Master Plumber (UPC/IPC) — All Questions

A gas system serves a longest run of 80 ft to the most remote appliance, which needs 90 cfh. The table for 80 ft gives 3/4 in = 82 cfh and 1 in = 155 cfh. What size serves that final branch?

• a.1 in✓
• b.1-1/4 in
• c.1/2 in
• d.3/4 in

At the 80 ft longest length, 90 cfh exceeds the 82 cfh capacity of 3/4 in pipe, so 1 in (155 cfh) is required. In the longest-length method every section of the system is sized using the single longest run, not each section's own length. This conservative method avoids undersizing under worst-case simultaneous demand.IFGC §402.4

An appliance room contains a 120,000 BTU/hr furnace and a 40,000 BTU/hr water heater drawing combustion air from inside. Using the rule of 50 cubic feet of room volume per 1,000 BTU/hr for indoor air, what minimum room volume is required?

• a.8,000 ft^3✓
• b.12,000 ft^3
• c.16,000 ft^3
• d.4,000 ft^3

Total input = 120,000 + 40,000 = 160,000 BTU/hr, and at 50 ft^3 per 1,000 BTU/hr the room needs 160 x 50 = 8,000 ft^3. If the space is smaller than this, combustion air must be brought in from outdoors through sized openings. Adequate combustion air prevents oxygen depletion and dangerous incomplete combustion.IFGC §304.0

Combustion air is taken from outdoors using two openings, one high and one low. The rule is 1 square inch of free area per 4,000 BTU/hr for each opening when using direct outdoor openings. For a 200,000 BTU/hr appliance load, what is the minimum free area of each opening?

• a.50 in^2✓
• b.25 in^2
• c.40 in^2
• d.100 in^2

Each opening = load / 4,000 = 200,000 / 4,000 = 50 in^2 of free area. When two vertical (direct outdoor) openings are used, each is sized at 1 square inch per 4,000 BTU/hr, one within 12 in of the top and one within 12 in of the bottom. Louvers reduce free area, so gross opening size must be increased to compensate.IFGC §304.6

Appliance venting is classified by category. A Category I appliance is best described as which of the following?

• a.Positive vent pressure, condensing
• b.Negative vent pressure, non-condensing (draft hood or fan-assisted, standard flue)✓
• c.Negative vent pressure, condensing
• d.Positive vent pressure, non-condensing

A Category I appliance operates with a non-positive (negative) vent pressure and a non-condensing flue, so it uses a conventional type B vent or masonry chimney with natural or fan-assisted draft. Category IV is positive-pressure and condensing, requiring sealed plastic venting. Matching the vent material and pressure rating to the category is essential to avoid condensation damage or spillage.IFGC §503.0

A high-efficiency condensing furnace exhausts cool, wet flue gas under positive pressure. What venting category and material are appropriate?

• a.Category III, masonry chimney
• b.Category II, single-wall steel
• c.Category I, type B vent
• d.Category IV, listed PVC/CPVC sealed vent✓

A condensing furnace is Category IV, operating at positive vent pressure with condensing (wet, acidic) flue gas, and it requires a listed, sealed PVC or CPVC vent that resists corrosion and holds pressure. A type B vent or masonry chimney would corrode and leak flue products. The condensate must also be drained and often neutralized.IFGC §503.0

Corrugated stainless steel tubing (CSST) must be electrically bonded to reduce the risk of arcing from a lightning-induced surge. Where is the bonding clamp attached?

• a.To the appliance cabinet only
• b.To the gas meter body only
• c.To the CSST jacket only
• d.To a rigid pipe or CSST fitting ahead of the first downstream CSST, bonded to the grounding electrode system✓

CSST is bonded by clamping to a rigid gas pipe component or approved fitting and connecting to the building grounding electrode system, typically with a minimum 6 AWG copper conductor. Bonding drains induced energy so a lightning surge does not perforate the thin CSST wall by arcing. Standard equipment grounding alone does not satisfy the dedicated CSST bonding requirement.IFGC §310.0

A newly installed natural-gas piping system is pressure tested before being placed in service. A common test is 3 psi (or 1.5 times working pressure, whichever is greater) held for a set duration. For low-pressure residential piping, what is a typical minimum test pressure and duration?

• a.3 psi for at least 10 minutes with no pressure drop✓
• b.1 psi for 5 minutes
• c.10 psi for 30 seconds
• d.2 psi for 8 minutes

A common acceptance test for residential gas piping is 3 psi held for at least 10 minutes (some jurisdictions require longer) with no observable pressure drop on the gauge. The test isolates appliances and uses air or inert gas, never the fuel gas itself. Any drop indicates a leak that must be found and repaired before gas is introduced.IFGC §406.4

During a gas pressure test, appliances and their regulators must be protected. What is the correct way to include or exclude appliances during a 10 psi test?

• a.Leave appliances connected to save time
• b.Test only with the pilot lit
• c.Open all appliance valves fully
• d.Isolate or disconnect appliances and their regulators, which are not rated for the test pressure✓

Appliance regulators and controls are not rated for elevated test pressures, so appliances must be isolated by closing the individual appliance shutoff and disconnecting the appliance, or valving it off, before the piping is pressurized. Testing through an appliance can rupture its regulator diaphragm. Only the fixed piping is subjected to the test pressure.IFGC §406.0

A propane branch must deliver a 75,000 BTU/hr appliance at a longest length of 40 ft. Propane is 2,500 BTU/ft^3. The 40 ft table lists 1/2 in = 45 cfh and 3/4 in = 95 cfh. What is the required cfh and minimum pipe size?

• a.30 cfh, 1/2 in✓
• b.18 cfh, 1/2 in
• c.24 cfh, 1/2 in
• d.30 cfh, 3/4 in

cfh = 75,000 / 2,500 = 30 cfh, which is within the 45 cfh capacity of 1/2 in pipe at 40 ft, so 1/2 in is adequate. Because propane carries 2.5 times the energy per cubic foot of natural gas, the required cfh and pipe size are smaller for the same BTU load. Always convert BTU to cfh using the correct heating value for the fuel.IFGC §402.4

A hospital adds a nitrogen line for surgical tools alongside oxygen and medical air. What single feature most prevents a fatal mix-up of these medical/industrial gases at the outlet?

• a.Higher pressure
• b.Gas-specific (non-interchangeable) outlet and connector indexing, plus labeling✓
• c.Larger pipe
• d.Color-coded tape

Medical gas station outlets use gas-specific, non-interchangeable indexing so a nitrogen connector cannot fit an oxygen outlet, backed by permanent labeling and color coding. The physical keying, not the label alone, is the primary defense against a lethal wrong-gas connection. A crossover test at commissioning confirms each outlet delivers only its intended gas.NFPA 99

A gas piping system must include a sediment trap (drip leg) ahead of certain appliances. What is the purpose and typical location of the drip leg?

• a.To vent gas, at the appliance
• b.To bond the pipe, at the regulator
• c.To catch moisture and debris before it enters the appliance control, downstream of the appliance shutoff✓
• d.To reduce pressure, at the meter

A sediment trap is a capped tee installed downstream of the appliance shutoff and ahead of the appliance control so moisture, scale, and debris drop into the leg instead of fouling the gas valve. It is required at most appliances except those specifically exempt such as ranges and clothes dryers in some codes. The leg must be accessible for cleaning.IFGC §408.0

Each gas appliance must have an accessible manual shutoff. Where must the appliance shutoff valve be located?

• a.In the same room, within 6 ft of the appliance, upstream of the union and appliance connector✓
• b.Anywhere in the building
• c.Inside the appliance cabinet
• d.At the meter only

The appliance shutoff must be in the same room as the appliance and within 6 ft of it, located upstream of the flexible connector and union so the appliance can be isolated for service. Placing it only at the meter would require shutting off the whole building. Accessibility without tools is required for emergencies.IFGC §409.0

Using the known-air-infiltration method, an appliance space of 10,000 ft^3 is credited with 0.35 air changes per hour of natural infiltration. How many cubic feet of infiltration air per hour does the space provide?

• a.350 cfh
• b.35,000 cfh
• c.1,750 cfh
• d.3,500 cfh✓

Infiltration air = volume x air changes per hour = 10,000 x 0.35 = 3,500 cubic feet per hour. This method credits only the air that leaks through a standard building, which in a tight modern house is often too little for the appliance load. When it is insufficient, dedicated outdoor combustion air must be supplied.IFGC §304.5

A gas appliance vent connector runs 12 ft horizontally to the chimney. Code requires a minimum upward rise of 1/4 in per foot toward the chimney. What total vertical rise must the connector have?

• a.12 in
• b.1-1/2 in
• c.6 in
• d.3 in✓

Rise = 1/4 in per ft x 12 ft = 3 in of upward slope from the appliance to the chimney. The rise keeps hot flue gas moving upward and prevents it from stalling and spilling back into the room. A level or downward-sloped connector defeats natural draft and can spill carbon monoxide.IFGC §503.6

A two-appliance system: appliance A needs 60 cfh and appliance B needs 40 cfh. Using the longest-length method, the section of pipe between the meter and the first tee carries what demand?

• a.40 cfh
• b.100 cfh✓
• c.60 cfh
• d.20 cfh

The common section upstream of the first tee carries the sum of all downstream demand, 60 + 40 = 100 cfh, and is sized for that total at the system's longest length. Each branch downstream of the tee is then sized for only the appliance it serves. Undersizing the common section starves both appliances during simultaneous use.IFGC §402.4

A leak test on an in-service gas line uses a soap-bubble or electronic method rather than a pressure drop. When is the bubble/electronic leak check the appropriate method?

• a.On new rough piping before drywall
• b.Never on natural gas
• c.On existing pressurized piping and appliance connections that cannot be depressurized for a formal test✓
• d.Only on propane tanks

A leak-detection solution or electronic sniffer is used to check joints and connections on piping and appliances that are already in service and under normal operating pressure, where a formal pressure-drop test is impractical. Bubbles at a joint reveal an escaping leak for immediate repair. A never open flame is used to check for gas leaks.IFGC §406.4

An elevated industrial gas line operates at 5 psi and is regulated down for appliances rated in inches of water column. Using 1 psi = 27.7 in water column, what is 5 psi expressed in inches of water column?

• a.138.5 in w.c.✓
• b.55.4 in w.c.
• c.27.7 in w.c.
• d.500 in w.c.

Inches of water column = psi x 27.7 = 5 x 27.7 = 138.5 in w.c. Appliance regulators are commonly set near 7 in w.c. for natural gas, so an elevated 138.5 in w.c. supply must be stepped down by a line-pressure regulator with overpressure protection. Mixing up psi and inches of water column is a common and dangerous error.IFGC §614.0

A natural-gas dryer needs 35,000 BTU/hr and a range needs 65,000 BTU/hr on a shared branch. Using 1,000 BTU/ft^3, what is the combined cfh the common branch must carry?

• a.35 cfh
• b.1,000 cfh
• c.65 cfh
• d.100 cfh✓

Combined input = 35,000 + 65,000 = 100,000 BTU/hr, and at 1,000 BTU per cubic foot that is 100 cfh on the shared branch. The common section always carries the sum of the downstream appliance demands. Each appliance's own connector is then sized for only its individual load.IFGC §402.4

A natural-gas furnace is rated at 80,000 BTU/hr. Using a heating value of 1,000 BTU per cubic foot, what gas volume flow must the piping deliver?

• a.80 cfh✓
• b.8 cfh
• c.800 cfh, because you multiply the input by ten
• d.40 cfh, taking half the rated input

cfh = BTU/hr divided by heating value = 80,000 / 1,000 = 80 cfh. Per IFGC 402.4, gas piping is sized in cubic feet per hour, and for natural gas at ~1,000 BTU/ft^3 the cfh equals the input in thousands of BTU. This cfh is carried into the sizing table at the system's longest length.IFGC §402.4

A 50,000 BTU/hr natural-gas water heater is served on its own branch. At 1,000 BTU per cubic foot, what is the required gas flow?

• a.5 cfh, dividing the input by ten thousand
• b.500 cfh, moving the decimal the wrong way
• c.25 cfh, using half the rated input
• d.50 cfh✓

cfh = 50,000 / 1,000 = 50 cfh. IFGC 402.4 sizes each branch for the demand of the appliance it serves, expressed in cfh. The branch to a single water heater carries only that appliance's 50 cfh, while the common section upstream carries the sum of all appliances.IFGC §402.4

A propane pool heater is rated at 200,000 BTU/hr. Propane has a heating value of about 2,500 BTU per cubic foot. What gas flow in cfh must the piping deliver?

• a.200 cfh, using 1,000 BTU per cubic foot instead of 2,500
• b.80 cfh✓
• c.40 cfh, taking half of the correct value
• d.500 cfh, multiplying instead of dividing

cfh = 200,000 / 2,500 = 80 cfh. IFGC 402.4 requires using the correct heating value for the fuel; propane carries about 2,500 BTU/ft^3, roughly 2.5 times natural gas, so the cfh is much lower for the same input. Using 1,000 BTU/ft^3 wrongly inflates the flow to 200 cfh.IFGC §402.4

The standard natural-gas pipe sizing tables in the fuel gas code are published for one assumed gas specific gravity. What specific gravity do those tables assume?

• a.1.52
• b.0.35, a value lighter than any fuel gas used
• c.0.60✓
• d.1.00

IFGC Table 402.4(1) and related tables are based on a natural-gas specific gravity of 0.60. When the actual gas differs, a multiplier from the code adjusts the capacity. Propane tables use a different gravity (about 1.52), so the correct table must match the fuel.IFGC Table 402.4

Liquefied petroleum (propane) gas is heavier than air. Because of this property, where does an LP-gas leak tend to accumulate?

• a.Near the ceiling, because it rises the way natural gas does
• b.It disperses evenly through the room and never collects
• c.It vents itself harmlessly to the outdoors on its own
• d.In low areas such as floors and pits✓

Propane has a specific gravity of about 1.52, so it is heavier than air and settles into low spots like floors, crawl spaces, and pits, per NFPA 58 and IFGC hazard provisions. This is why LP appliances have low-level ignition concerns and LP is not stored below grade without special provisions.IFGC §404

A residential natural-gas appliance operates at a typical delivered inlet pressure. What is that common supply pressure?

• a.About 2 psi measured right at the burner orifice
• b.About 14 inches of water column at the appliance inlet
• c.About 7 inches of water column✓
• d.About 11 inches of water column, which is the propane value

Natural-gas appliances are typically supplied at about 7 in w.c. (with a manifold pressure near 3.5 in w.c.), per IFGC and NFPA 54 appliance data. Propane appliances instead use about 11 in w.c. Matching the delivered pressure to the appliance rating is essential for correct combustion.IFGC §410.3

A propane appliance is set for the fuel it burns. What is the typical delivered inlet supply pressure for a propane appliance?

• a.About 2 psi delivered directly at the appliance inlet
• b.About 7 inches of water column, which is the natural-gas value
• c.About 11 inches of water column✓
• d.About 3.5 inches of water column at the manifold outlet

Propane appliances are commonly supplied at about 11 in w.c., higher than natural gas at about 7 in w.c., per NFPA 54/58 appliance data. The second-stage regulator on an LP system delivers this pressure. Using natural-gas pressure on a propane appliance would underfire it.IFGC §410.3

A gas line operates at 11 inches of water column. Using 1 psi = 27.7 inches of water column, what is 11 in w.c. expressed in psi?

• a.4.0 psi, off by a full factor of ten
• b.3.05 psi, multiplying by 27.7 instead of dividing
• c.0.30 psi, using the wrong conversion constant
• d.0.40 psi✓

psi = in w.c. divided by 27.7 = 11 / 27.7 = 0.397, about 0.40 psi. IFGC recognizes that residential appliance pressures are fractions of a psi, which is why low-pressure systems are measured in inches of water column. Confusing the two units is a common and dangerous sizing error.IFGC §406

Low-pressure natural-gas sizing tables are built around a specified allowable pressure drop across the piping. What pressure drop do the common low-pressure tables assume?

• a.0.3 psi, an elevated-pressure design assumption
• b.3 inches of water column across the whole system
• c.1.0 psi, which is a high-pressure design value
• d.0.5 inch of water column✓

The standard low-pressure sizing tables in IFGC Table 402.4(1) are based on a 0.5 in w.c. pressure drop. A larger allowable drop (a separate table) permits smaller pipe. The design must not exceed the drop the appliance can tolerate while still delivering its rated input.IFGC Table 402.4

A gas system has four outlets; the most remote outlet is 70 ft from the meter. Under the longest-length method, what length sizes the section of pipe closest to the meter?

• a.70 ft (the single longest run)✓
• b.The physical length of that section of pipe only
• c.The average of all four outlet run lengths combined
• d.The length of the run to the nearest outlet

The longest-length (or 'longest run') method in IFGC 402.4 sizes every section of the system using the single longest run from the meter to the most remote outlet. This conservative approach guards against undersizing under simultaneous demand. Each section's own physical length is not used in this method.IFGC §402.4

A gas branch must carry 120 cfh at a longest length of 50 ft. The table at 50 ft lists 3/4 in = 99 cfh and 1 in = 190 cfh. What is the minimum pipe size?

• a.1 in✓
• b.1/2 in
• c.3/4 in
• d.1-1/4 in

The 120 cfh demand exceeds the 99 cfh capacity of 3/4 in pipe at 50 ft, so the next size, 1 in (190 cfh), is required, per IFGC Table 402.4. Gas pipe is chosen as the smallest size whose table capacity at the longest length equals or exceeds the demand. A 3/4 in pipe would be overloaded.IFGC Table 402.4

A common section of pipe upstream of the first tee feeds a furnace (80 cfh), a water heater (45 cfh), and a clothes dryer (25 cfh). What demand must that common section carry?

• a.25 cfh, counting only the last appliance on the run
• b.80 cfh, counting only the single largest appliance
• c.125 cfh, leaving out the clothes dryer load
• d.150 cfh✓

The common section carries the sum of all downstream demands: 80 + 45 + 25 = 150 cfh, per IFGC 402.4. Each branch downstream of a tee is sized for only the appliance it serves, but every upstream section must carry the total it feeds. Undersizing the common run starves all appliances at once.IFGC §402.4

What is the primary consequence of undersizing fuel-gas piping so it cannot deliver the required cfh?

• a.Pressure drop starves the appliance✓
• b.Higher gas velocity always improves the appliance performance
• c.The appliance receives too much pressure and dangerously over-fires
• d.Nothing happens, because the appliances self-compensate for it

Undersized gas pipe produces excessive pressure drop, so the appliance cannot draw its rated cfh, leading to a low firing rate and incomplete combustion that generates carbon monoxide, per IFGC 402.4 sizing intent. Correct sizing keeps the delivered pressure within the appliance's operating range under full demand.IFGC §402.4

Corrugated stainless steel tubing (CSST) is not sized from the standard steel-pipe schedule tables. How is CSST capacity determined?

• a.It does not require any sizing because it is flexible
• b.From the manufacturer's listed EHD tables✓
• c.From standard copper-tube sizing tables in the fuel gas code
• d.From Schedule 40 black-steel tables using the nominal pipe size

CSST is sized using the manufacturer's listed capacity tables keyed to the product's equivalent hydraulic diameter (EHD), not the generic steel tables, per IFGC 402.4 and the listing. Because CSST's inside geometry differs from threaded pipe, only the listed data gives correct capacity. Substituting steel tables can undersize it.IFGC §402.4

Polyethylene (PE) gas pipe is commonly used for underground fuel-gas service. How must it be handled where it comes above grade?

• a.It may be left exposed above grade as long as it is painted
• b.Transition to metallic pipe below grade with an anodeless riser✓
• c.It may be run above grade and continue inside the building freely
• d.It is prohibited underground and may only be used indoors instead

PE gas pipe is approved for underground use but degrades under sunlight and physical exposure, so IFGC 404 requires an anodeless riser transitioning to metallic pipe below grade before it emerges. PE is not permitted inside buildings or exposed above grade. Tracer wire is installed with it for locating.IFGC §404.4

Which material is NOT permitted for interior fuel-gas distribution piping?

• a.Copper tube where the gas has low hydrogen sulfide content
• b.Corrugated stainless steel tubing that is listed for gas
• c.PVC plastic pipe✓
• d.Black steel pipe joined with threaded fittings

PVC is not an approved fuel-gas piping material for interior distribution under IFGC 403; approved materials include steel, CSST, and (for low-H2S gas) copper. PVC and other thermoplastics lack the required fire and pressure ratings indoors. PE is limited to underground service only.IFGC §403

Copper tube is allowed for natural gas only under a specific gas-quality condition. What is that condition?

• a.Copper is never allowed for natural gas under any circumstances
• b.Hydrogen sulfide below 0.3 grains per 100 scf✓
• c.Copper is allowed only for propane service and never for gas
• d.Copper is always allowed for any natural gas without restriction

IFGC 403.4 permits copper for natural gas only where the gas is not corrosive, generally less than 0.3 grains of hydrogen sulfide per 100 scf; sulfur compounds attack copper and form scale. The local gas utility can confirm gas quality. Where H2S is higher, steel or CSST is used instead.IFGC §403.4

Thread sealant used on fuel-gas pipe joints must meet a specific requirement. What is it?

• a.An oil-based sealant is the preferred product for gas threads
• b.Any general-purpose pipe dope from the shelf is acceptable to use
• c.It must be resistant to the gas (LP-gas resistant on propane)✓
• d.No sealant of any kind may be used on fuel-gas threaded joints

IFGC 403.10 requires joint compounds and tape to be resistant to the fuel gas, and specifically LP-gas resistant on propane systems, so the sealant is not dissolved or degraded. Ordinary sealants can soften in the presence of gas and cause leaks. The sealant is applied to male threads only.IFGC §403.10

A flexible appliance connector joins fixed gas piping to a movable appliance. What installation limit applies?

• a.It may pass through a wall as long as it is sleeved for protection
• b.It may be permanently concealed behind or under the appliance
• c.Its overall length is unlimited for any size of appliance served
• d.It must not pass through walls, floors, or concealed spaces✓

IFGC 411.1 prohibits a listed flexible appliance connector from passing through walls, floors, ceilings, or any concealed location, and limits its length; it must serve a single appliance and remain in the same room, accessible. Concealing or extending a connector creates an unseen leak risk.IFGC §411.1

A ground-joint union lets an appliance be disconnected for service. Where is the union placed relative to the appliance shutoff valve?

• a.Downstream of the shutoff, between the valve and appliance✓
• b.No union is permitted anywhere at a gas appliance connection
• c.At the gas meter, so the whole building can be isolated first
• d.Upstream of the shutoff valve, on the supply side of the piping

The union is installed downstream of the appliance shutoff so the valve can isolate gas before the union is broken to remove the appliance, per IFGC 409/411 practice. This lets the appliance be disconnected without shutting the whole system. A union upstream of the valve would leak gas when opened.IFGC §411

May fuel-gas piping be used as the grounding electrode for the building electrical system?

• a.Yes, but only when it is used for lightning-protection grounding
• b.No; gas piping must not be a grounding electrode✓
• c.Yes, and it is required to serve as the building's primary ground
• d.Yes, because it makes an excellent low-resistance primary ground

Fuel-gas piping must not serve as a grounding electrode, per IFGC 310 and the NEC; a fault current on gas pipe could arc and perforate it. CSST additionally requires dedicated bonding to the grounding electrode system to drain induced surges. Grounding electrodes are ground rods, water pipe, and building steel.IFGC §310 / NEC

Combustion air is provided by a single permanent opening communicating with the outdoors. What free-area rule sizes that opening?

• a.1 in^2 per 3,000 BTU/hr of input✓
• b.1 in^2 per 4,000 BTU/hr, the vertical two-opening duct ratio
• c.1 in^2 per 1,000 BTU/hr, which greatly oversizes the opening
• d.1 in^2 per 50 BTU/hr of aggregate appliance input

IFGC 304.6.1 sizes a single combustion-air opening at 1 in^2 per 3,000 BTU/hr of aggregate input, minimum 100 in^2, located within 12 in of the ceiling and communicating with the outdoors. Two-opening and ducted methods use different ratios. Adequate combustion air prevents oxygen depletion and CO.IFGC §304.6.1

When two combustion-air openings connect to the outdoors through horizontal ducts, what free-area ratio sizes each opening?

• a.1 in^2 per 4,000 BTU/hr, which is the vertical-duct ratio
• b.1 in^2 per 1,000 BTU/hr, which oversizes the ducted opening
• c.1 in^2 per 2,000 BTU/hr✓
• d.1 in^2 per 3,000 BTU/hr, the single-opening direct ratio

For two openings communicating with the outdoors through horizontal ducts, IFGC 304.6 requires 1 in^2 of free area per 2,000 BTU/hr for each opening. Vertical ducts use 1 in^2 per 4,000 BTU/hr because a vertical duct promotes flow. The high opening supplies dilution and the low opening supplies combustion air.IFGC §304.6

A single outdoor combustion-air opening serves a 150,000 BTU/hr load at 1 in^2 per 3,000 BTU/hr. What free area does the calculation give?

• a.100 in^2, doubling the correct result
• b.75 in^2, using the wrong 2,000 BTU ratio
• c.30 in^2, dividing by 5,000 by mistake
• d.50 in^2✓

Free area = 150,000 / 3,000 = 50 in^2, per IFGC 304.6.1, though the 100 in^2 minimum for a single opening would then govern. The calculation itself yields 50 in^2; the code floor raises small results. Louvers further reduce net free area and must be compensated for.IFGC §304.6.1

Two vertical combustion-air ducts serve a 240,000 BTU/hr load at 1 in^2 per 4,000 BTU/hr each. What is the free area of each opening?

• a.60 in^2✓
• b.30 in^2, dividing the load by 8,000 instead of 4,000
• c.48 in^2, using a 5,000 BTU per square inch ratio
• d.120 in^2, using the 2,000 BTU horizontal ratio by mistake

Each vertical opening = 240,000 / 4,000 = 60 in^2, per IFGC 304.6. Vertical ducts use the 4,000 ratio because they draft more effectively than horizontal ducts, which use 2,000. One opening is placed high and one low so both dilution and combustion air are supplied.IFGC §304.6

A required net free area of 50 in^2 must pass through a wood louver that is about 25 percent free area. What gross louver opening is required?

• a.200 in^2✓
• b.50 in^2, ignoring the blockage of the louver blades
• c.67 in^2, using a metal-louver 75 percent free-area factor
• d.100 in^2, correcting for only half of the louver blockage

Gross opening = required net area / louver free fraction = 50 / 0.25 = 200 in^2, per IFGC 304.6. Wood louvers are assumed about 25 percent free and metal louvers about 75 percent unless labeled otherwise. Failing to correct for louver blockage leaves the appliance short of combustion air.IFGC §304.6

A Category I gas appliance uses which type of venting?

• a.No vent at all, because Category I appliances are unvented
• b.A Type B gas vent or a lined masonry chimney✓
• c.A sealed PVC vent designed for positive pressure and condensate
• d.A bare single-wall aluminum vent with no clearance to combustibles

A Category I appliance vents with non-positive pressure and non-condensing flue gas, so IFGC 503 allows a Type B gas vent or an approved lined chimney. Condensing (Category IV) appliances instead require sealed plastic venting. Matching the vent to the appliance category prevents condensation damage and spillage.IFGC §503

A single-wall metal vent connector runs from a gas appliance toward the chimney. What minimum clearance to combustibles is required?

• a.6 in✓
• b.0 in, since a metal connector may touch wood framing
• c.1 in, which applies only to a listed double-wall connector
• d.18 in, which is far more than the code requires here

A single-wall metal vent connector requires 6 in of clearance to combustibles, per IFGC 503.10.6, because its outer surface runs hot. Type B double-wall connectors allow reduced clearance (often 1 in) due to their air space. Reduced clearance requires a listed connector, not single-wall pipe.IFGC §503.10.6

For a naturally drafting appliance, the horizontal length of a single-wall vent connector is limited relative to the vent height. What is that limit?

• a.No more than 75 percent of the vent height✓
• b.It may be as much as twice the vertical vent height allowed
• c.It may equal the full vertical height of the chimney or vent
• d.There is no length limit on a horizontal vent connector

IFGC 503.10 limits a single-wall vent connector's horizontal run to 75 percent of the vent or chimney height (Type B connectors allow 100 percent). A long horizontal connector cools the flue gas and robs draft. The connector must also rise toward the chimney to keep gases moving upward.IFGC §503.10

With all appliances operating, a plumber checks the draft hood for spillage. What is being verified?

• a.That flue gases draft up the vent instead of spilling into the room✓
• b.That the vent connector is completely sealed and airtight
• c.That the pilot flame has been extinguished before testing
• d.That the appliance gas valve is fully closed during the test

A spillage (backdraft) test at the draft-hood relief opening, per IFGC 503, confirms the vent is establishing draft and not dumping combustion products into the room. Spillage indicates blockage, undersized venting, or depressurization. Persistent spillage releases carbon monoxide and must be corrected.IFGC §503

A Type B gas vent penetrates and terminates above a roof. What minimum termination height above the roof is required at the penetration?

• a.Below the ridge line so it is hidden from view
• b.6 in above the roof, which is below the code minimum
• c.At least 1 ft above the roof✓
• d.Flush with the roof surface at the point of penetration

IFGC 503.6.4 requires a gas vent to terminate at least 1 ft above the roof it penetrates, with more height on steeper pitches, and clear of nearby walls and openings, using a listed cap. Terminating too low invites downdraft and re-entry of flue gases. Exact height comes from the vent-height chart.IFGC §503.6.4

A direct-vent (sealed-combustion) appliance is installed in a small utility room. What combustion-air requirement applies?

• a.It draws its combustion air from the surrounding room space
• b.None from the room; air comes from outdoors through its sealed intake✓
• c.It needs 50 ft^3 of room volume per 1,000 BTU/hr of input
• d.It requires a lined masonry chimney for its combustion air

A direct-vent appliance is sealed to the room and draws combustion air directly from outdoors through a concentric or separate intake, so IFGC 503 requires no room combustion-air openings. This makes it suitable for tight or confined spaces. Its exhaust also terminates outdoors per the listing.IFGC §503

CSST that requires bonding is connected to the grounding electrode system with a bonding jumper. What is the minimum size of that conductor?

• a.14 AWG copper, which is far too small for the bonding jumper
• b.6 AWG copper✓
• c.No bonding conductor is required for corrugated stainless tubing
• d.10 AWG copper, smaller than the code-required minimum size

CSST bonding uses a conductor not smaller than 6 AWG copper, clamped to a rigid metallic gas component and connected to the grounding electrode system, per IFGC 310.1.1 and the manufacturer's instructions. The heavy conductor drains induced lightning energy so a surge cannot arc through and perforate the thin CSST wall.IFGC §310.1.1

A commercial gas train has a component that automatically stops gas flow if the flame is lost. What is that component?

• a.A vacuum breaker installed on the appliance connector
• b.An automatic safety shutoff valve✓
• c.A simple swing check valve on the appliance supply line
• d.A thermal expansion tank connected to the gas manifold

A commercial gas train includes an automatic safety shutoff valve driven by a flame-safeguard/flame-sensing control that closes on flame failure, per NFPA 54. This prevents raw gas from accumulating when ignition is lost. The train also typically includes manual valves, a regulator, and pressure switches in a defined order.NFPA 54

A commercial gas train has switches that shut the appliance down when supply pressure is outside safe limits. What are these devices?

• a.A temperature-only switch mounted on the appliance cabinet
• b.No such devices exist on a commercial appliance gas train
• c.High- and low-gas-pressure switches✓
• d.A flow meter that records the appliance's gas consumption

High- and low-gas-pressure switches on a commercial gas train, per NFPA 54, prevent firing when supply pressure is too high (risking overfire) or too low (risking incomplete combustion). They are interlocked with the burner control so an out-of-range condition locks out ignition until corrected.NFPA 54

A line-pressure regulator has an atmospheric vent connection. How must that vent terminate?

• a.Capped tightly so that no gas can ever escape from the vent
• b.Into the appliance flue so a leak is carried up the chimney
• c.Inside the equipment room near the regulator for easy access
• d.Outdoors, protected by an insect screen✓

A gas regulator's atmospheric vent must terminate outdoors and be screened against insects, per IFGC 410.3, so a ruptured diaphragm releases gas safely outside. A vent-limiting device may be used where permitted. Capping the vent would prevent the regulator from breathing and operating.IFGC §410.3

When downstream piping and appliances could see pressure exceeding their rating, what protection does the code require?

• a.No protection is required if the regulator looks new
• b.A relief valve that is piped down to the building sanitary sewer
• c.Overpressure protection✓
• d.Only a thermal expansion tank on the gas manifold assembly

IFGC 410.1 requires overpressure protection wherever a regulator failure could subject appliances to pressure above their rating, using relief valves, a monitoring regulator, or a series-regulator arrangement. This protects appliance controls not rated for elevated pressure. Elevated-pressure systems always include such protection.IFGC §410.1

An elevated-pressure (2 psi) gas system serves a dwelling. How is appliance pressure managed?

• a.No regulator is needed because appliances accept any inlet pressure
• b.Only commercial buildings are ever allowed to run at 2 psi service
• c.Elevated pressure is never permitted in a dwelling under any code
• d.A line regulator with overpressure protection reduces it near the appliances✓

IFGC 402.6 permits elevated-pressure (for example 2 psi) systems in dwellings when a line-pressure regulator with overpressure protection reduces the pressure to the appliance's rating near the appliances. The higher trunk pressure lets smaller pipe carry the load; the regulator delivers safe appliance pressure downstream.IFGC §402.6

Compared with the standard 0.5 in w.c. low-pressure table, a 2 psi sizing table lets a given pipe carry how much gas?

• a.More gas✓
• b.Less gas than the low-pressure table for the same pipe size
• c.Exactly the same capacity, since pressure does not affect flow
• d.No gas at all, because 2 psi sizing tables are not published

Because a 2 psi system tolerates a much larger pressure drop than a 0.5 in w.c. system, IFGC 402.4 sizing shows the same pipe carrying more gas (or a smaller pipe serving the same load). This is the advantage of elevated-pressure distribution, paired with a downstream regulator to protect appliances.IFGC §402.4

A 250-gallon aboveground ASME propane container is set beside a dwelling. What minimum separation from the building is required?

• a.25 ft
• b.10 ft✓
• c.3 ft, essentially placing the tank against the building wall
• d.5 ft

NFPA 58 requires an aboveground ASME propane container in the 125 to 500 gallon range to be at least 10 ft from a building and from the line of adjoining property that may be built upon. The separation limits fire exposure and allows for relief-valve discharge. Larger tanks require greater distances.NFPA 58

How must portable DOT propane cylinders (such as 20 lb grill cylinders) be stored?

• a.Outdoors or in approved locations, not inside occupied buildings✓
• b.In an attic space above the living area of the dwelling
• c.Anywhere indoors is acceptable as long as it is convenient
• d.In an occupied basement close to the appliance being served

NFPA 58 prohibits storing DOT propane cylinders inside occupied buildings; because propane is heavier than air, a leak in a basement or interior room can pool and reach an ignition source. Cylinders are stored outdoors, upright, and secured. Only very limited quantities are allowed indoors under strict conditions.NFPA 58

How must the relief valve on an aboveground propane container be arranged?

• a.Capped tightly so that pressure can never be released at all
• b.Discharging downward toward grade beneath the storage tank
• c.Venting horizontally into the adjacent building through the wall
• d.Discharging vertically upward and unobstructed✓

NFPA 58 requires a container relief valve to discharge vertically upward and remain unobstructed (with a rain cap that does not restrict flow), so an overpressure release disperses safely away from people and structures. Capping or obstructing the valve defeats the tank's primary safety device and can cause a BLEVE.NFPA 58

After pressure testing, a new gas line must be purged before service. How is purging performed?

• a.Purge with an appliance pilot lit so the air is burned off
• b.No purge is needed once the pressure test has been passed
• c.Purge to the outdoors, away from ignition sources✓
• d.Purge the air into the room to finish the job more quickly

IFGC 406.6 requires purging piping to a safe point of discharge outdoors, away from ignition sources and not into a confined space, when placing gas in service. Purging into a room can create a flammable mixture. No open flame or ignition source is permitted during the operation.IFGC §406.6

Fuel gas is odorized so leaks can be detected. What is added for this purpose?

• a.A visible dye that colors the gas as it leaks from a joint
• b.An odorant such as mercaptan✓
• c.Chlorine, to give it a sharp detectable chemical smell
• d.Nothing; both natural gas and propane are naturally pungent

IFGC 401.6 requires fuel gas to contain an odorant, commonly a mercaptan, giving the characteristic rotten-egg smell so leaks are detectable before reaching a hazardous concentration. Natural gas and propane are otherwise odorless. Odor fade in some soils is why electronic detection is also used underground.IFGC §401.6

What is the maximum support spacing for 3/4 in horizontal steel gas pipe?

• a.4 ft
• b.6 ft
• c.8 ft✓
• d.10 ft

IFGC Table 415.1 lists 8 ft maximum spacing for 3/4 in and 1 in horizontal steel gas pipe (1/2 in is 6 ft; 1-1/4 in and larger is 10 ft). Proper support prevents sag that could trap condensate or stress joints. Vertical piping is supported at each floor level.IFGC §415.1

Underground metallic gas piping is in contact with the soil. What corrosion requirement applies?

• a.No corrosion protection is required for buried metallic gas pipe
• b.Bare steel needs no protection at all when buried underground
• c.It must be protected by coating, wrapping, or cathodic protection✓
• d.Galvanizing alone always suffices with no other corrosion measures

IFGC 404 requires underground metallic gas pipe to be protected from corrosion with coatings, wrapping, or cathodic protection, because soil moisture attacks buried steel. Tracer wire is also installed with nonmetallic pipe for locating. Unprotected buried metal can corrode through and leak.IFGC §404.11

Where fuel-gas piping passes through a masonry or concrete foundation wall, what installation is required?

• a.It must be grouted solidly into the concrete foundation wall
• b.Gas piping is never permitted to pass through a foundation wall
• c.No protection is needed where the pipe crosses the foundation
• d.It must be sleeved and protected from settlement✓

IFGC 404.7 requires gas piping penetrating a foundation to be sleeved and protected so wall movement or settlement does not shear the pipe. Solidly grouting the pipe transfers building movement directly to it. The annular space is sealed to keep out water and gas migration.IFGC §404.7

Fuel-gas piping is prohibited in certain concealed and mechanical locations. Which is a prohibited location?

• a.Exposed along a basement joist with proper support and clearance
• b.Inside an air-supply duct or plenum✓
• c.In an accessible, ventilated mechanical equipment room
• d.In a ventilated attic when it is properly supported and protected

IFGC 404 prohibits gas piping in air-supply ducts, plenums, clothes and dumbwaiter chutes, chimneys, and vents, because a leak into moving air or a flue is extremely hazardous. Piping is routed in accessible or properly protected spaces instead. Piping in solid partitions is likewise restricted.IFGC §404.4

An appliance set up for natural gas is to be connected to a propane supply. What is required?

• a.Convert the appliance (orifices and regulator) for propane first✓
• b.The two fuels are freely interchangeable with no conversion at all
• c.Only the regulator, and never the orifices, needs to be changed out
• d.No change is ever needed when switching between the two fuels

Natural gas and propane have different heating values and pressures, so NFPA 54 requires an appliance to be converted with the manufacturer's orifice and regulator kit before switching fuels. Running a natural-gas appliance on unconverted propane greatly overfires it, producing soot and carbon monoxide.NFPA 54

A sediment trap is required ahead of many appliances but is exempt for certain ones. Which appliances are commonly exempt?

• a.Furnaces, which are the largest gas appliance in the dwelling
• b.Ranges, clothes dryers, and illuminating appliances✓
• c.No appliance is ever exempt from the sediment-trap requirement
• d.Water heaters, because their gas valve is close to the floor

IFGC 408.4 requires a sediment trap ahead of the appliance control but exempts ranges, clothes dryers, outdoor grills, gas lights, and similar illuminating/decorative appliances. Furnaces and water heaters must have the trap. The trap catches moisture and debris before the gas valve and must remain accessible.IFGC §408.4

A residential gas system is pressure tested at 3 psi. What test gauge should be used?

• a.No gauge; a soap-bubble check alone is the acceptance test
• b.Any gauge at all, regardless of its range or the graduations
• c.One fine enough to detect a small pressure drop✓
• d.A gauge reading only in coarse 5 psi increments across its dial

IFGC 406.1 requires a test gauge appropriate to the test pressure so a small leak-induced drop is visible; a coarse gauge could hide a slow leak. For a low-pressure 3 psi test, a gauge reading in fine increments (or a manometer) is used. The reading must hold with no drop for the required duration.IFGC §406.1

A commercial boiler is rated at 400,000 BTU/hr on natural gas at 1,000 BTU per cubic foot. What gas flow must the piping deliver?

• a.400 cfh✓
• b.200 cfh, mistakenly taking half of the rated input
• c.40 cfh, off by a full factor of ten in the division
• d.4,000 cfh, multiplying by ten instead of dividing

cfh = 400,000 / 1,000 = 400 cfh, per IFGC 402.4. Large commercial appliances drive substantial cfh demand that sizes the branch and often the whole service. This cfh is carried into the sizing table at the system's longest length to select the pipe size.IFGC §402.4

A six-outlet gas system is sized. The single longest run from the meter to any outlet is 95 ft. Under the longest-length method, which length governs every section?

• a.The sum of all the individual outlet run lengths added together
• b.Zero, because run length is not used in fuel-gas sizing at all
• c.The length of the run to the nearest outlet on the system
• d.95 ft✓

Under the longest-length method in IFGC 402.4, the single longest run (95 ft) is used to enter the sizing table for every section of the system. This conservative approach avoids undersizing when multiple appliances fire together. Individual section lengths are not summed or averaged in this method.IFGC §402.4

A whole house has appliances totaling 275,000 BTU/hr on natural gas at 1,000 BTU per cubic foot. What total cfh must the meter and main serve?

• a.275 cfh✓
• b.137 cfh, mistakenly taking half of the total connected input
• c.2,750 cfh, multiplying by ten rather than dividing by 1,000
• d.27.5 cfh, off by a full factor of ten in the division

Total demand = 275,000 / 1,000 = 275 cfh, per IFGC 402.4. The whole-house demand sizes the meter and the main from the meter to the first tee. Individual branches downstream are then sized for only the appliances each serves.IFGC §402.4

A new residential gas line is tested with air, not the fuel gas itself. Why is air (or an inert gas) used as the test medium?

• a.Because using fuel gas as the test medium costs more money
• b.Because the fuel gas would damage the test gauge diaphragm
• c.To avoid a flammable mixture during testing✓
• d.Because air is heavier than gas and finds leaks more reliably

IFGC 406 requires the pressure test to use air, nitrogen, carbon dioxide, or another inert gas, never the fuel gas, so no flammable mixture is created in the piping under test. Appliances are isolated because their regulators are not rated for the test pressure. Any pressure drop indicates a leak to repair.IFGC §406.4