Exam Cheat Sheet · Quick Reference
ICC F32 Residential Mechanical (Class C) Exam (2015 IRC)
National · Pearson Vue
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
70
Passing score
70%
Exam time
180 min
Administered by
Pearson Vue
Format
Reference materials allowed
National State Portion 70 questions
General Requirements
22 Q · 32%
Appliance access and working space clearances (attic, underfloor, alcove, and room installations)Clearances from combustible construction and clearance reduction methodsAppliance labeling requirements and nameplate informationAppliance installation requirements (anchorage, ignition source elevation, seismic strapping, garage protection)Mechanical administration: scope, existing system alterations, and maintenance responsibilitiesExhaust systems: clothes dryer exhaust ducts, range hoods, and mechanical ventilation ratesHydronic piping materials, support intervals, testing requirements, and floor heating systemsOil tank and oil piping installation, special piping storage systems, and solar thermal energy system requirementsGeneral Mechanical System RequirementsHydronic PipingExhaustSolar Thermal Energy Systems
+2 more
Appliances and Equipment
4 Q · 6%
Equipment sizing requirements (ACCA Manual J and Manual S)Clearances, access, and serviceability requirements for heating and cooling equipmentCondensate disposal, auxiliary drain pans, and water-level monitoring devicesRefrigerant piping insulation, protection, and locking access port capsBoiler safety controls, pressure-relief valves, gauges, and low-water cutoffsExpansion tanks for hot water boiler systemsWater heater installation requirements, prohibited locations, and standardsSpecial appliances installation requirements (ranges, sauna heaters, fuel cell power plants)
Duct Systems
11 Q · 15%
Duct construction standards and material requirements (above-ground and underground)Duct sealing — joints, seams, and connection fastening methodsDuct insulation materials — flame spread/smoke-developed ratings and R-value labelingDuct support requirements by duct typeUse of stud wall cavities and joist spaces as air plenumsReturn air opening restrictions and prohibited source locationsUnder-floor plenum requirements and prohibitionsIndependent garage HVAC systems — supply and return air restrictions
Combustion Air
16 Q · 23%
Indoor combustion air volume requirements (standard method and known air-infiltration-rate method)Outdoor combustion air opening methods (two-permanent-openings and one-permanent-opening)Combination indoor and outdoor combustion air provisionsMechanical combustion air supply systems and appliance interlock requirementsCombustion air duct construction and installation requirementsLouvers, grilles, and screens for combustion air openings (net free area calculations)Combustion air requirements for solid-fuel, oil-fired, and gas-fired appliances by fuel typeFuel Gas
Chimneys and Vents
7 Q · 10%
Venting system types and applications (Type B, Type BW, Type L, single-wall metal pipe, special gas vent)Chimney and vent termination height requirementsVent connector installation requirements (slope, clearances, length, materials)Sizing of Category I appliance venting systems using IRC tablesMasonry chimney requirements (flue lining, cleanouts, connections, inspection)Factory-built chimney listing and installation requirementsDraft hoods, draft regulators, and automatically operated vent dampersFuel Gas
Fuel Supply Systems
10 Q · 14%
Gas piping materials and tubing types (steel, copper, CSST, polyethylene plastic)Gas pipe sizing methods and sizing tables (longest length, branch length, hybrid pressure)Piping system installation requirements (prohibited locations, underground burial depth, protection from physical damage)Pressure testing, leak detection, and purging proceduresShutoff valves and flow controls (appliance shutoff valves, pressure regulators, excess flow valves)Electrical bonding requirements for gas piping (CSST bonding, bonding jumper specifications)Appliance connections and connectors (maximum length, prohibited penetrations, union requirements)Fuel oil storage tanks and piping systems (tank types, installation, fill/vent piping, shutoff valves)Fuel Gas
Key Distinctions
Two outdoor combustion air openings through horizontal ductsvsTwo outdoor combustion air openings communicating directly or through vertical ducts
Horizontal ducts require each opening to have not less than 1 square inch of free area per 2,000 Btu/h of total input, while direct openings or vertical ducts require only 1 square inch per 4,000 Btu/h per opening (2015 IRC G2407.6.1).
IRC 2015 Section G2407.6.1 (304.6.1)Two-permanent-openings outdoor air methodvsOne-permanent-opening outdoor air method
The one-opening method requires 1 square inch per 3,000 Btu/h of total input and not less than the sum of the areas of all vent connectors in the enclosure, versus the two-opening rates of 1 per 2,000 (horizontal duct) or 1 per 4,000 Btu/h (direct/vertical) each.
IRC 2015 Section G2407.6.2 (304.6.2)Wood louvers (design/free area unknown)vsMetal louvers and grilles (design/free area unknown)
Where the design and free area are not known, wood louvers are assumed to have 25-percent free area and metal louvers and grilles are assumed to have 75-percent free area (G2407.10 / M1307.4.1.2).
IRC 2015 Section G2407.10 (304.10)Louver free area knownvsLouver free area not known
Where the free area through a louver, grille or screen design is known, that known free area is used to size the opening; only where it is unknown are the 25-percent (wood) and 75-percent (metal) assumptions applied.
IRC 2015 Section G2407.10 (304.10)Indoor combustion air — standard methodvsIndoor combustion air — known air infiltration rate method
The standard method requires 50 cubic feet per 1,000 Btu/h of total input, while the known-air-infiltration-rate method uses Equation 24-1 or 24-2 and must be used where the known infiltration rate is less than 0.40 ACH.
IRC 2015 Section G2407.5.1 (304.5.1)Equation 24-1 (appliances other than fan-assisted)vsEquation 24-2 (fan-assisted appliances)
Equation 24-1 uses the 21/ACH factor for other-than-fan-assisted appliances and Equation 24-2 uses the 15/ACH factor for fan-assisted appliances (G2407.5.2).
IRC 2015 Section G2407.5.2 (304.5.2)Indoor openings combining spaces on the same storyvsIndoor openings connecting spaces in different stories
Same-story openings require each opening to have 1 square inch per 1,000 Btu/h of total input but not less than 100 square inches, while spaces in different stories are considered communicating where openings in doors or floors provide a total minimum free area of 2 square inches per 1,000 Btu/h.
IRC 2015 Section G2407.5.3.1 (304.5.3.1)Appliances sized by the prescriptive combustion air methodsvsAppliances provided combustion air per the manufacturer's instructions
Category I natural-draft and draft-hood-equipped gas appliances use the prescriptive methods of G2407.5 through G2407.9, while direct-vent appliances, gas appliances of other than natural draft design, vented gas appliances not designated as Category I, appliances with power burners, and solid fuel-burning appliances (M1701.1) follow the manufacturer's instructions.
IRC 2015 Section G2407.1 (304.1)Radiant piping in slab-on-grade applicationsvsRadiant piping in suspended floor joist bay applications
Slab-on-grade requires insulating material with a minimum R-value of 5 beneath the piping (M2103.2.1), while suspended floor applications require minimum R-11 insulation in the joist bay cavity serving the heated space above (M2103.2.2).
IRC 2015 Section M2103.2.1Clothes dryer exhaust duct (specified-length method)vsTransition duct
The exhaust duct maximum length is 35 feet from the connection to the transition duct to the outlet terminal (reduced for fittings per Table M1502.4.5.1), while the transition duct is a single listed length not greater than 8 feet, not concealed in construction, and not counted in the 35 feet.
IRC 2015 Section M1502.4.5.1Attic passageway limited to 20 feetvsAttic passageway permitted up to 50 feet
The passageway from the attic opening to the appliance is limited to not more than 20 feet measured along the centerline; 50 feet is permitted only where the passageway is unobstructed and not less than 6 feet high and 22 inches wide for its entire length (M1305.1.3).
IRC 2015 Section M1305.1.3Draft hoodvsBarometric draft regulator
A draft hood is a nonadjustable device built into an appliance or vent connector that permits escape of flue gases with no draft, prevents backdraft entry and neutralizes stack action, while a barometric draft regulator is a balanced damper device attached to a chimney, vent connector, breeching or flue gas manifold that controls chimney draft (double-acting types move either way to protect against excessive draft and backdraft).
IRC 2015 Section G2403 (202) — definition of DRAFT HOODShield plates for concealed mechanical pipingvsClothes dryer exhaust duct metal/shield thickness
Concealed mechanical piping shield plates must be steel not less than 0.0575 inch (No. 16 gage) per M1308.2.3, whereas 0.062 inch applies to dryer exhaust duct shield plates (M1502.5) and 0.0157 inch (No. 28 gage) is the minimum dryer duct metal thickness.
IRC 2015 Section M1308.2.3Key Terms
Draft hood IRC 2015 Section G2403 (202) — definition of DRAFT HOOD
A nonadjustable device built into an appliance, or made part of the vent connector, that permits ready escape of flue gases in the event of no draft, prevents backdraft from entering the appliance, and neutralizes the effect of stack action of the chimney or gas vent on appliance operation (IRC 2015 G2403 (202)).
Barometric draft regulator IRC 2015 Section G2403 (202) — definition of BAROMETRIC DRAFT REGULATOR
A balanced damper device attached to a chimney, vent connector, breeching or flue gas manifold that protects combustion appliances by controlling chimney draft; a double-acting regulator's balancing damper is free to move in either direction to protect against both excessive draft and backdraft (G2403 (202)).
Flue collar IRC 2015 Section G2403 (202) — definition of FLUE COLLAR
That portion of an appliance designed for the attachment of a draft hood, vent connector or venting system (G2403 (202)).
Mechanical or induced draft IRC 2015 Section G2403 (202) — definition of DRAFT (Mechanical or induced draft)
The pressure difference created by the action of a fan, blower or ejector located between the appliance and the chimney or vent termination (G2403 (202)).
Venting system IRC 2015 Section G2403 (202) — definition of VENTING SYSTEM
A continuous open passageway from the flue collar or draft hood of an appliance to the outdoor atmosphere for removing flue or vent gases, usually composed of a vent or chimney and a vent connector, if used (G2403 (202)).
Ratio of interior spaces (combination indoor/outdoor combustion air) IRC 2015 Section G2407.7.3 (304.7.3)
The available volume of all communicating spaces divided by the required volume; the outdoor opening size reduction factor is one minus that ratio (G2407.7.3 (304.7.3)).
Transition duct (clothes dryer) IRC 2015 Section M1502.4.3
A single length listed and labeled to UL 2158A connecting the dryer to the exhaust duct, not greater than 8 feet in length and not concealed within construction (M1502.4.3).
Appliance working space IRC 2015 Section M1305.1
A level working space not less than 30 inches deep and 30 inches wide in front of the control side to service an appliance (M1305.1).
Furnace/air handler compartment or alcove IRC 2015 Section M1305.1.1
An enclosing space requiring a minimum 3-inch working space along the sides, back and top, with the total width not less than 12 inches wider than the furnace or air handler (and 6 inches at the front combustion chamber side where the firebox is open to the atmosphere) (M1305.1.1).
Passageway to an appliance in a compartment, alcove or basement IRC 2015 Section M1305.1.2
An unobstructed passageway not less than 24 inches wide, large enough to remove the largest appliance, reached through an opening or door, with a level service space not less than 30 inches deep at the front or service side (M1305.1.2).
Makeup air (kitchen exhaust hood) IRC 2015 Section M1503.4
Air required for exhaust hood systems capable of exhausting in excess of 400 cfm, provided at a rate approximately equal to the exhaust rate with at least one gravity or automatic electrically operated damper (M1503.4).
Intermittent whole-house mechanical ventilation IRC 2015 Section M1507.3.3
Permitted where controls enable operation for not less than 25 percent of each 4-hour segment and the required ventilation rate is multiplied by the factor from Table M1507.3.3(2) (exception to M1507.3.3).
Prohibited tee application (hydronic) IRC 2015 Section M2101.7
Fluid in the supply side of a hydronic system shall not be permitted to enter a tee fitting through the branch opening (M2101.7).
Thermal break at a heated slab IRC 2015 Section M2103.2.3
Asphalt expansion joint material or similar insulating material required where a heated slab meets a foundation wall or other conductive slab (M2103.2.3).
Pressurized thermal storage unit label IRC 2015 Section M2301.3.2
Units must be listed and labeled showing manufacturer's name, model number, serial number, maximum and minimum allowable operating temperatures and pressures, and compatible heat transfer fluids — weight is required only for collectors and panels (M2301.3.2 / M2301.3.1).
Maintenance of required safety devices IRC 2015 Section M1202.3
Devices or safeguards required by code must be maintained in compliance with the code edition under which they were installed, and mechanical systems maintained in proper operating condition per the original design (M1202.3).
Formulas to Know
Indoor combustion air volume — standard method
Required volume = 50 cubic feet per 1,000 Btu/h of total appliance input (example: 150,000 Btu/h ÷ 1,000 = 150; 150 × 50 = 7,500 cu ft) — G2407.5.1Indoor combustion air volume — known air infiltration rate method
Other than fan-assisted (Eq. 24-1): Required Volume ≥ (21/ACH) × (I ÷ 1,000 Btu/h); fan-assisted (Eq. 24-2): Required Volume ≥ (15/ACH) × (I_fan ÷ 1,000 Btu/h); total for the space is the sum of the volumes for all appliances; this method must be used where the known infiltration rate is less than 0.40 ACH (example: 0.30 ACH with a 60,000 Btu/h fan-assisted + 30,000 Btu/h natural-draft = 3,000 + 2,100 = 5,100 cu ft)Outdoor combustion air — two permanent openings
Each opening: 1 sq in free area per 2,000 Btu/h of total input where communicating through horizontal ducts; 1 sq in per 4,000 Btu/h where communicating directly with the outdoors or through vertical ducts (examples: 120,000 ÷ 2,000 = 60 sq in each; 100,000 ÷ 4,000 = 25 sq in each) — G2407.6.1Outdoor combustion air — one permanent opening
Opening free area = 1 sq in per 3,000 Btu/h of total input of all appliances in the enclosure, and not less than the sum of the areas of all vent connectors (example: 120,000 ÷ 3,000 = 40 sq in, which exceeds 28 sq in of vent connector area) — G2407.6.2Indoor combustion air — openings between communicating spaces
Same story: each opening = 1 sq in per 1,000 Btu/h of total input, not less than 100 sq in (example: 150,000 ÷ 1,000 = 150 sq in each). Different stories: openings in doors or floors with total minimum free area of 2 sq in per 1,000 Btu/h (example: 2 × 75 = 150 sq in) — G2407.5.3.1 / G2407.5.3.2Combination indoor and outdoor combustion air — reduced outdoor opening
Ratio of interior spaces = available volume ÷ required volume; reduction factor = 1 − ratio; required outdoor opening = full opening size from G2407.6 × reduction factor (example: 2,400 ÷ 6,000 = 0.4; 1 − 0.4 = 0.6; horizontal-duct opening 120,000 ÷ 2,000 = 60 sq in; 60 × 0.6 = 36 sq in each); minimum opening dimension still not less than 3 inches — G2407.7.3Mechanical combustion air supply rate
Outdoor air not less than 0.35 cfm per 1,000 Btu/h of the TOTAL input rating of all appliances in the space (example: 150,000 Btu/h → 150 × 0.35 = 52.5 cfm; 35 cfm ÷ 0.35 = 100,000 Btu/h maximum input); each appliance must be interlocked with the air supply system (G2407.9.2) — G2407.9Combustion air delivered by the building's mechanical ventilation system
Total outdoor airflow = required ventilation air + combustion air at 0.35 cfm per 1,000 Btu/h (example: 60 cfm ventilation + (100 × 0.35 = 35 cfm) = 95 cfm) — G2407.9.3Gross opening size for louvers, grilles and screens
Gross opening = required net free area ÷ louver free-area percentage; use the known free area where known (44 ÷ 0.55 = 80 sq in); where design and free area are unknown use 25% for wood (60 ÷ 0.25 = 240 sq in) and 75% for metal (90 ÷ 0.75 = 120 sq in) — G2407.10Hydronic piping hydrostatic test pressure
Test at 1.5 × maximum system design pressure, but not less than 100 psi (example: 1.5 × 50 psi = 75 psi, so the 100 psi minimum governs); hold not less than 15 and not more than 20 minutes — M2101.10Installed insulation thickness of factory-made flexible air duct
Installed thickness = (actual outside diameter − nominal inside diameter) ÷ 2; nominal thickness is used for duct board and rigid ducts, and 75 percent of nominal (25-percent compression) for ductwrap — M1601.3, item 4