CSLB General Building (B) — All Questions

A house is served with natural gas having a heating value of about 1,000 Btu per cubic foot. The connected appliances are a 100,000 Btu/h furnace, a 40,000 Btu/h water heater and a 35,000 Btu/h clothes dryer. What total flow, in cubic feet per hour, must the piping downstream of the meter carry?

• a.132 cfh
• b.175 cfh✓
• c.70 cfh
• d.1,750 cfh

Add the loads: 100,000 + 40,000 + 35,000 = 175,000 Btu/h, then divide by the 1,000 Btu per cubic foot heating value to get 175 cfh. 132 cfh is what you get if the dryer is left out or a propane figure is mixed in; 70 cfh comes from dividing by 2,500, which is the propane heating value; 1,750 cfh comes from dividing by 100 instead of 1,000.IFGC §402.4

The same 175,000 Btu/h total connected load is served by LP-gas instead of natural gas. Using about 2,500 Btu per cubic foot for propane, what flow must the piping carry?

• a.70 cfh✓
• b.175 cfh
• c.437 cfh
• d.44 cfh

For propane, cfh equals Btu/h divided by 2,500, so 175,000 / 2,500 = 70 cfh. 175 cfh is the natural gas answer using 1,000 Btu/cu ft; 437 cfh comes from multiplying instead of dividing by 2.5; 44 cfh comes from using a heating value near 4,000, which no common fuel gas has.IFGC §402.4

A natural gas system runs from the meter through section A (12 ft), then section B (18 ft), then section C (35 ft) to the farthest appliance. Using the longest developed length method, which length is used to select the size of section A?

• a.12 ft, the actual length of section A
• b.30 ft, the length from the meter through section B
• c.23 ft, the average of the three sections
• d.65 ft, the total length from the meter to the farthest outlet✓

The longest length method sizes every section of the system from the single length column that corresponds to the distance from the point of supply to the most remote outlet, here 12 + 18 + 35 = 65 ft. Using 12 ft or 30 ft applies a section length rather than the developed length to the farthest outlet and undersizes the pipe; averaging section lengths is not a recognized method.IFGC §402.4

Measured along the pipe, the most remote gas outlet in a building is 78 ft from the meter. Sizing tables are printed in 10 ft length increments. Which length row should be used?

• a.70 ft, because 78 is closer to 70 than to 90
• b.75 ft, by interpolating between rows
• c.80 ft, the next length greater than the measured length✓
• d.78 ft, only if the table is redrawn to that value

When the measured developed length falls between table rows, you use the next longer row, so 78 ft is sized from the 80 ft column. Rounding down to 70 ft would allow more pressure drop than the table assumes and undersize the pipe, and neither interpolating nor inventing a 78 ft row is permitted by the sizing method.IFGC §402.4

A residential natural gas system is supplied at about 7 in w.c. from the utility meter. Which allowable pressure drop is normally used with the standard low-pressure sizing tables for this system?

• a.0.5 in w.c.✓
• b.2 psi
• c.7 in w.c.
• d.11 in w.c.

Standard low-pressure natural gas sizing at roughly 7 in w.c. supply is based on an allowable pressure drop of 0.5 in w.c., which leaves enough pressure at each appliance regulator. 2 psi is the drop used for elevated-pressure systems with line regulators; 7 in w.c. is the delivery pressure itself, not the drop; 11 in w.c. is a typical LP-gas delivery pressure.

A gas furnace sits in a basement mechanical room. Its manual shutoff valve is installed in an adjacent storage room 9 ft away, behind a closed door. Why does this installation fail inspection?

• a.Shutoff valves must be within 3 ft of the appliance
• b.The shutoff must be within 6 ft of the appliance and in the same room as the appliance✓
• c.Only the main valve at the meter is allowed to serve a furnace
• d.The valve must be downstream of the appliance regulator

Each appliance needs an accessible manual shutoff valve located in the same room as the appliance and within 6 ft of it, so a valve 9 ft away in another room is not acceptable. The 3 ft figure is a connector length limit, not a valve distance; a main valve at the meter does not satisfy the individual appliance shutoff; and the appliance shutoff belongs upstream of the appliance controls.IFGC §409.5

On which of the following appliances does the IFGC NOT require a sediment trap ahead of the appliance control valve?

• a.A 100,000 Btu/h forced-air furnace
• b.A 40 gal storage water heater
• c.A gas-fired boiler
• d.A clothes dryer✓

The IFGC exempts illuminating appliances, ranges, clothes dryers, decorative appliances, gas fireplaces and outdoor grills from the sediment trap requirement; a clothes dryer is on that list. Furnaces, water heaters and boilers all have gas control valves that must be protected, so each requires a trap located as close to the appliance inlet as practical.IFGC §408.4

A corrugated stainless steel tubing (CSST) gas system is installed in a two-story house. What is the minimum size of the copper bonding jumper used to bond the CSST system to the electrical service grounding electrode system?

• a.14 AWG
• b.12 AWG
• c.6 AWG✓
• d.10 AWG

CSST that is not listed as arc-resistant jacketed must be directly bonded with a jumper no smaller than 6 AWG copper, connected to a rigid metallic component of the gas piping upstream of the first CSST fitting. Smaller conductors such as 14, 12 or 10 AWG cannot reliably carry lightning-induced energy and would not satisfy the bonding requirement.IFGC §310

A new residential gas piping system will operate at a working pressure of 7 in w.c. (about 1/4 psi). What is the minimum test pressure required for the pressure test?

• a.0.375 psi, which is 1.5 times the working pressure
• b.3 psi✓
• c.10 psi
• d.1.5 in w.c.

The test pressure must be at least 1.5 times the proposed maximum working pressure but never less than 3 psi, and 1.5 times 1/4 psi is far below that floor, so 3 psi governs. The 0.375 psi and 1.5 in w.c. answers apply the multiplier while ignoring the 3 psi minimum; 10 psi exceeds what the code requires for this system.IFGC §406.4

The same 3 psi test is applied to the piping with a mechanical gauge. What is the minimum time the pressure must be held without any loss?

• a.10 minutes✓
• b.5 minutes
• c.30 minutes
• d.24 hours

The test duration must be at least 10 minutes, or longer if the code official or the size of the system requires it, with no drop in pressure. Five minutes is too short to satisfy the minimum, and 30 minutes and 24 hours exceed what the code requires for a standard residential test.IFGC §406.4.1

Which practice is correct when pressure testing a fuel gas piping system?

• a.Use oxygen so the test medium is dry and clean
• b.Leave appliance regulators connected so they are tested with the piping
• c.Use air, nitrogen or another inert gas and isolate appliances and regulators from the test✓
• d.Test with the fuel gas itself and check joints with an open flame

The test medium must be air, nitrogen, carbon dioxide or another inert gas, and any equipment or regulator that cannot withstand the test pressure must be disconnected or isolated with a valve. Oxygen is prohibited because it reacts violently with pipe oils, appliance regulators are damaged by test pressures well above their rating, and locating leaks with a flame is never acceptable.IFGC §406.4

A gas range is connected with a listed appliance connector that runs 4 ft from the shutoff valve to the range. Which statement about this installation is correct?

• a.It is not allowed; no connector may exceed 3 ft
• b.It is allowed only if the connector passes through the cabinet wall behind the range
• c.It is allowed only if a second connector is added to reach the valve
• d.It is allowed, because ranges and clothes dryers may use connectors up to 6 ft long✓

Most appliance connectors are limited to 3 ft, but ranges and clothes dryers are permitted connectors up to 6 ft, so a 4 ft connector is acceptable. Connectors may not pass through walls, floors, ceilings or partitions, and connectors may not be joined together or reused, which rules out the other choices.IFGC §411.1

Which material is permitted for a buried gas service line running from an outdoor meter to a detached garage, but is prohibited for the piping inside the garage?

• a.Polyethylene (PE) pipe✓
• b.Schedule 40 black steel pipe
• c.Corrugated stainless steel tubing
• d.Type L copper tube

PE pipe is permitted only outside underground and must transition to an approved metallic material before it rises above grade or enters a building, and a tracer wire or other locating means must be buried with it. Black steel, CSST and copper (where the gas is not corrosive) are all approved for aboveground interior piping, so none of them are limited to underground use.IFGC §403

A 250 gal propane tank is filled to 200 gal of usable propane. At about 91,500 Btu per gallon, roughly how many total Btu of energy are stored?

• a.1,830,000 Btu
• b.18,300,000 Btu✓
• c.183,000,000 Btu
• d.457,500 Btu

Multiply 200 gal by 91,500 Btu per gallon to get 18,300,000 Btu. The 1,830,000 and 183,000,000 answers are the same digits off by a factor of ten, and 457,500 Btu comes from using the 2,500 Btu per cubic foot vapor value instead of the per-gallon liquid value.

A propane appliance with an input of 200,000 Btu/h runs continuously. Using about 91,500 Btu per gallon, about how long will 100 gal of propane last?

• a.About 23 hours
• b.About 92 hours
• c.About 46 hours✓
• d.About 4.6 hours

100 gal holds 9,150,000 Btu, and dividing by 200,000 Btu/h gives about 45.75 hours, or roughly 46 hours. The 23 hour answer doubles the burn rate, the 92 hour answer halves it, and 4.6 hours misplaces a decimal by a factor of ten.

A kitchen is served by a branch carrying only a 65,000 Btu/h range and a 40,000 Btu/h water heater, and that branch ends 15 ft from the meter, while the farthest outlet in the house is 90 ft from the meter. What load and what length are used to size this branch?

• a.105 cfh at 90 ft✓
• b.65 cfh at 90 ft
• c.175 cfh at 15 ft
• d.105 cfh at 15 ft

The branch carries 65,000 + 40,000 = 105,000 Btu/h, which is 105 cfh of natural gas, and under the longest length method every section is sized from the 90 ft distance to the most remote outlet. Using 15 ft applies the section length instead of the developed length; 65 cfh drops the water heater; 175 cfh adds load that this branch does not actually carry.

Gas piping passes through a concrete foundation wall below grade. What does the code require at that point?

• a.The pipe must be cast solidly into the concrete with no sleeve
• b.A union must be installed inside the wall for future service
• c.The pipe may be run through the wall only if it is PE
• d.The pipe must be protected against corrosion and breakage, typically by a sleeve sealed at one end✓

Piping that penetrates a foundation or exterior wall below grade must be sleeved and protected from corrosion and from stress caused by settlement, with the annular space sealed to prevent gas or water entry. Casting pipe directly into concrete invites corrosion and shear, joints and unions may not be concealed inside the wall, and PE is not permitted to enter a building.IFGC §404

A line pressure regulator is installed on a 2 psi system serving a residence. Which requirement applies to that regulator?

• a.The shutoff valve must be installed downstream of the regulator only
• b.The regulator vent must terminate outdoors where it cannot be blocked, and a shutoff valve must be accessible upstream of the regulator✓
• c.The vent may terminate in any concealed space as long as it points down
• d.No overpressure protection is needed because the utility regulator handles it

A line regulator that requires venting must have its vent piped to the outdoors, terminated to prevent water and insect entry, and an accessible shutoff valve must be located upstream so the regulator can be isolated for service. Venting into a concealed space would discharge gas inside the building on a diaphragm failure, and downstream overpressure protection is required in addition to any utility regulator.IFGC §410