Journeyman Plumber (UPC/IPC) — All Questions

Static pressure at the main is 72 psi. Meter loss at design flow is 9 psi, the highest fixture is 26 ft above the meter, and 15 psi residual is required at that fixture. How much pressure is available to overcome friction loss in the piping?

• a.About 41.2 psi
• b.About 25.5 psi
• c.About 48.0 psi
• d.About 36.7 psi✓

Elevation loss is 26 x 0.433 = 11.26 psi, so 72 - 9 - 11.26 - 15 = 36.7 psi available for friction. The 48.0 psi answer forgets the required residual pressure, and 41.2 psi forgets part of the elevation loss. The 25.5 psi answer subtracts the residual twice or uses a 20 psi flushometer residual that this problem did not specify.UPC §610.0

A flushometer water closet on the top floor requires 20 psi residual. Static pressure is 65 psi, combined meter and backflow preventer loss is 10 psi, and the flush valve is 34 ft above the meter. How much pressure remains for friction loss in the piping and fittings?

• a.About 35.0 psi
• b.About 14.7 psi
• c.About 25.3 psi
• d.About 20.3 psi✓

Elevation loss is 34 x 0.433 = 14.72 psi, so 65 - 10 - 14.72 - 20 = 20.3 psi for friction. The 35.0 psi answer ignores the elevation loss, and 25.3 psi uses a 15 psi residual instead of the 20 psi a flushometer needs. The 14.7 psi choice is the elevation loss itself, not the friction allowance.UPC §610.0

A sizing problem leaves 24 psi available for friction loss. The measured developed length to the most remote fixture is 160 ft, and fittings are estimated to add 50 percent to that length. What is the allowable friction loss per 100 ft of pipe?

• a.About 6.7 psi per 100 ft
• b.About 10 psi per 100 ft✓
• c.About 24 psi per 100 ft
• d.About 15 psi per 100 ft

Total equivalent length is 160 x 1.5 = 240 ft, so 24 psi / 240 ft x 100 = 10 psi per 100 ft. The 15 psi answer divides by the measured 160 ft and skips the fitting allowance. The 6.7 psi answer overstates the equivalent length, and 24 psi per 100 ft simply restates the total budget without dividing by length.UPC §610.0

A dwelling unit contains one flush tank water closet (2.5 WSFU), two lavatories (1.0 WSFU each), one bathtub with shower (4.0 WSFU), one kitchen sink (1.5 WSFU), one dishwasher (1.5 WSFU), and one clothes washer (4.0 WSFU). What is the total water supply fixture unit load?

• a.16.5 WSFU
• b.15.5 WSFU✓
• c.14.5 WSFU
• d.13.0 WSFU

Adding the listed values gives 2.5 + 1.0 + 1.0 + 4.0 + 1.5 + 1.5 + 4.0 = 15.5 WSFU. The 14.5 answer counts only one lavatory, and 13.0 drops the dishwasher. The 16.5 answer adds an extra fixture unit that is not in the list; the total load is then carried into the sizing table to pick the service and distribution sizes.

Using the standard fixture unit to gpm conversion curve, what happens to the estimated demand when the total water supply fixture unit load on a system is doubled?

• a.The demand in gpm increases by less than double✓
• b.The demand in gpm more than doubles
• c.The demand in gpm exactly doubles
• d.The demand in gpm stays the same

The conversion curve is probability based: as more fixtures are added, the chance that all of them run at once drops, so gpm rises more slowly than fixture units. This diversity is why a 200 WSFU building does not need twice the flow of a 100 WSFU building. Assuming a straight-line doubling oversizes the service, and the more-than-double and no-change answers contradict how the curve behaves.IPC Appendix E

What is the minimum nominal size normally permitted for a water service pipe serving a building?

• a.5/8 in
• b.3/4 in✓
• c.1 in
• d.1/2 in

The water service pipe may not be smaller than 3/4 in regardless of what the fixture unit calculation produces. A 1/2 in service is below the code floor even for a very small single-fixture building, and 5/8 in is a meter size designation, not a standard pipe size. Requiring 1 in as the minimum is stricter than the code and would be a design choice, not a code requirement.

The highest fixture in a building is 28 ft above the meter and requires 15 psi residual. Meter loss is 5 psi and calculated friction loss in the piping is 12 psi. What minimum static pressure is needed at the meter?

• a.About 55.1 psi
• b.About 44.1 psi✓
• c.About 32.0 psi
• d.About 40.0 psi

Add every loss to the required residual: 28 x 0.433 = 12.12 psi elevation, plus 5 psi meter, plus 12 psi friction, plus 15 psi residual equals 44.1 psi. The 32.0 psi answer omits the elevation loss, and 40.0 psi rounds the elevation loss down to about 8 psi. The 55.1 psi answer double counts one of the losses and would call for a booster that is not actually needed.UPC §610.0

Using velocity (fps) = 0.408 x flow (gpm) divided by the square of the inside diameter (in), what is the velocity of 12 gpm flowing in 3/4 in Type L copper with an inside diameter of 0.785 in?

• a.About 10.2 fps
• b.About 6.0 fps
• c.About 4.4 fps
• d.About 7.9 fps✓

0.408 x 12 = 4.896, and 0.785 squared is 0.616, so 4.896 / 0.616 = 7.9 fps, right at the practical 8 fps cold water limit. The 4.4 and 6.0 answers come from dividing by the diameter instead of the diameter squared or from using the nominal 3/4 in size. The 10.2 answer uses a smaller inside diameter such as 0.69 in, which belongs to a heavier wall tube.

A 60 ft straight run of CPVC hot water pipe will see a 70 degree F temperature change. Using a coefficient of thermal expansion of 0.000034 in per in per degree F, approximately how much will the run expand?

• a.About 2.4 in
• b.About 1.7 in✓
• c.About 1.0 in
• d.About 0.6 in

Convert to inches first: 60 ft = 720 in, and 720 x 0.000034 x 70 = 1.71 in of movement, which is why an offset or expansion loop is needed. The 0.6 in and 1.0 in answers come from using only part of the temperature change or forgetting the foot-to-inch conversion. The 2.4 in answer uses a temperature change near 100 degrees F rather than the 70 degrees stated.

An existing galvanized steel water line is being extended with copper tube. What must be installed at the point where the two materials join?

• a.An approved dielectric fitting or dielectric union✓
• b.A rubber sleeve coupling with stainless steel clamps
• c.A soldered joint made directly to the steel pipe
• d.A brass compression coupling

Copper and galvanized steel are far apart on the galvanic scale, so a dielectric fitting is required to break the metallic path and prevent accelerated corrosion at the joint. A brass coupling still conducts and only shifts the corrosion cell rather than stopping it. Copper cannot be soldered directly to galvanized steel, and a rubber sleeve coupling is a drainage fitting that is not rated for water distribution pressure.IPC §605

A water closet is being roughed in against a side partition in a narrow alcove. Measuring from the finished face of the partition to the center of the closet outlet, what is the minimum dimension the model plumbing codes require?

• a.12 inches
• b.14 inches
• c.18 inches
• d.15 inches✓

The centerline of a water closet must be at least 15 inches from any side wall, partition, or vanity, which is what makes a 30 inch wide alcove the practical minimum for a single fixture. The 12 inch figure is the standard rough-in distance from the finished back wall to the closet flange center, not a side clearance. 14 inches and 18 inches are not code minimums; 18 inches is a common designer's comfort dimension and 14 inches is simply short of the requirement.IPC §405.3.1

Two water closets are to be installed side by side in a school restroom. What is the minimum distance between the centerline of one closet and the centerline of the adjacent closet?

• a.36 inches
• b.24 inches
• c.21 inches
• d.30 inches✓

Because each closet needs 15 inches of clearance on each side of its centerline, two adjacent closets require 15 plus 15, or 30 inches center to center. The 24 inch and 21 inches figures are front clearance numbers, not lateral spacing. 36 inches exceeds the requirement and would be an accessibility compartment width rather than the general fixture spacing minimum.

A framed water closet compartment measures 32 inches wide inside the finished surfaces, and the closet is set exactly on the center of that width. Does the installation satisfy the side clearance requirement?

• a.No, the centerline is only 15 inches from each side and 16 inches is required
• b.Yes, the centerline is 16 inches from each side, which exceeds the 15 inch minimum✓
• c.Yes, but only because a compartment is exempt from side clearance rules
• d.No, a compartment must be at least 36 inches wide in all cases

Half of 32 inches is 16 inches, so each side has 16 inches of clearance from the centerline, one inch more than the 15 inch minimum. The requirement is 15 inches, not 16, so the first choice reverses the numbers. Compartments are not exempt from clearance rules, and 36 inches is an accessible-stall dimension rather than a universal minimum.

Under the International Plumbing Code, what is the minimum clear space required in front of a water closet, measured from the front edge of the fixture to any wall or obstruction?

• a.24 inches
• b.15 inches
• c.21 inches✓
• d.30 inches

The IPC requires 21 inches of clear space in front of a water closet, lavatory, or bidet, although some jurisdictions and the UPC require 24 inches. 15 inches is the side clearance from the centerline, not a front dimension. 30 inches is the center-to-center spacing between two closets and has nothing to do with front approach space.IPC §405.3.1

A building owner replaces 40 old 3.5 gpf water closets with 1.28 gpf high efficiency models. If the fixtures are flushed a combined total of 2,000 times per day, how much water is saved per day?

• a.5,120 gallons
• b.3,500 gallons
• c.4,440 gallons✓
• d.2,560 gallons

The savings per flush is 3.5 minus 1.28, or 2.22 gallons, and 2.22 times 2,000 flushes equals 4,440 gallons per day. 2,560 gallons is 1.28 times 2,000, the new consumption rather than the savings. 5,120 and 3,500 gallons come from doubling the new usage or from using the old flush volume alone, neither of which is a difference calculation.IPC §604.4

A storage type water heater is being installed. Which device must be provided on the tank to protect against both excessive temperature and excessive pressure?

• a.A backflow preventer on the cold water inlet
• b.A vacuum relief valve at the top of the tank
• c.A pressure reducing valve on the building supply
• d.A combination temperature and pressure relief valve✓

Every storage water heater must be equipped with an approved combination temperature and pressure relief valve, typically rated to open at 210 degrees F and 150 psi. A vacuum relief valve prevents siphoning of the tank on bottom-fed heaters but does not relieve pressure or temperature. A backflow preventer and a pressure reducing valve address contamination and supply pressure, not tank overpressure or overheating.IPC §504.4

A temperature and pressure relief valve has a 3/4 inch outlet. Which discharge piping arrangement is acceptable?

• a.3/4 inch pipe running by gravity to terminate 8 inches above the floor with a plain end✓
• b.1/2 inch copper reduced at the valve and terminating 30 inches above the floor
• c.3/4 inch pipe with a threaded cap installed on the terminal end
• d.3/4 inch pipe with a ball valve installed for service isolation

Discharge piping must be full size of the valve outlet with no reduction, must drain by gravity, must have no valve in the line, and must terminate between 6 and 24 inches above the ground or an approved receptor with no threads on the end. The 1/2 inch option reduces the pipe and terminates too high, the ball valve option installs a prohibited shutoff, and the threaded cap option both threads the end and blocks discharge entirely.IPC §504.6

A 50 gallon water heater is installed in the attic above a finished ceiling. A drain pan is required. What is the minimum size of the pan drain line?

• a.3/4 inch✓
• b.1 inch
• c.5/8 inch
• d.1/2 inch

Where leakage would cause damage to the structure, a pan is required and its indirect drain must be at least 3/4 inch in diameter, discharging to an approved location. 1/2 inch and 5/8 inch are undersized and would not carry the flow of a leaking tank. A 1 inch pan drain is permitted as an upsize but is not the code minimum being asked for.IPC §504.7

A gas fired water heater is installed in a residential garage in a seismic zone. It must be strapped in two places. Where must the lower strap be located relative to the heater's controls?

• a.At least 4 inches above the controls✓
• b.At least 4 inches below the controls
• c.At the exact vertical midpoint of the tank
• d.Directly across the control housing

The two straps go around the upper third and the lower third of the tank, and the lower strap must be at least 4 inches above the controls so the strap does not damage or obstruct the gas valve and thermostat. Strapping across or below the controls interferes with service and with the control housing itself. A single midpoint strap does not satisfy the two-point bracing requirement.

The same gas water heater is installed in that garage on a concrete slab. What is the minimum height that the source of ignition must be elevated above the garage floor?

• a.18 inches✓
• b.24 inches
• c.12 inches
• d.6 inches

Ignition sources in a garage must be at least 18 inches above the floor because gasoline vapors are heavier than air and pool at floor level. 12 inches and 6 inches leave the burner inside the vapor layer. 24 inches is higher than required and is not the code figure, although a taller platform would still comply.

A 120,000 Btu/h gas water heater draws all of its combustion air directly from outdoors through two vertical ducts. Using the 1 square inch per 4,000 Btu/h rule for vertical ducts, what is the required free area of each opening?

• a.15 square inches
• b.12 square inches
• c.30 square inches✓
• d.60 square inches

Dividing 120,000 by 4,000 gives 30 square inches, and that is the required free area for each of the two openings, one near the top and one near the bottom of the enclosure. 60 square inches is the combined area of both openings, not the size of each. 15 square inches halves the correct figure, and 12 square inches corresponds to no recognized ratio.

A 100,000 Btu/h water heater is placed in a closet and will take combustion air from inside the building only. Using the rule of thumb of 50 cubic feet of room volume per 1,000 Btu/h, what minimum volume of communicating space is needed?

• a.10,000 cubic feet
• b.3,000 cubic feet
• c.5,000 cubic feet✓
• d.2,000 cubic feet

Dividing 100,000 by 1,000 gives 100, and 100 times 50 cubic feet equals 5,000 cubic feet of communicating volume. 2,000 and 3,000 cubic feet come from applying a 20 or 30 cubic foot factor that the standard indoor air method does not use. 10,000 cubic feet doubles the requirement and would only be relevant if two such appliances shared the space.

Where an enclosure takes combustion air from an adjacent room through two permanent openings, where must those openings be located?

• a.One opening at the ceiling and one located at any convenient height on an outside wall of the room
• b.Both within 12 inches of the ceiling of the enclosure
• c.One within 12 inches of the top of the enclosure and one within 12 inches of the bottom✓
• d.Both within 12 inches of the floor of the enclosure

The two-opening method requires one opening within 12 inches of the top and one within 12 inches of the bottom of the enclosure so that heated air can exhaust high while replacement air enters low. Placing both openings high or both low defeats the convective loop that drives the air exchange. Locating the lower opening at any convenient height does not satisfy the 12 inch dimension.

A shower compartment is framed 32 inches by 32 inches inside the finished walls. Does it meet the minimum area and minimum dimension requirements for a shower?

• a.No, the minimum interior dimension is 36 inches in every direction
• b.Yes, 1,024 square inches meets the area minimum and 32 inches exceeds the 30 inch dimension minimum✓
• c.No, the area works out to 1,024 square inches but a minimum of 1,200 square inches is required for a stall
• d.Yes, but only if a 30 inch wide door is installed

32 times 32 equals 1,024 square inches and each interior dimension of 32 inches clears the 30 inch minimum, so the stall complies. Code divergence: the UPC (§411.7) sets the minimum area at 1,024 square inches, which 32 by 32 meets exactly, while the IPC (§417.4) sets it lower at 900 square inches, so 1,024 clears both codes. The 1,200 square inch figure and a universal 36 inch interior dimension are not code minimums, and a shower door need only provide a 22 inch clear opening, so a 30 inch door is not what makes the stall compliant.UPC §411.7 / IPC §417.4

An indirect waste pipe from a commercial ice machine is 1-1/2 inches in diameter and discharges into a floor sink. What is the minimum required air gap?

• a.2 inches
• b.1 inch
• c.1-1/2 inches
• d.3 inches✓

The air gap for an indirect waste must be at least twice the effective diameter of the discharge pipe, so 2 times 1-1/2 inches equals 3 inches measured from the pipe outlet to the flood level rim of the receptor. 1 inch is only the absolute minimum air gap for very small pipes. 2 inches and 1-1/2 inches apply the wrong multiplier to the pipe size.IPC §802.2

A 3/8 inch indirect waste tube from a beverage dispenser discharges over an open receptor. Applying the air gap rule, what is the required air gap?

• a.3/8 inch
• b.3/4 inch
• c.1-1/2 inches
• d.1 inch✓

Twice the pipe diameter would be only 3/4 inch, but the code also sets an absolute floor of 1 inch, so the required air gap is 1 inch. The 3/4 inch answer applies the multiplier and ignores the minimum. 1-1/2 inches and 3/8 inch are not produced by either part of the rule.IPC §802.2

A laundry standpipe for a residential clothes washer is roughed in with the top of the standpipe 14 inches above the trap weir. Is the installation acceptable?

• a.Yes, any height is acceptable as long as the trap is vented
• b.No, the standpipe must be at least 24 inches and not more than 60 inches above the trap weir
• c.Yes, 14 inches is within the allowable range
• d.No, the standpipe must extend at least 18 inches and not more than 42 inches above the trap weir✓

A clothes-washer standpipe must be a minimum of 18 inches above the trap weir, so 14 inches is too short and the discharge is likely to back out of the pipe. Height is regulated regardless of venting, so the first choice is wrong. Code divergence is on the maximum: the IPC (§802.4) allows up to 42 inches while the UPC (§807.4) caps it at 30 inches; the 18 inch minimum is common to both codes, which is why 14 inches fails under either code. The 24 to 60 inch range in the second choice is not a code window under either code.IPC §802.4 / UPC §807.4

A showerhead is rated at the maximum allowable flow. A user showers for 8 minutes. Assuming the head flows at its rated maximum, how much water is used?

• a.12.0 gallons
• b.24.0 gallons
• c.17.6 gallons
• d.20.0 gallons✓

The maximum showerhead flow rate is 2.5 gpm at 80 psi, and 2.5 times 8 minutes equals 20 gallons. 17.6 gallons would result from a 2.2 gpm lavatory faucet rate, which does not apply to showerheads. 12 gallons uses a 1.5 gpm rate and 24 gallons uses 3.0 gpm, neither of which is the code maximum for a shower.IPC §604.4

A public restroom is fitted with metering faucets. What is the maximum volume of water each faucet may deliver per metering cycle?

• a.0.25 gallon✓
• b.1.0 gallon
• c.0.5 gallon
• d.0.125 gallon

Public metering faucets are limited to 0.25 gallon per metering cycle, which is a volume limit rather than a flow rate limit because the valve shuts itself off. 0.5 gallon and 1.0 gallon are urinal flush volumes, not faucet cycle volumes. 0.125 gallon is half the allowance and is not a code figure.

A closet flange is set on a wood subfloor before the finished tile is installed, and the installer plans to seal the closet to the flange. Which practice is correct?

• a.Seal the flange to the bowl with structural construction adhesive instead of using any mechanical fasteners at all, then set the bowl
• b.Rely on the closet bolts alone to hold the flange to the floor
• c.Set the flange on top of the finished floor, secure it to the structure with fasteners, and seal with a wax or approved gasket✓
• d.Set the flange below the finished floor and shim the bowl with wood blocks

The closet flange must rest on and be mechanically secured to the finished floor or structure, and the joint between the bowl horn and the flange is sealed with a wax ring or an approved elastomeric gasket. A flange set below the finished floor leaves a gap that the seal cannot reliably bridge, and shimming with wood blocks is not an approved support method. Adhesive does not replace fasteners, and closet bolts secure the fixture to the flange rather than the flange to the floor.

A restaurant installs a grease interceptor sized for 30 minutes of retention. If the connected fixtures produce a peak flow of 25 gallons per minute through the flow control device, what liquid capacity does the retention rule call for?

• a.250 gallons
• b.750 gallons✓
• c.1,500 gallons
• d.500 gallons

Retention volume equals flow rate times retention time, so 25 gpm times 30 minutes equals 750 gallons. 250 gallons corresponds to only 10 minutes of retention and 500 gallons to 20 minutes, both short of the design basis stated in the question. 1,500 gallons would represent a full hour of retention, twice what was specified.

A grease interceptor is inspected and found to contain accumulated grease and settled solids filling 25 percent of the total liquid depth. What action does the common maintenance standard require?

• a.Install a larger flow control device on the inlet to slow the incoming wash-water flow rate
• b.Pump and clean the interceptor, since the 25 percent threshold has been reached✓
• c.No action; cleaning is required only at 50 percent
• d.Add an enzyme treatment and re-inspect in six months

The widely used 25 percent rule requires that an interceptor be pumped when grease and solids occupy a quarter of the liquid depth, because beyond that point retention efficiency falls off sharply. Waiting for 50 percent allows grease carryover into the building drain. Enzyme or chemical treatments emulsify grease so it passes through the unit rather than being retained, and changing the flow control does not remove the accumulated material.IPC §1003.3

A residence has a pressure reducing valve with a check on the incoming water service, and the 40 gallon water heater's relief valve has begun weeping each evening. What is the most likely cause and the correct correction?

• a.The heater is oversized; reduce the thermostat to 90 degrees F
• b.The discharge line is too long; shorten it and add a threaded cap
• c.The relief valve is set too high; replace it with a 250 degree F valve
• d.Thermal expansion in a closed system; install an expansion tank sized for the system✓

A check or pressure reducing valve makes the system closed, so water expanding as it heats has nowhere to go and pressure rises until the relief valve lifts, which is corrected with a properly sized thermal expansion tank. Replacing the relief valve with a higher setting defeats the safety device rather than solving the pressure problem. Lowering the thermostat to 90 degrees F creates a bacterial growth risk, and capping the discharge line is expressly prohibited.

A three compartment pot sink and a food prep sink are being connected in a commercial kitchen. How must the waste from food handling equipment such as a food prep sink be connected to the drainage system?

• a.Directly connected but only through a grease interceptor
• b.Directly connected through a P-trap with no air gap or air break
• c.Indirectly connected through an air gap to an approved receptor✓
• d.Indirectly connected through an air break, which is acceptable for all food equipment

Waste from equipment in which food is stored, prepared, or handled must be indirectly connected by means of an air gap so that sewage cannot back up into food contact surfaces. A direct connection provides no physical break at all, even when a trap or interceptor is present. An air break relies on the pipe extending below the flood rim and is permitted for some indirect wastes but not for food handling equipment.IPC §802.1

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.