperature Coefficient Relays)
A positive temperature coefficient thermistor wired in parallel with the run capacitor of a PSC motor; it has 3–12 Ω when cool and rises to 10 kΩ–20 kΩ when heated, shifting current to the run capacitor after start-up.
Crankcase heater Modern Refrigeration and Air Conditioning (22nd ed.), Chapter 43 - Commercial Compressors, Page 1045 (Section 43.1) (20th ed.: Page 467)
An electric heating element on or in a compressor that warms the compressor during the Off cycle to prevent refrigerant from condensing into liquid in the crankcase, avoiding liquid slugging or a flooded start.
Formulas to Know
Air velocity from velocity pressure (pitot tube and manometer)
V (ft/min) = 4005 × √Pv, where Pv is velocity pressure in inches of water; e.g., 4005 × √0.25 = 2,002.5 ≈ 2,003 ft/minAdditional refrigerant charge for a long line set
Additional feet = total line set length − 15 ft covered by factory charge; Additional charge = additional feet × 0.6 oz/ft; lb = oz ÷ 16 (e.g., 65 − 15 = 50 ft; 50 × 0.6 = 30.0 oz = 1.875 ≈ 1.9 lb)Total equivalent length and friction loss of a duct run
Total equivalent length = sum of straight lengths + (number of elbows × elbow equivalent length); e.g., 28 + 22 + 15 + (2 × 25) = 115 ft. Friction loss = (total equivalent length ÷ 100) × friction rate = (115/100) × 0.10 = 0.115 in. WCDesign friction rate and total effective length (residential duct sizing)
Friction Rate = (ASP ÷ TEL) × 100, e.g., (0.20 in. WC ÷ 250 ft) × 100 = 0.08 in. WC per 100 ft; TEL = longest supply effective length + longest return effective length (180 + 120 = 300 ft)Manual J surface loads: HTM, area loads, and net wall area
HTM = U × HTD (e.g., 0.07 × 75 = 5.25 Btuh/sq ft); Load = area × HTM (net wall 136 sq ft × 3.50 = 476 Btuh; ceiling 140 sq ft × 1.50 = 210 Btuh; door 20 sq ft × 35.00 = 700 Btuh); Net exposed wall = (wall length × height) − window area − door area (24 × 9 = 216 − 60 − 20 = 136 sq ft); Net wall area for a building = (perimeter × ceiling height) − (window + door area) (180 × 8 = 1,440 − 122 = 1,318 ft²); Room total = wall + glass + door + ceiling + infiltration (770 + 1,155 + 700 + 470 + 1,725 = 4,820 Btuh)Infiltration airflow and infiltration heating load (sensible only for heating)
Infiltration CFM = (ACH × above-grade volume of heated space) ÷ 60; ACH = (cfm × 60 min) ÷ room volume in ft³; Heating infiltration load = 1.1 × ACF × CFM × HTD (1.1 × 1.00 × 22.4 × 70 = 1,725 Btuh); Qs = 0.018 × CFH × TD — for heating loads only sensible loss is counted (cooling loads count both sensible and latent); Room infiltration load = block infiltration load × WARSlab-on-grade added heat loss (0°F outdoor design temperature)
Slab heat loss = building perimeter (linear ft) × 18 Btu/hr per foot, added to the above-ground heat losses (based on perimeter length, not slab area)Btu/hr to kilowatts for electric heat sizing
kW = Btu/hr ÷ 3,413 (50,000 ÷ 3,413 = 14.65 kW minimum)Coefficient of performance from a pressure-enthalpy diagram
COP = refrigeration effect ÷ heat of compression = (compressor-in enthalpy − evaporator-in enthalpy) ÷ (compressor-out − compressor-in) = (179 − 116) ÷ (198 − 179) = 63 ÷ 19 = 3.32:1Mixed-air temperature, outdoor-air percentage, and airflow balance
T_mix = (Return CFM × Return Temp + Outdoor CFM × Outdoor Temp) ÷ Total CFM = (3,000 × 60 + 1,000 × 92) ÷ 4,000 = 68.0 °F; OA% = Outdoor CFM ÷ Total CFM = 1,000/4,000 = 25%; Mixed CFM must equal the sum of entering streams (3,000 + 1,000 = 4,000 CFM)