CSLB General Building (B) — 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.1/2 in
• b.3/4 in
• c.1 in✓
• d.1-1/4 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.4,000 ft^3
• b.12,000 ft^3
• c.16,000 ft^3
• d.8,000 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, non-condensing
• b.Negative vent pressure, non-condensing (draft hood or fan-assisted, standard flue)✓
• c.Positive vent pressure, condensing
• d.Negative vent pressure, 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 I, type B vent
• b.Category II, single-wall steel
• c.Category IV, listed PVC/CPVC sealed vent✓
• d.Category III, masonry chimney

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 CSST jacket only
• b.To the appliance cabinet only
• c.To the gas meter body 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.2 psi for 8 minutes
• d.10 psi for 30 seconds

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

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.18 cfh, 1/2 in
• b.24 cfh, 1/2 in
• c.30 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.Color-coded tape
• b.Larger pipe
• c.Higher pressure
• d.Gas-specific (non-interchangeable) outlet and connector indexing, plus labeling✓

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

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

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.1,750 cfh
• c.3,500 cfh✓
• d.35,000 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.1-1/2 in
• b.6 in
• c.12 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.100 cfh✓
• b.40 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.On existing pressurized piping and appliance connections that cannot be depressurized for a formal test✓
• c.Only on propane tanks
• d.Never on natural gas

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.27.7 in w.c.
• b.55.4 in w.c.
• c.138.5 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.100 cfh✓
• c.65 cfh
• d.1,000 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