Exam Cheat Sheet · Quick Reference

South Carolina - Air Conditioning

South Carolina  ·  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

South Carolina State Portion 80 questions

General Piping 1 Q · 1%
Gas piping system sizing methods and sizing tables (longest length, branch length, hybrid pressure)Approved piping and tubing materials for fuel gas systems (steel, copper, CSST, polyethylene, aluminum)Piping joints, fittings, and connection methods (threaded, brazed, welded, press-connect, flared)Pressure testing, leak detection, and purging of gas piping systemsPiping support intervals and protection against physical damageShutoff valves and pressure regulators in gas piping systemsHydronic piping materials, joints, and testing requirementsRefrigerant tubing types, cutting, bending, flaring, brazing, and soldering proceduresGas Piping Installations
General Tubing 1 Q · 1%
ACR copper tubing types and specifications (soft vs. hard-drawn, Type K and L wall thickness, sizing by OD)Cutting tubing procedures and tools (tubing cutter, hacksaw blade selection, squaring, reaming, and deburring)Bending tubing methods and minimum bend radius (bending springs, lever-type benders, kinking prevention)Flared connections and fittings (single and double flares, flaring procedure, SAE vs. JIC angles, flare nut sizing)Soldering and brazing procedures (flame types, filler metals, flux application, capillary action, purging with nitrogen)Swaged connections (swaging tools, overlap length, preparation for soldered or brazed joints)Non-refrigerant tubing and pipe types (copper water tubing, ABS/PVC/CPVC plastic pipe, steel pipe, joining methods)Specialized tube couplings and dissimilar metal connections (mechanical and compression fittings for aluminum-to-copper joints)Working with Tubing and Piping
Pipe Assembly 1 Q · 1%
Types of refrigerant and non-refrigerant tubing and pipe (ACR copper, plastic, steel)Cutting, reaming, and bending tubing techniques and toolsFlared connections: single and double flare procedures and fittingsSoldering and brazing procedures, equipment, and filler materialsSwaged connections and specialized tube couplingsGas piping materials, joints, and fittings per SC Fuel Gas CodeGas pipe sizing methods, pressure drop, and allowable operating pressureHydronic piping materials, joint types, and installation requirements per SC Mechanical CodeGas Piping Installations
Piping Systems 4 Q · 5%
Gas piping sizing methods and pressure drop calculationsApproved piping and tubing materials for gas, refrigerant, and hydronic systemsPiping joints and connection types (brazed, soldered, flared, threaded, mechanical)Refrigerant line components (filter-driers, sight glasses, liquid receivers, check valves, solenoid valves)Hydronic piping system designs and installation requirementsFuel oil piping materials, joints, and installation requirementsPiping system testing and pressure requirementsTubing cutting, bending, and fabrication techniquesGas Piping InstallationsHydronic Heating FundamentalsRefrigerant Flow ComponentsWorking with Tubing and Piping
Drain Piping 1 Q · 1%
Condensate drain pan requirements and placement relative to cooling coilsCondensation prevention on duct exteriorsSlope requirements for drainage in underground duct installationsPlastic piping and tubing in plenums (flame spread and smoke-developed index requirements)Plumbing and mechanical products in plenums listing and labeling requirementsDuct Systems
Valves 1 Q · 1%
Refrigerant flow control valves: shutoff, check, and solenoid valve types and operationService valve positions and procedures: back seated, front seated, mid-position, and cracked openPressure-regulating valves: crankcase pressure regulators (CPRs) and evaporator pressure regulators (EPRs)Relief valves and safety pressure devices for refrigerant systems and cylindersMetering devices as valves: thermostatic expansion valves (TXVs), automatic expansion valves (AXVs), and electronic expansion valves (EEVs)Hydronic system valves: mixing valves, balancing valves, pressure-reducing valves, flow-control valves, backflow preventers, and zone valvesShutoff valve placement requirements in hydronic piping systems per SC Mechanical CodeGas piping valve and regulator requirements per SC Fuel Gas CodeGas Piping Installations
Piping Specialties 1 Q · 1%
Refrigerant flow control valves (shutoff, check, solenoid, and service valves)Filter-driers and sight glasses/moisture indicators for refrigerant systemsPressure-regulating valves (crankcase pressure regulators, evaporator pressure regulators, relief valves)Gas piping materials, fittings, and joint types (SC Fuel Gas Code Chapter 4)Gas piping sizing methods and pressure drop requirementsGas piping shutoff valves and appliance connectionsHydronic piping materials, fittings, and joint types (SC Mechanical Code Chapter 12)Tubing cutting, bending, flaring, brazing, and swaging techniquesGas Piping Installations
Pumps 2 Q · 2%
Circulating pump types and components (wet-rotor centrifugal pumps, impellers)Pump placement relative to expansion tankCavitation causes and effects on circulating pumpsWater circulation troubleshooting (air-bound systems, bleeding and purging procedures)Pump operation sequences in hydronic system controlsHydronic system pressure testing requirements (100 psi minimum, 15-minute duration)Shutoff valve requirements at pumps and system equipment per SC Mechanical CodeHydronic Heating Fundamentals
Piping Insulation 1 Q · 1%
Insulation flame spread and smoke-developed index requirements (ASTM E84/UL 723)Required insulation thickness per International Energy Conservation CodeInsulation characteristics for air plenum installationsHeat loss factors for bare vs. insulated hot water and steam piping (Btuh/foot)Heat gain factors for chilled water piping insulation by pipe size and R-valueEffect of pipe location (conditioned vs. unconditioned space) on piping loadPipe heat loss calculation using temperature difference, pipe length, and insulation factorRadiant floor system insulation and thermal break requirements
Hangers and Supports (General) 1 Q · 1%
Duct support requirements per SMACNA standardsHanger and support spacing intervals for hydronic piping per Section 305Flexible duct and factory-made duct support per manufacturer instructionsPipe support requirements for ground-source heat pump loop systemsProtection of supported ducts from mechanical damage and weatherStructural integrity requirements for duct bracing and reinforcementDuct Systems
Mechanical Sound, Vibration, and Seismic Control 1 Q · 1%
Vibration isolator selection and installation for HVAC equipmentFlexible duct and pipe connections for vibration attenuationSeismic restraint requirements for mechanical equipmentSound transmission control and STC ratings in HVAC systemsNoise criteria (NC) levels for occupied spacesAcoustic duct lining and sound attenuator applicationsEquipment placement and mounting to minimize structure-borne noiseGeneral Regulations
Water Treatment for Mechanical Systems 1 Q · 1%
Glycol additives and freeze protection (propylene vs. ethylene glycol, mixture ratios)Scale formation and impurity limits in boiler waterCorrosion causes and prevention (chemical scavengers, corrosion inhibitors, deaeration)Water pH requirements and embrittlement preventionInitial system preparation and boiling-out procedures (trisodium phosphate treatment)Air removal and its role in corrosion control (dissolved, free, and entrained air)Transfer fluid compatibility and flash point requirements per SC Mechanical CodeChemical compatibility of antifreeze with piping materials in ground-source heat pump systemsHydronic Heating Fundamentals
Heating and Cooling Principles 2 Q · 2%
Heat transfer modes (conduction, convection, radiation)Sensible heat and latent heat distinctionsThermal resistance values (R-value, U-value, K-value, C-value)Indoor and outdoor design temperatures (HTD and CTD)Heating loads: envelope conduction, infiltration, and ventilation sourcesCooling loads: solar gain, internal gains, and fenestration componentsHeat pump operating principles (heating mode and cooling mode)Compression refrigeration cycle fundamentalsHeating and Cooling Loads
Refrigerants 1 Q · 1%
Refrigerant classification (CFC, HCFC, HFC, HFO, HC, inorganic)Ozone depletion potential (ODP) and global warming potential (GWP)Refrigerant numbering system and cylinder color codesRefrigerant toxicity and flammability classifications (ASHRAE Standard 34 safety groups)Pressure-temperature (P/T) charts and pressure-enthalpy diagramsRefrigerant phaseout schedules and EPA Section 608 requirementsRefrigerant recovery, recycling, and reclaiming procedures and equipmentSC Mechanical Code refrigerant quantity limits, machinery room requirements, and system classificationEquipment and Instruments for Refrigerant Handling and Service
Load Calculations 7 Q · 9%
Heating and cooling temperature difference (HTD and CTD) calculationsThermal resistance, conductance, and U-values for building assembliesFenestration load procedures using Heat Transfer Multipliers (HTM)Opaque panel heating and cooling loads (walls, ceilings, floors, doors)Infiltration load estimation methods (ACH table, component leakage area, blower door)Duct load factors for heating, sensible cooling, and latent coolingInternal loads (occupants, appliances, lighting)Engineered ventilation sensible and latent load calculationsHeating and Cooling Loads
Heating and Cooling Equipment 1 Q · 1%
Heating and cooling load calculations (Manual J methodology)Thermal resistance, conductance, and transmittance values (R-, C-, U-, K-values)Indoor and outdoor design temperatures for heating and coolingGas-fired furnace components, ignition systems, and combustion efficiencyHeat pump types, components, and operating modes (air-source and ground-source)Hydronic heating system components, boiler types, and controlsOil-fired heating system operation, combustion testing, and fuel deliveryElectric heating systems, element types, and equipment sizingHydronic Heating Fundamentals
Air Compressors 1 Q · 1%
Compressor drive configurations (open-drive, semi-hermetic, and fully hermetic)Reciprocating compressor components and operation (pistons, crankshaft, connecting rods, valves, valve plates)Rotary compressor types (rotating-vane and stationary-blade operation)Scroll compressor operation and applicationsScrew compressor operation and capacity controlCentrifugal compressor components and operationCompressor lubrication systems (splash vs. pressure systems)Crankcase heaters and compressor cooling systemsCompressors
Testing, Adjusting, and Balancing (TAB) 2 Q · 2%
Airflow measurement instruments and techniques (flow hoods, anemometers, pitot tubes, manometers)Balancing damper adjustment procedures for achieving design CFM at each outletDuct leakage testing methods (duct blaster/calibrated airflow matching system) and maximum allowable leakage limitsBlower door testing procedures and ACH50 calculations for building envelope airtightnessMaximum air velocity limits for trunk ducts, branch ducts, supply outlets, and return grilles (Table N3-1)System operating point determination using blower performance curves and duct system resistance curvesDuct noise identification and correction (noise sources, carriers, and amplifiers)Duct system cleaning procedures, tools, and IAQ considerationsVentilation System Service
HVACR Control Fundamentals 1 Q · 1%
Thermostat types and sensing elements (bimetal, thermistor, mercury switch, hydraulic)Low-voltage, line-voltage, and millivolt thermostat operation and wiringHeat anticipators and cooling anticipatorsProgrammable and digital thermostat features, programming, and Wi-Fi/smart controlsControl system fundamentals: set point, cut-in, cut-out, range, and differential adjustmentPressure motor controls (high-pressure, low-pressure, oil pressure safety controls)Motor starting relays (current relay, potential relay, solid-state relay, PTC relay) and contactorsElectrical test instruments and procedures (voltmeter, ohmmeter, ammeter, multimeter, megohmmeter)Thermostats
Control Schematics and Wiring Diagrams 1 Q · 1%
Pictorial diagrams vs. ladder diagramsSchematic symbols for HVACR electrical componentsControl system fundamentals: cut-in, cut-out, range, and differential adjustmentsTemperature motor controls: sensing bulbs, bimetal devices, and electronic sensorsPressure motor controls: high-pressure, low-pressure, and oil pressure controlsMotor starting relays: current, potential, solid-state, and PTC relaysMotor protection devices: fuses, circuit breakers, and bimetal/thermistor overload protectorsDirect digital control (DDC) systems: open-loop vs. closed-loop control, sensors, controllers, and actuatorsElectrical Control Systems
HVACR Control Systems 1 Q · 1%
Thermostat types and sensing elements (line-voltage, low-voltage, millivolt, bimetal, thermistor)Thermostat wiring terminals and circuit diagrams (ladder and pictorial diagrams)Heat and cooling anticipators (system lag, system overshoot, temperature swing)Programmable and digital thermostats (Wi-Fi, learning, scheduling, DIP switches)Pressure motor controls (high-pressure, low-pressure, oil pressure safety controls)Motor starting relays (current, potential, solid-state, PTC relays)Motor protection devices (fuses, circuit breakers, overload protection)Zoned systems and free cooling (dampers, economizers, zone control)Thermostats
Machine Room 1 Q · 1%
Machinery room design and construction requirements (Section 1105 general requirements)Machinery room ventilation requirements (normal and emergency airflow rates)Refrigerant detector requirements and emergency system activationMeans of egress requirements for machinery rooms over 1,000 square feetFuel-burning appliance restrictions in machinery roomsSpecial requirements for flammable refrigerant machinery rooms (Groups A2, A3, B2, B3)Special requirements for Group A2L refrigerant machinery roomsRemote controls and emergency shutoff switches for machinery room equipmentRefrigeration
Air Conditioning Systems 3 Q · 4%
Compression refrigeration cycle components and operationResidential central air-conditioning system types (unitary vs. field-erected, split systems)Ductless and self-contained air-conditioning systems (room units, PTAC, mini-splits)Commercial air-conditioning systems (rooftop units, chillers, cooling towers)Heat pump operation, types, and components (air-source, ground-source, reversing valve)Metering devices (capillary tubes, TXV, EEV, fixed-orifice)Heating and cooling load calculations (Manual J, heat transfer values, design temperatures)Thermostat types, wiring, and controls for cooling systemsThermostats
Heat Pumps 4 Q · 5%
Heat pump operating modes (heating and cooling cycle refrigerant flow)Types of heat pumps (air-source vs. ground-source)Reversing valve operation and connectionsHeat pump system components (accumulator, compressor, metering devices, coils)Defrost methods and controls (reverse cycle and electric heat defrost)Auxiliary heat and balance pointHeat pump efficiency ratings (EER, SEER, HSPF, COP)Heat pump installation, maintenance, and troubleshootingHeat PumpsResidential Central Air-Conditioning Systems
Furnaces (Warm Air Heating Equipment) 2 Q · 2%
Gas furnace combustion principles and fuel types (natural gas vs. LP gas)Gas ignition systems (standing-pilot, intermittent-pilot, DSI, and HSI)Gas furnace safety controls (high-limit switch, rollout switch, pressure switch)Gas furnace efficiency ratings and categories (AFUE, Category I–IV venting)Oil furnace components and operation (gun burner, fuel unit, primary control unit, cad cell relay)Electric furnace heating elements and sequencer controlsCombustion venting systems and vent connector requirements (SC Fuel Gas Code)Heat pump auxiliary heat, defrost controls, and reversing valve operationOil-Fired Heating Systems
Specialized Heaters 2 Q · 2%
Electric heating element types (open wire, open ribbon, tubular cased wire)Electric furnace and duct heater controls (sequencers, contactors, airflow switches)Electric baseboard heating unit installation and controlsElectric radiant heating systems (direct and indirect infrared, radiant floor and ceiling panels)Safety controls for electric heating systems (high-limit switches, fusible links, overcurrent protection)Gas-fired specialized heaters (vented/unvented room heaters, wall furnaces, floor furnaces, unit heaters, infrared radiant heaters)Sauna heater installation requirements (guards, temperature/timer controls, ventilation, warning notices)Pool and spa heater installation requirementsElectric Heating Systems
Chimneys, Flues, Vents, and Vent Connectors 3 Q · 4%
Appliance venting categories (Category I, II, III, IV) and vent type selectionVent and chimney termination height and location requirementsSizing of venting systems using code tables for Category I appliancesVent connector materials, clearances, slope, and installation requirementsMasonry chimney construction, flue lining systems, and cleanout requirementsDraft hoods, draft controls, and barometric draft regulatorsDirect-vent, mechanical draft, and power exhauster systemsCondensate drainage requirements for Category II and IV appliancesOil-Fired Heating SystemsChimneys and VentsGas-Fired Heating Systems
Combustion Air 2 Q · 2%
Indoor combustion air requirements (volume and standard method calculations)Outdoor combustion air provisions (two-opening and one-opening methods)Combustion air opening sizing, location, and minimum dimensionsCombustion air ducts (materials, termination, and installation requirements)Louvers, grilles, and screens for combustion air openingsMechanical combustion air supply and appliance interlock requirementsCombustion air requirements for oil-fired appliances (NFPA 31)Dampered combustion air openings and interlock with firing cycleGas Piping Installations
General Fuel Knowledge 1 Q · 1%
Combustion process and chemistry (stoichiometric, complete, and incomplete combustion)Properties and characteristics of natural gas and LP/propane gasGas piping materials, sizing, and pressure requirementsFuel oil grades, properties, and storage systemsCombustion air requirements for gas-fired and oil-fired appliancesVenting and chimney systems for fuel-burning appliancesIgnition systems and gas valve controls for gas-fired equipmentCombustion efficiency testing (CO2, stack temperature, draft, and smoke tests)Gas Piping Installations
Natural Gas 2 Q · 2%
Gas piping materials and fittings (steel, copper, CSST, polyethylene)Gas piping sizing methods and pressure drop calculationsAllowable operating pressures and pressure testing requirementsCombustion air requirements for gas-fired appliancesVenting system types and appliance categories (Category I–IV)Vent and chimney sizing, termination, and clearance requirementsGas furnace components, ignition systems, and safety controlsCombustion efficiency, flue gas analysis, and AFUE ratingsGas Piping Installations
LP Gas 2 Q · 2%
LP gas piping system design and sizing (pressure drop, pipe sizing tables, and methods)Approved piping materials and fittings for LP gas systems (steel, copper, CSST, polyethylene)LP gas storage tank installation requirements and NFPA 58 complianceTwo-stage regulator systems for LP gas (first-stage and second-stage pressure regulation)LP gas system pressure testing, leak checks, and purging proceduresCombustion characteristics of LP gas (specific gravity, BTU content, flammability limits, air-fuel ratios)Venting requirements for LP gas appliances (categories, vent types, termination clearances)LP gas appliance installation requirements (clearances, ignition source elevation, prohibited locations)Gas Piping Installations
General Duct Systems Knowledge and Principles 4 Q · 5%
Pressure units and blower performance curves (IWC, ESP, CFM relationships)Available static pressure calculation and component pressure lossesTotal effective length and friction rate determinationFitting equivalent lengths and duct run resistanceAir velocity limits for supply and return ductsDuct system types and configurations (radial, extended plenum, reducing trunk, perimeter loop)Duct materials, construction standards, and insulation requirementsDuct leakage, sealing methods, and system efficiencyAir DistributionDuct Systems
Duct Conversions/Equivalencies 4 Q · 5%
Round-to-rectangular duct conversion using equal friction rate equivalency tablesRound-to-oval duct conversion using equal friction rate equivalency tablesFriction chart use to determine round duct diameter from CFM and friction rateFriction rate calculation from available static pressure and total effective lengthDuct sizing slide rule equations for round duct diameter by material typeFitting equivalent length concept and conversion to pressure dropRoughness factors and friction chart corrections for different duct materialsEquivalent length adjustment for non-default velocity and friction rate conditionsDuct Sizing CalculationsBasic Duct Sizing Principles
Mechanical Sheet Metal Devices/Systems 2 Q · 2%
Duct system types and configurations (radial, extended plenum, reducing trunk, perimeter loop)Duct sizing procedure using ACCA Manual D (friction rate, available static pressure, total effective length)Sheet metal duct construction materials, gauges, and fabrication standardsDuct joints, seams, and sealing methods (mastic, UL 181 tapes, mechanical fasteners)Fitting equivalent lengths and their effect on critical circulation pathFire and smoke dampers: ratings, actuation, and installation requirementsDuct insulation requirements, vapor retarders, and R-value standardsDuct leakage testing, sealing requirements, and system efficiency impactsAir Distribution
Duct System Components 5 Q · 6%
Duct system configurations (radial, extended plenum, reducing trunk, perimeter loop)Supply and return air fitting equivalent lengths and pressure lossesAvailable static pressure calculation and component pressure drop deductionsDuct materials (sheet metal, fibrous glass duct board, flexible wire helix)Registers, diffusers, grilles, and supply outlet selectionDamper types and functions (balancing, fire, smoke, zone)Duct insulation requirements and vapor retardersDuct sealing requirements and leakage testing (duct blaster, mastic, tape)Air Distribution
Metal Ducts 3 Q · 4%
Metal duct sheet metal thickness requirements by duct size and static pressure classificationDuct classification by operating pressure and SMACNA construction standardsJoints, seams, and connections in metallic ducts — fastening and sealing methodsRound-to-rectangular equivalent duct sizing and aspect ratio considerationsAir velocity limits in metal supply and return trunk and branch ductsFitting equivalent lengths for elbows, takeoffs, boots, and transitionsDuct leakage effects on system performance and required sealing practicesFire and smoke damper requirements for metallic ducts penetrating rated assembliesAir Distribution
Fiberglass Ducts 1 Q · 1%
Fibrous glass duct construction standards and code compliance (NAIMA, SMACNA, UL 181)EI pressure rating classifications for fiberglass duct board (475, 800, 1400)Seams, joints, and closure systems for fibrous glass ductwork (UL 181A-P, 181A-M, 181A-H tapes and mastics)Reinforcement, hangers, and supports for fiberglass duct systemsRecommended installation locations for rigid fiberglass duct boardDuct board friction rate and airway sizing using duct slide rule (vs. sheet metal equivalents)Leakage class characteristics of fibrous glass duct systems and sealing requirementsTemperature limitations for nonmetallic fiberglass ductwork (250°F maximum per SC Mechanical Code)Duct Systems
Filtering Systems 1 Q · 1%
Types of air filters (disposable, washable, electrostatic, carbon, HEPA)MERV ratings and filter efficiency standardsAir filter testing and measurement methods (atmospheric dust spot efficiency, synthetic dust weight arrestance, fractional efficiency, DOP HEPA method)Electronic air cleaner operation and maintenanceUltraviolet (UVG) germicidal light systems installation and maintenanceIonizing air purifiers and ozone considerationsFilter pressure drop measurement and replacement intervalsHeat recovery ventilators (HRV) and energy recovery ventilators (ERV)Air Distribution
Ventilation Equipment and Devices 1 Q · 1%
Minimum outdoor airflow rates and ventilation rate calculations by occupancy typeMechanical vs. natural ventilation requirements and intake opening location/protection rulesExhaust system requirements by occupancy and contaminant type (cooking, dryers, hazardous materials, garages)Duct construction, materials, sizing, sealing, and insulation requirementsRegisters, diffusers, grilles, dampers, and airflow balancingFire and smoke dampers: installation, ratings, and actuation requirementsAirflow measurement instruments and testing methods (blower door, duct blaster, flow hoods, anemometers)Ventilation load calculations for heating and cooling (sensible and latent) including heat recovery equipmentExhaust Systems
Exhaust Systems 2 Q · 2%
Exhaust discharge location requirements and minimum separation distancesCommercial kitchen Type I and Type II hood systemsClothes dryer exhaust duct installation and length limitationsHazardous exhaust systems for flammable vapors, dusts, and toxic materialsSmoke control system design and equipment requirementsMakeup air requirements for exhaust systemsVentilation system balancing, airflow measurement, and duct testingEnergy recovery ventilation systems and prohibited applicationsExhaust SystemsAir Distribution
Safety 2 Q · 2%
Lockout/tagout (LOTO) procedures for electrical, hydraulic, pneumatic, and mechanical systemsPersonal protective equipment (PPE) selection and requirements — head, eye, hearing, respiratory, and foot protectionFire hazards and fire extinguisher classes, types, and PASS techniqueFall protection systems — guardrail systems, personal fall arrest systems, and safety netsConfined space entry requirements — permit spaces, atmospheric testing, and attendant dutiesElectrical safety — grounding, GFCI protection, working clearances, and overcurrent protectionHazard communication — safety data sheets (SDS), GHS pictograms, and chemical/refrigerant hazardsSafe work practices — ladder and scaffold safety, proper lifting, and first aid proceduresSubpart D-Occupational Health and Environmental Controls

Key Distinctions

Single screw compressorvsTwin screw compressor

A single screw compressor uses one main rotor that meshes with two star-shaped rotors driven by the main rotor, while the basic operating principles are the same as other screw compressors.

Modern Refrigeration and Air Conditioning (20th ed.), Chapter 18, Section 18.2.4 — Single Screw Compressor
Type B-W gas vent terminationvsType B or L gas vent termination

A Type B-W gas vent shall terminate not less than 12 feet in vertical height above the bottom of the wall furnace, whereas Type B or L gas vents must terminate not less than 5 feet above the highest connected appliance draft hood or flue collar.

SC Fuel Gas Code 2021, Chapter 5 Chimneys and Vents, Section 503.6.6
Appliance shutoff valve in the same room (409.5.1)vsAppliance shutoff valve at a manifold (409.5.3)

The same-room option uses the 6-foot limit, while a readily accessible, permanently identified manifold valve shall be located within 50 feet of the appliance served (with piping from the manifold to within 6 feet of the appliance designed, sized and installed per Sections 401 through 408).

SC Fuel Gas Code 2021, Chapter 4 — Section 409.5.3 Located at Manifold
Double flarevsSingle flare

Double flares are made with a double thickness of tubing metal and are stronger, but are recommended only for tubing 5/16" OD and larger because they are not easily formed on smaller tubing (1/4" lines are single-flared).

Modern Refrigeration and Air Conditioning (20th ed.), Page 148
Plastic pipe operating pressure — natural gasvsPlastic pipe operating pressure — LP-gas

Plastic pipe installed outdoors underground only shall not be operated at pressures greater than 100 psig for natural gas or greater than 30 psig for LP-gas.

SC Fuel Gas Code 2021, Chapter 4 — Section 404.17.1 Limitations
Thimble 4 inches larger (listed draft-hood appliance, short open run)vsThimble 2 inches larger (listed draft-hood appliance, open run not less than 6 feet)

For listed appliances with draft hoods and appliances listed for Type B gas vents the ventilated thimble shall be not less than 4 inches larger in diameter than the single-wall metal pipe, but it is permitted to be not less than 2 inches larger where there is a run of not less than 6 feet of pipe in the open between the draft hood outlet and the thimble; 6 inches applies to unlisted appliances with draft hoods and 12 inches to residential and low-heat appliances.

SC Fuel Gas Code 2021, Chapter 5 — Section 503.7.7 (Single-Wall Penetrations of Combustible Walls)
Heat loss HTMvsHeat gain HTM

A heat loss HTM is the component U-value times the temperature difference (IDT – ODT), while a heat gain HTM adjusts that same difference for factors such as sun exposure and heat storage and is generally looked up on a chart rather than calculated.

Modern Refrigeration and Air Conditioning (20th ed.), Page 992
Thermostat terminal OvsThermostat terminal B

O energizes the reversing valve for cooling mode and B energizes it for heating mode (shown as a combined O/B terminal); L is system monitor/service light and W2 is heating stage 2 or auxiliary heat, and thermostats should be wired by terminal letter, not wire color.

Modern Refrigeration and Air Conditioning (20th ed.), Page 1102 — Section 40.5.1 Temperature Controls
Category I / Category II gas appliance ventingvsCategory III / Category IV gas appliance venting

Category I is negative-pressure noncondensing (Class B vent) and Category II is negative-pressure condensing (special vent material specified by the manufacturer), while Category III is positive-pressure noncondensing (stainless steel) and Category IV is positive-pressure condensing (PVC).

Modern Refrigeration and Air Conditioning (20th ed.), Page 1134
Pressure lubrication systemvsSplash lubrication system

Pressure lubrication delivers oil under pressure to all bearing surfaces, so the compressor runs quieter even with greater bearing clearances because the pressurized oil cushions the bearings.

Modern Refrigeration and Air Conditioning (20th ed.), Chapter 18, Section 18.3.4 — Pressure Lubrication
Thermostatic blower control cut-invsThermostatic blower control cut-out

A thermostatic blower control closes its contacts to start the blower at a plenum temperature of about 140°F (60°C) and opens its contacts when the plenum cools to about 90°F (32°C) after burner shutdown.

Modern Refrigeration and Air Conditioning (20th ed.), Page 1029
Wider thermostat differential (e.g., 26°F cut-in / 14°F cut-out)vsNarrower thermostat differential (e.g., 24°F cut-in / 16°F cut-out)

Moving cut-in and cut-out equally in opposite directions keeps the average box temperature the same; widening the differential lengthens run time and lengthens the interval between cycles, while narrowing it produces shorter, more frequent cycles.

Modern Refrigeration and Air Conditioning (20th ed.), Pages 355–357 (Section 16.2.2 Differential Adjustment)
Power burnervsAtmospheric gas burners (ribbon, slotted, inshot)

A power burner uses a blower to force both primary and secondary air into the burner tube and is required for fuel oil, while atmospheric gas burners rely on the siphoning/venturi action of gas flowing through an orifice and are used with fuel gas.

Modern Refrigeration and Air Conditioning (20th ed.), Page 1124
Manual J default sealed duct leakage — supply sidevsManual J default sealed duct leakage — return side

The default base-case leakage rate for sealed duct systems is 0.12 Cfm/SqFt of duct surface area on the supply side and 0.24 Cfm/SqFt on the return side (0.35 is the unsealed supply default).

Manual J, Section 1-8 and Section 23-1

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 is required).
Class 2 circuit Modern Refrigeration and Air Conditioning (20th ed.), Page 296 (Section 13.2.2 Electrical Codes)
A remote-control circuit such as thermostat wiring supplied by a power source whose output is no greater than 30 V and 1000 VA, which HVACR personnel are permitted to install (but not the branch, power-supply or service conductors feeding the equipment).
Clearance space (reciprocating compressor) Modern Refrigeration and Air Conditioning (20th ed.), Chapter 18, Section 18.2.1 — Clearance Space
The small volume remaining between the piston at top dead center and the valve plate, approximately .010″ to .020″ (.254 mm to .508 mm).
Swaged connection Modern Refrigeration and Air Conditioning (20th ed.), Pages 160–161
A joint made by expanding one tube end so a like-size tube is inserted and brazed, with the overlap length equal to the outside diameter of the tubing (3/4" ACR tubing requires a 3/4" overlap).
Brazing joint clearance Modern Refrigeration and Air Conditioning (20th ed.), Page 158
The 0.001" to 0.005" gap between tube and fitting socket that offers maximum joint strength and soundness; a press fit is too tight for capillary penetration and excessive clearance can crack under stress or vibration.
Wet-rotor circulating pump Modern Refrigeration and Air Conditioning (20th ed.), Page 1039
A centrifugal hydronic pump whose bearings are lubricated by the circulating system water, eliminating the need for a shaft seal and reducing noise and maintenance.
System-dependent (passive) recovery equipment Modern Refrigeration and Air Conditioning (20th ed.), Appendix G — Type II (high- or very high-pressure appliances), Recovery Requirements, Page 1570
Recovery equipment that relies on the system itself; its use is prohibited on any system containing more than 15 pounds of refrigerant (5 lb defines a small appliance, 50 lb is the leak-repair charge threshold, 200 lb changes required evacuation vacuum levels).
Heat transfer multiplier (HTM) Modern Refrigeration and Air Conditioning (20th ed.), Page 992
A building component's U-value multiplied by a temperature difference, entered per component on a load-calculation worksheet.
Type I hood exhaust fan sensor activation SC Mechanical Code 2021, Chapter 5, Section 507.1.1 (Operation)
Where one or more temperature or radiant energy sensors activate the Type I hood exhaust fan, the fan must activate not more than 15 minutes after the first appliance served by that hood is turned on.
Combustion air through stud/joist spaces (SC Mechanical Code 304.11, Item 1 Exception) South Carolina Mechanical Code, Chapter 3 (General Regulations), Section 304.11, Item 1 Exception
Unobstructed stud and joist spaces within dwelling units are permitted to convey combustion air provided that not more than one required fireblock is removed.
Fire damper hourly rating Modern Refrigeration and Air Conditioning (20th ed.), Page 767
Fire damper hour ratings must be 75% of the hour rating of the wall, floor or partition penetrated, so a 2-hour barrier uses a 1.5-hour damper.
Category II gas appliance Modern Refrigeration and Air Conditioning (20th ed.), Page 1134
An appliance whose vent operates under negative pressure with flue gas leaving below its dew point so condensate forms, requiring special vent material specified by the manufacturer.
Charge compensator tank Modern Refrigeration and Air Conditioning (20th ed.), Page 1089
A heat pump canister that stores excess liquid refrigerant; the gas line passes through it without opening into it, while the smaller liquid line connects to and fills the tank during heating mode.
Oil injection (screw compressor) Modern Refrigeration and Air Conditioning (20th ed.), Chapter 18, Section 18.2.4 — Oil Injection
Injected oil seals the clearance between the rotors and the cylinder to prevent refrigerant leakage and helps cool the compressor, contributing to high efficiency.
Fully hermetic compressor construction Modern Refrigeration and Air Conditioning (20th ed.), Chapter 18, Section 18.1.2 — Fully Hermetic Compressors, Construction
The compressor and motor are usually spring-mounted inside the hermetic dome (some use external mounting springs) with flexible internal discharge and suction lines, so most vibration is not felt outside the dome.
ASHRAE 99 percent design value ACCA Manual J (8th ed.), Section 18-1, Page 18-2 (PDF Page 164)
The outdoor dry-bulb temperature basis for residential heating loads, meaning the outdoor temperature will be colder than the design value about 1 percent of total cold-month hours (about 85 to 90 hours per year).
Defrost cut-out temperature (thermistor-terminated defrost) Modern Refrigeration and Air Conditioning (20th ed.), Page 524 — Section 21.1.9 Evaporator Defrost Controls
The evaporator coil temperature, around 40°F, at which the thermistor signals the defrost control to end defrost and resume normal refrigeration.
Impulsive or impact noise limit (29 CFR 1926.52(e)) OSHA 29 CFR 1926, §1926.52(e)
Employee exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level, a separate limit from the duration-based continuous levels in Table D-2 (e.g., 90 dBA for 8 hours).

Formulas to Know

Heating heat transfer multiplier for a componentHTM (Btuh/SqFt) = assembly U-value × HTD; e.g., 0.07 × 50 = 3.50, 0.07 × 75 = 5.25, 0.10 × 60 = 6.00
Component heating load (Q = U × area × temperature difference)Load (Btuh) = HTM × load area; e.g., wall 136 sq ft × 3.50 = 476 Btuh; glass 60 sq ft × (0.30 × 50 = 15.00) = 900 Btuh; ceiling 140 sq ft × (0.03 × 50 = 1.50) = 210 Btuh; door 20 sq ft × (0.50 × 70 = 35.00) = 700 Btuh (fenestration load area is the rough-opening area)
Net exposed wall areaNet wall = (exposed wall length × wall height) − window area − door area; e.g., 24 ft × 9 ft = 216 sq ft − (2 × 30 glass + 20 door) = 136 sq ft
Infiltration airflow from air changesCFM = (air changes per hour × room volume) ÷ 60; e.g., 0.6 × (16 × 14 × 10 = 2,240 cu ft) ÷ 60 = 22.4 cfm
Infiltration heating loadBtuh = 1.1 × ACF × CFM × HTD; e.g., 1.1 × 1.00 × 22.4 × 70 = 1,725 Btuh; 1.1 × 1.00 × 15.4 × 60 = 1,014 Btuh
Rescaling total heating load for a colder outdoor design temperatureNew total = old total × (new HTD ÷ old HTD) because every component is proportional to HTD; e.g., 4,820 × (80 ÷ 70) = 5,509 Btuh; 2,958 × (70 ÷ 60) = 3,451 Btuh
Room total heating loadTotal = wall + glass + door + ceiling + infiltration; e.g., 770 + 1,155 + 700 + 470 + 1,725 = 4,820 Btuh; and 1,008 + 504 + 432 + 1,014 = 2,958 Btuh
Total equivalent length of a duct runTEL = sum of straight measured lengths + elbow equivalent allowances; e.g., (28 + 22 + 15 = 65 ft) + (2 elbows × 25 ft = 50 ft) = 115 ft
Duct friction loss for a runFriction loss = (total equivalent length ÷ 100) × friction rate; e.g., (115 ÷ 100) × 0.10 in. WC = 0.115 in. WC
Mixed-air temperature and outdoor-air percentageT_mix = (Return CFM × Return Temp + Outdoor CFM × Outdoor Temp) ÷ Total CFM, and OA% = Outdoor CFM ÷ Total CFM; e.g., (3,000 × 60 + 1,000 × 92) ÷ 4,000 = 68.0 °F and 1,000 ÷ 4,000 = 25%
Additional refrigerant charge for a long line set (per the figure's line-set data)Added feet = total line-set length − the length covered by the factory charge; added charge = added feet × the given oz-per-foot rate (÷ 16 oz/lb for pounds); e.g., with the figure's 15 ft factory coverage and 0.6 oz/ft: 65 − 15 = 50 ft × 0.6 = 30.0 oz ≈ 1.9 lb
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