Journeyman Plumber (UPC/IPC) — 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.70 cfh
• b.175 cfh✓
• c.1,750 cfh
• d.132 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.44 cfh
• b.437 cfh
• c.175 cfh
• d.70 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.23 ft, the average of the three sections
• b.30 ft, the length from the meter through section B
• c.65 ft, the total length from the meter to the farthest outlet✓
• d.12 ft, the actual length of section A

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

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.7 in w.c.
• c.11 in w.c.
• d.2 psi

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

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

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.12 AWG
• b.10 AWG
• c.6 AWG✓
• d.14 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.10 psi
• b.3 psi✓
• c.0.375 psi, which is 1.5 times the working pressure
• 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.30 minutes
• c.24 hours
• d.5 minutes

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

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 a second connector is added to reach the valve
• c.It is allowed only if the connector passes through the cabinet wall behind the range
• 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.Schedule 40 black steel pipe
• b.Polyethylene (PE) pipe✓
• c.Type L copper tube
• d.Corrugated stainless steel tubing

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.18,300,000 Btu✓
• b.457,500 Btu
• c.183,000,000 Btu
• d.1,830,000 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 92 hours
• b.About 46 hours✓
• c.About 4.6 hours
• d.About 23 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.175 cfh at 15 ft
• b.65 cfh at 90 ft
• c.105 cfh at 15 ft
• d.105 cfh at 90 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 and directly into the poured concrete foundation wall with no sleeve of any kind
• b.The pipe must be protected against corrosion and breakage, typically by a sleeve sealed at one end✓
• c.The pipe may be run through the wall only if it is PE
• d.A union must be installed inside the wall for future service

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

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

Fuel gas piping is prohibited from being installed in or passing through which of the following?

• a.An unfinished basement used only for mechanical equipment
• b.A circulating air duct, a chimney or vent, or an elevator shaft✓
• c.An accessible attic space above the top-floor ceiling
• d.An exterior above-grade wall of a heated building

Gas piping may not run through circulating air ducts, clothes chutes, chimneys or gas vents, or elevator and dumbwaiter shafts, because a leak there would spread gas through the building or the pipe would be exposed to flue products or moving equipment. Basements, accessible attics and walls are normal, permitted routes when the piping is properly supported and protected.IFGC §404

Horizontal 3/4 inch steel gas pipe must be supported at intervals not exceeding:

• a.6 ft
• b.10 ft
• c.12 ft
• d.8 ft✓

Steel gas pipe of 3/4 inch and 1 inch is supported at not more than 8 foot intervals. The 6 foot spacing applies to 1/2 inch steel pipe, and 10 or 12 feet apply to larger-diameter piping; using too wide a spacing lets the line sag and stresses the joints.IFGC §415 (support table)

Natural gas and propane are odorized so that a leak is detectable in air at what concentration?

• a.At the lower flammable limit itself
• b.Only above the upper flammable limit
• c.At one-fifth (1/5) of the lower flammable limit✓
• d.Odorization is not required for fuel gas

Fuel gas must carry an odorant strong enough to be readily detected at one-fifth of the lower flammable (explosive) limit, giving a clear warning well before the mixture can ignite. Waiting until the LEL itself, or the upper limit, would mean the gas is already at or past ignitable concentration, and odorization is in fact required for these normally odorless gases.IFGC §401.4 / NFPA 54-58

Using a natural-gas sizing table at 0.5 in w.c. drop, a section must carry 120 cfh at a 40 ft length. The table shows 1/2 in pipe = 105 cfh and 3/4 in pipe = 220 cfh at 40 ft. What is the smallest pipe that will carry the load?

• a.3/4 inch (rated 220 cfh)✓
• b.1/2 inch (rated 105 cfh)
• c.Either size will work
• d.1 inch pipe is required

The pipe must carry at least 120 cfh, and 1/2 inch is rated for only 105 cfh, which is less than the demand, so you step up to the next size, 3/4 inch at 220 cfh. Choosing 1/2 inch undersizes the line and starves the appliance, 1 inch is larger than the 3/4 inch that already covers the load, and the two sizes are not interchangeable when one is below the demand.IFGC §402.4 (sizing tables)

A house on natural gas (about 1,000 Btu per cubic foot) has an 80,000 Btu/h furnace, a 30,000 Btu/h water heater, and a 30,000 Btu/h range. What total flow must the piping downstream of the meter carry?

• a.56 cfh
• b.14 cfh
• c.140 cfh✓
• d.1,400 cfh

Total load is 80,000 + 30,000 + 30,000 = 140,000 Btu/h, and dividing by 1,000 Btu per cubic foot gives 140 cfh. 14 and 1,400 misplace a decimal, and 56 comes from dividing by 2,500 (a propane value).

A propane appliance load totals 125,000 Btu/h. Using about 2,500 Btu per cubic foot for propane vapor, what flow must the piping carry?

• a.50 cfh✓
• b.125 cfh
• c.31 cfh
• d.500 cfh

For propane, cfh = Btu/h / 2,500, so 125,000 / 2,500 = 50 cfh. 125 cfh uses the 1,000 Btu natural-gas value, 500 cfh divides by an incorrect small value, and 31 cfh uses about 4,000 Btu per cubic foot, which no common fuel gas has.

The most remote gas outlet measures 62 ft from the meter, and the sizing table is printed in 10 ft increments. Which length row is used?

• a.70 ft✓
• b.62 ft
• c.60 ft
• d.50 ft

When the developed length falls between rows, the next longer row is used, so 62 ft is sized from the 70 ft column. Rounding down to 60 ft (or 50 ft) allows more pressure drop than the table assumes and undersizes the pipe.

At 50 ft, a natural-gas table shows 1/2 in pipe rated for 56 cfh and 3/4 in for 115 cfh. A section must carry 60 cfh. What is the smallest pipe that works?

• a.1 in
• b.1/2 in
• c.3/8 in
• d.3/4 in✓

The pipe must carry at least 60 cfh; 1/2 in is rated for only 56 cfh, which is below the demand, so you step up to 3/4 in at 115 cfh. Choosing 1/2 in starves the appliance, and 1 in is larger than needed once 3/4 in covers the load.

What is the purpose of a sediment trap (drip leg) ahead of an appliance control valve?

• a.It regulates the gas pressure
• b.It collects moisture and debris before they reach the appliance control valve✓
• c.It acts as the shutoff valve
• d.It vents the regulator

A sediment trap is a capped drip pocket that catches moisture and scale carried in the gas so they do not foul the appliance control valve (IFGC 408.4). It does not regulate pressure, shut off gas, or vent a regulator.

What is the maximum length of a listed appliance connector serving a furnace (not a range or dryer)?

• a.3 ft✓
• b.1 ft
• c.6 ft
• d.10 ft

Most appliance connectors are limited to 3 ft (IFGC 411). Ranges and clothes dryers are the exception, permitted up to 6 ft; a furnace connector is held to the 3 ft general limit.

A listed appliance connector may:

• a.Pass through a wall if it is sleeved
• b.Be joined to a second connector to gain length
• c.Be reused from a previous appliance
• d.Not pass through walls, floors, ceilings, or partitions✓

An appliance connector may not pass through any wall, floor, ceiling, or partition, may not be concealed, and may not be joined to another connector or reused (IFGC 411). Where those conditions arise, rigid pipe must be run to a valve near the appliance.

Threaded black-steel gas pipe joints are made up with:

• a.Solvent cement
• b.An approved gas-rated thread sealant (pipe dope), or PTFE tape listed for gas✓
• c.A wax ring
• d.A rubber gasket slip coupling

Steel gas-pipe threads are sealed with a joint compound or tape listed as resistant to the gas (IFGC 403.9.2). Solvent cement is for plastic, a wax ring seals a closet, and a rubber slip coupling is a drainage fitting, none rated for gas joints.

Copper tube may be used for natural gas only when:

• a.Only when painted
• b.Never permitted for natural gas under any condition, since sulfur always attacks it
• c.Only when buried underground
• d.The gas is not corrosive (limited hydrogen sulfide content)✓

Copper is permitted for fuel gas only where the gas is not corrosive to copper, meaning the hydrogen sulfide content is below the code limit (IFGC 403.4.3), because sulfur attacks copper. It is not categorically prohibited, and burial or paint is not the deciding factor.

Where is a drip leg (drip) installed in a fuel-gas piping system?

• a.Never in residential work
• b.At low points where condensate can collect, and commonly at each appliance✓
• c.Only on outdoor piping
• d.At the highest point of the system

A drip is installed at low points where liquid can collect and typically at each appliance connection so moisture is trapped before it reaches the control (IFGC 408). Placing it at the high point would defeat the purpose, and drips are used in residential systems.

Compared with air, LP-gas (propane) vapor is:

• a.Heavier than air, so it settles at low points✓
• b.Nonflammable
• c.Lighter than air, so it rises to the ceiling
• d.The same density as air

Propane vapor is heavier than air and pools in low areas such as pits, basements, and floor level, which is why LP appliances and gas detectors account for low accumulation. Natural gas, by contrast, is lighter than air and rises.

A 250-gallon propane tank is filled to the maximum safe fill of 80 percent. How many gallons of liquid propane does it hold?

• a.250 gal
• b.125 gal
• c.200 gal✓
• d.150 gal

A propane tank is filled to a maximum of 80 percent to leave room for vapor expansion, so 250 x 0.80 = 200 gal. Filling to 250 gal (100 percent) is unsafe, and 125 or 150 gal understates the 80 percent fill.

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

• a.46 hours
• b.9 hours
• c.183 hours
• d.91.5 hours✓

100 gallons holds 9,150,000 Btu, and 9,150,000 / 100,000 = 91.5 hours. Doubling the burn rate gives 46 hours, halving it gives 183 hours, and 9 hours misplaces a decimal.

What is the approximate heating value of propane vapor?

• a.About 1,000 Btu per cubic foot
• b.About 500 Btu per cubic foot
• c.About 2,500 Btu per cubic foot✓
• d.About 91,500 Btu per cubic foot

Propane vapor carries about 2,500 Btu per cubic foot, roughly two and a half times natural gas at about 1,000 Btu per cubic foot. The 91,500 figure is the energy per gallon of liquid propane, not per cubic foot of vapor.

A residence is served by a 2 psi gas system, but the appliances require about 7 in w.c. What is installed to make this work?

• a.A check valve
• b.A larger gas meter
• c.Nothing is required, because the utility service regulator already delivers the correct appliance pressure
• d.A line pressure regulator, with overpressure protection, to step the pressure down✓

An elevated-pressure (2 psi) system requires a line pressure regulator, with downstream overpressure protection, to reduce the pressure to the roughly 7 in w.c. the appliances need (IFGC 410). A larger meter or a check valve does not regulate delivery pressure.

After a gas piping system is tested and put into service, it is purged of air:

• a.Purging is not required
• b.Through an appliance burner only
• c.To the outdoors, away from ignition sources✓
• d.Into the building through a window

Piping must be purged to the outdoors or to a safe point away from any ignition source, never into an occupied space, so an air-gas mixture cannot accumulate and ignite (IFGC 406.7). Purging is required whenever a system is placed in or returned to service.

How must vertical gas piping be supported?

• a.It is never required to be supported, since the fittings alone carry the weight of the riser
• b.Every 2 ft
• c.At each floor level, and at intervals that prevent movement✓
• d.Only at the top of the riser

Vertical gas piping must be supported at each floor level (and at intervals for larger pipe) so its weight is carried and it cannot shift and stress the joints (IFGC 415). Supporting only the top, or not at all, leaves the riser unsupported.

A gas meter must be located:

• a.In a ventilated, accessible location clear of ignition sources and building openings✓
• b.Inside a sealed closet
• c.Inside a return-air plenum
• d.Below grade inside a covered pit in every case, so that the meter is protected from the weather

A gas meter is placed in a ventilated, accessible location where a leak can disperse and away from ignition sources, windows, and air intakes. A sealed closet or a return-air plenum would trap or distribute leaking gas.

What is the minimum depth of cover for underground gas piping in an area with no vehicle traffic?

• a.36 in
• b.24 in
• c.6 in
• d.12 in✓

Underground gas piping requires at least 12 in of cover in general (IFGC 404.12). 6 in leaves the pipe vulnerable to damage, and 24 or 36 in is deeper than the general minimum (deeper cover applies under driveways and roads).

What is the minimum depth of cover for underground gas piping installed beneath a private driveway?

• a.6 in
• b.36 in
• c.12 in
• d.18 in✓

Under a driveway or parking area the cover is increased to at least 18 in to protect the pipe from vehicle loads (IFGC 404.12). The 12 in general minimum is not enough under traffic, and 6 in is far too shallow.

Which of the following is prohibited in a concealed gas-piping location?

• a.A straight, unbroken length of pipe with no fittings at all
• b.A union, bushing, or right-and-left coupling✓
• c.A welded joint
• d.An elbow

Unions, bushings, swing joints, and right-and-left couplings are prohibited in concealed locations because they are the joints most likely to loosen and leak where no one can inspect them (IFGC 404.5). Welded joints and standard fittings on run pipe are permitted concealed.

On detecting a gas leak in a building, which action must you NOT take?

• a.Operating electrical switches or creating any spark or flame✓
• b.Shutting the gas off at the meter if it is safe to do so
• c.Leaving the area
• d.Calling the utility from outside the building

You must not operate electrical switches, light a flame, or do anything that could create a spark, since any of these can ignite an accumulated gas-air mixture. The correct steps are to evacuate, shut off the gas if safe, and call the utility from a safe location outside.