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Fuel Gas Piping — Plumber Practice Questions

53 questions · 8% of the Plumber exam

Worked questions

1. Under unamended 2021 IFGC Section 408.4, which of these gas appliances requires a sediment trap in its supply when no trap is incorporated into the appliance?

  • AA domestic clothes dryer
  • BA residential gas range
  • A storage-type gas water heater
  • DAn outdoor gas grill

Where to look it up

https://www.ncosfm.gov/b-2-2024-ncfgc/open

Why C is correct

A storage water heater is not among the listed exceptions, whereas the range, clothes dryer and outdoor grill are. For an appliance requiring a separate trap, install it downstream of the appliance shutoff valve as close to the inlet as practical. The specified tee arrangement has a capped nipple installed vertically in its bottommost opening, or another approved effective device may be used. Do not expand the named exceptions into every outdoor or decorative gas appliance. See PDF p.87; NC-added exception wording and MP-regulator provision are not relied on. Source: 2021 IFGC model text reproduced in OSFM comparison, https://www.ncosfm.gov/b-2-2024-ncfgc/open

2. A unit heater needs an ordinary threaded union that is not a listed CSST fitting. Under unamended 2021 IFGC Section 404.5 and the definition of concealed location, which proposed location avoids the concealed-fitting restriction?

  • AInside a sealed wall chase that can be reached only by cutting permanent drywall
  • BAbove a fixed plaster ceiling that must be broken for access
  • CInside a closed floor assembly requiring removal of permanent finish for access
  • In exposed, accessible piping beside the heater on the appliance side of its shutoff valve

Where to look it up

https://www.ncosfm.gov/b-2-2024-ncfgc/open

Why D is correct

Section 404.5 limits fitting types in concealed locations; an ordinary threaded union is not in that list. The definition concerns whether access requires damage to permanent structure or finish. Spaces behind readily removable panels or doors are not concealed merely because they are out of sight. Thus a removable suspended ceiling or an accessible crawl space cannot automatically be rejected as concealed, as the original explanation did. The exposed appliance location avoids the stated restriction; other appliance, valve, listing and installation requirements still apply. See PDF pp.14 and 83. Source: 2021 IFGC model text reproduced in OSFM comparison, https://www.ncosfm.gov/b-2-2024-ncfgc/open

3. A project’s approved fuel-gas route runs on the exterior wall, with specified supports and corrosion and impact protection. A proposed change omits that protection without approval. What is the appropriate response?

  • AAssume exterior piping never needs protection.
  • BAccept the change because support spacing alone covers every requirement.
  • Resolve the deviation and provide the specified protection before accepting the installation.
  • DReject all return-air-plenum routes categorically without checking the applicable provisions.

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why C is correct

The stated approved route includes protective conditions that the change omits. Evaluate those actual requirements; the original blanket equation of a plenum with every prohibited duct was unsupported.

4. A propane system serves a 90,000 BTU per hour furnace, a 40,000 BTU per hour water heater and a 65,000 BTU per hour range. Using a heating value of 2,500 BTU per cubic foot for propane, what is the total demand of the system in cubic feet per hour?

  • A52 cubic feet per hour

    52 cubic feet per hour is what you get by leaving the range out of the total, dividing 130,000 by 2,500. Every connected appliance counts toward system demand.

  • B62 cubic feet per hour

    62 cubic feet per hour comes from omitting the water heater, dividing 155,000 by 2,500. Dropping an appliance from the tally is the most common arithmetic slip in gas sizing.

  • 78 cubic feet per hour
  • D195 cubic feet per hour

    195 cubic feet per hour is the natural gas answer, using roughly 1,000 BTU per cubic foot. Applying the natural gas heating value to a propane system inflates the volume by about two and a half times.

Why C is correct

The total connected load is 195,000 BTU per hour, and dividing that by the fuel's heating value of 2,500 BTU per cubic foot converts it to 78 cubic feet per hour. Volume demand is always energy demand divided by heating value, so the fuel type decides the divisor.

What this question is testing

This tests whether you can total connected loads correctly and whether you know that the BTU-to-volume conversion depends on the fuel, not on the pipe.

On the job

Tank and regulator sizing runs on cubic feet per hour, but every appliance nameplate is in BTU per hour, so the conversion happens on every propane job. The reverse error is just as common: quoting a propane system's demand to a natural gas utility. Remember that the maximum demand of a system is the sum of the connected appliance inputs, without a diversity factor, unless the code or the utility explicitly allows one for a specific occupancy.

Memory technique

Add every nameplate, then divide by the fuel's heat per cubic foot.

Exam tip

Natural gas is about 1,000 BTU per cubic foot, propane about 2,500. Check which fuel the question names before you divide.

Where to look it up

Maximum gas demand is IFGC Chapter 4, Section 402.2, and the sizing tables that follow are split by fuel. UPC jurisdictions use UPC Chapter 12 or NFPA 54 tables, which are organized differently.

5. A new gas piping system is to be pressure tested at 10 psig. Take as given the rule that the test gauge must be selected so that the test pressure falls between 20 percent and 80 percent of the gauge's full scale range. Which gauge satisfies that rule?

  • A 30 psi gauge
  • BA 10 psi gauge, matching the test pressure exactly
  • CA 100 psi gauge, giving plenty of margin above the test pressure
  • DA 200 psi gauge, so that the needle can never be driven off the scale

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why A is correct

Apply the supplied 20–80 percent rule. At 10 psi, a 30 psi full-scale gauge reads 10 / 30 = 33.3 percent of full scale and passes. The other choices read 100 percent, 10 percent and 5 percent, respectively, so each fails a stated boundary. Equivalently, acceptable full-scale values run from 10 / 0.80 = 12.5 psi through 10 / 0.20 = 50 psi. This checks only the given range rule; resolution, accuracy, calibration and applicable test requirements must also be checked.

6. A gas piping section must carry 220 cubic feet per hour at a design length of 100 feet. Use these supplied capacities: at 7 inches water column with a 0.5-inch water-column drop, 1-inch pipe carries 175 cubic feet per hour and 1-1/4-inch pipe carries 360; at a delivery pressure of 1/2 psi with a 1.0-inch water-column drop, 3/4-inch pipe carries 240 cubic feet per hour and 1-inch pipe carries 450. After conversion to the stated 1/2 psi system with line regulators ahead of the appliances, what is the smallest pipe size demonstrated to meet the demand by the supplied capacities?

  • A1-1/4 inch, because the 7 inch water column table still governs and 1-inch pipe carries only 175 there
  • B1 inch, because a section carrying 220 cubic feet per hour may never be smaller regardless of pressure
  • C1/2 inch, because raising the delivery pressure doubles the capacity of every size in the table
  • 3/4 inch, because at the 1/2 pound delivery pressure that size is rated for 240 cubic feet per hour

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why D is correct

Use the supplied capacities for the converted system. A 3/4-inch pipe carries 240 cubic feet per hour, exceeding the required 220 by 20. The supplied 1-inch capacity also passes but uses a larger pipe. No capacity is supplied for 1/2-inch pipe, so these data cannot justify selecting it. The 7-inch-water-column values describe different conditions. This is a comparison of the given data, not an independently verified sizing table; actual design also requires the correct material, gas, pressure, length and regulator requirements.

47 more in the bank

Answers and explanations for these are in the app.

  • Which piping material is acceptable for the interior fuel gas piping of a natural gas system in a commercial building?
  • What is the function of an automatic excess flow valve installed in a fuel gas piping system?
  • How must a corrugated stainless steel tubing gas piping system be electrically bonded in a building?
  • Where must a sediment trap be located relative to the appliance shutoff valve and the appliance it serves?
  • Where must the shutoff valve serving an individual gas appliance be located under the fuel gas code?
  • When a natural gas piping system is sized by the longest length method, which length is used to enter the sizing table for every section of the system?
  • A natural gas system runs 20 feet from the meter to a tee. From that tee one branch runs 15 feet to a 100,000 BTU per hour furnace and the other branch runs 60 feet to a 40,000 BTU per hour water heater. In the table given for this system, the 40-foot column allows 1/2-inch pipe to carry 68,000 BTU per hour, 3/4-inch to carry 143,000 and 1-inch to carry 268,000; the 80-foot column allows 1/2-inch to carry 45,000, 3/4-inch to carry 95,000, 1-inch to carry 180,000 and 1-1/4-inch to carry 370,000. What size is required for the 20-foot section between the meter and the tee?
  • An 80,000 BTU per hour furnace and a 40,000 BTU per hour water heater draw combustion air from the room they are installed in. Using the standard indoor air method, which requires 50 cubic feet of room volume for every 1,000 BTU per hour of combined appliance input, what minimum room volume is required?
  • A new gas piping system will operate at a maximum working pressure of 1 psig. The code requires the test pressure to be at least one and one-half times the proposed maximum working pressure, and in no case less than three pounds per square inch gauge. What is the minimum acceptable test pressure?
  • The piping in a new gas system contains 1,100 cubic feet of volume. The code sets the test duration at not less than one-half hour for each 500 cubic feet of pipe volume or any fraction of that amount. What is the minimum length of the pressure test?
  • You are purging air out of a newly installed gas branch inside an occupied building. Which practice meets the intent of the fuel gas code?
  • A Type B gas vent passes through a roof. Beyond the minimum height above the roof surface itself, which clearance governs where the vent terminates?
  • An isometric is being sized using the branch length method. Which distance governs the sections of a branch that does not lie along the longest run in the system?
  • Gas capacity tables are published as a set, and picking the wrong one gives a wrong answer no matter how carefully you measure. Besides the type of gas and the piping material, what two system conditions determine which table you enter?
  • Corrugated stainless steel tubing is being routed through bored holes in studs and joists on a residential job. What does the fuel gas code require where that tubing passes through or close to a framing member?
  • A line pressure regulator installed inside a building is vented rather than fitted with a listed vent limiting device. What does the fuel gas code require of the vent outlet?
  • A gas furnace is installed in an attic that is reached through an access opening in a hallway ceiling. Where does the fuel gas code allow the appliance shutoff valve to be located?
  • A gas line has to cross a building where a return air duct, an elevator shaft and an abandoned clothes chute all offer convenient paths. Which routing does the fuel gas code accept?
  • A seismic gas shutoff valve is installed on the line serving a building. What does that valve do, and what has to happen after it operates?
  • You have finished purging air from a newly installed gas branch and are about to put the appliances back in service. How does the fuel gas code expect the piping and connections to be checked for leakage?
  • A house is served by a 100,000 BTU per hour furnace, a 40,000 BTU per hour water heater, a 65,000 BTU per hour range and a 30,000 BTU per hour clothes dryer. The owner points out that all four never run at the same moment. What demand is carried into the sizing table for the piping leaving the point of delivery?
  • A two pound gas system runs 80 feet from the meter to a line regulator, then 25 feet from that regulator to the appliances, which total 160 cubic feet per hour. Take these capacities as given: at 2 psi with the pressure drop used for that portion, 1/2-inch pipe carries 350 cubic feet per hour at 80 feet. At 7 inches water column with a half inch drop at 25 feet, 1/2-inch pipe carries 45, 3/4-inch carries 95 and 1-inch carries 175 cubic feet per hour. What sizes are required?
  • A mechanical closet takes combustion air from an adjacent interior space through two permanent openings. Where does the fuel gas code require those openings to be located?
  • A combustion air opening must provide 100 square inches of free area. It will be covered with a wood louver, and take as given the customary assumption that a wood louver provides 25 percent free area unless the manufacturer states otherwise. What gross opening must be framed?
  • Gas pipe sizing lengths and much of the code's scope are measured from the point of delivery. For a building supplied by a utility through a meter set with a service regulator, where is the point of delivery?
  • A steel gas line runs from an outdoor meter into a building through a poured concrete foundation wall. How must that penetration be made?
  • A steel gas line will be installed underground from the meter to a detached building. What does the fuel gas code require for that buried steel piping?
  • A building is served at 2 pounds per square inch of gas pressure, while the appliances inside are rated for a supply of a few inches of water column. What does the fuel gas code require between the two?
  • New gas piping is about to be pressure tested at a pressure well above the system's operating pressure, and the appliances, the meter and a line regulator are already connected. What does the fuel gas code require before the test?
  • A commercial building is served by a single gas meter set outside. Under the fuel gas code, what shutoff arrangement must serve the piping system in that building?
  • Threaded steel gas piping is being assembled for a propane system. What does the fuel gas code require of the joint compound or tape used on those threads?
  • A corrugated stainless steel tubing run 55 feet long must carry 120,000 BTU per hour of natural gas. Take these capacities at 55 feet as given data: EHD 15 carries 39,000 BTU per hour, EHD 18 carries 68,000, EHD 23 carries 129,000, and EHD 31 carries 244,000. Which is the smallest tubing size that will serve the load?
  • A natural gas main leaves the meter and runs to tee A, where a branch drops to a 40,000 BTU per hour clothes dryer. It continues to tee B, where a branch drops to a 199,000 BTU per hour tankless water heater, and then continues to a 120,000 BTU per hour furnace at the end of the run. Using a heating value of 1,050 BTU per cubic foot, given, what demand is used to size the section of main between tee A and tee B?
  • A natural gas system is supplied at 7 inches water column, and the design for this project limits the pressure drop in the piping to 0.3 inch water column. The longest run measures 70 feet and the section being sized carries 150 cubic feet per hour. Take these capacities at 70 feet as given data: with a 0.3 inch water column drop, 3/4-inch pipe carries 122 cubic feet per hour and 1-inch pipe carries 230; with a 0.5 inch water column drop, 3/4-inch pipe carries 160 cubic feet per hour and 1-inch pipe carries 300. What size is required?
  • A natural gas capacity table is published for a gas of 0.60 specific gravity. The utility serving this site delivers gas at 0.70 specific gravity, and the multiplier given for 0.70 specific gravity is 0.926. At the design length the table shows 1-inch pipe carrying 285 cubic feet per hour. The connected load on that section is 270 cubic feet per hour. Does 1-inch pipe still serve the load once the correction is applied?
  • A natural gas system is sized by the longest length method, and the most remote outlet measures 118 feet from the point of delivery. A range draws 65,000 BTU per hour and sits on its own branch only 14 feet from the meter. Using 1,050 BTU per cubic foot, the range demand works out to about 62 cubic feet per hour. Take these capacities as given data: at 20 feet, 1/2-inch pipe carries 92 cubic feet per hour; at 125 feet, 1/2-inch pipe carries 34 cubic feet per hour and 3/4-inch pipe carries 71. What size is required for the branch serving the range?
  • An existing natural gas system was sized on a longest run of 60 feet. A 40,000 BTU per hour unit heater will be added at the far end of the shop, making the new longest run 140 feet. The section of 1-inch pipe leaving the meter carries 240 cubic feet per hour today and will carry 278 cubic feet per hour after the addition. Take these capacities for 1-inch pipe as given data: 285 cubic feet per hour at 60 feet, 195 at 125 feet, and 175 at 150 feet. What does the section leaving the meter require?
  • A gas main leaves the meter and runs 46 feet along an exterior wall, rises 14 feet up the wall to a roof penetration, runs 38 feet across the roof, and drops 3 feet into the curb of a rooftop unit. What developed length is used to enter the sizing table for that run?
  • A house will be served by a 100,000 BTU per hour furnace, a 199,000 BTU per hour tankless water heater, a 65,000 BTU per hour range and a 40,000 BTU per hour clothes dryer. Take the heating value as 1,000 BTU per cubic foot and the rating of the existing meter set as 400 cubic feet per hour, both given. What is the correct finding?
  • A 3/4-inch gas main runs across a shop ceiling. A drop 12 feet long is taken from it to a unit heater rated 75,000 BTU per hour, whose gas inlet is tapped 1/2 inch and whose listed connector is 1/2 inch. The longest run in the system measures 95 feet. Take the heating value as 1,000 BTU per cubic foot and these capacities at 100 feet as given data: 1/2-inch pipe carries 40 cubic feet per hour, 3/4-inch pipe carries 82 and 1-inch pipe carries 155. What size is required for the drop?
  • A propane system serves appliances totaling 220,000 BTU per hour. Take these values as given data: propane has a heating value of 2,500 BTU per cubic foot and natural gas 1,000 BTU per cubic foot. At the design length, the undiluted propane table shows 1/2-inch pipe carrying 131 cubic feet per hour and 3/4-inch pipe carrying 273, while the natural gas table at the same length shows 1/2-inch pipe carrying 73 and 3/4-inch pipe carrying 151. What size is required?
  • A branch serves two appliances. The boiler nameplate reads 180,000 BTU per hour, and the submittal for the make-up air heater gives its input as 96 cubic feet per hour. Take the heating value as 1,050 BTU per cubic foot, given. What total demand is used to size the branch?
  • A gas-fired boiler rated 199,000 BTU per hour and a water heater rated 40,000 BTU per hour share a closet that takes all its combustion air through one permanent opening communicating directly with the outdoors. Take the single opening method as given data: 1 square inch of free area for each 3,000 BTU per hour of total input. What minimum free area does that opening require?
  • A boiler nameplate shows an input rating of 200,000 BTU per hour and an output rating of 160,000 BTU per hour. A water heater on the same branch shows an input rating of 76,000 BTU per hour. Take the heating value as 1,000 BTU per cubic foot, given. What demand is used to size that branch?
  • An electrician proposes to connect a grounding electrode conductor to the interior black steel gas piping of a building. How does the fuel gas code treat the use of gas piping for that purpose?
  • A gas range stands against a partition, and the shutoff valve serving it was roughed in on the far side of that partition inside a base cabinet. The installer proposes to run the listed flexible appliance connector through a bored hole in the partition to reach the valve. How does the fuel gas code treat that arrangement?
  • A combustion air opening has been sized correctly for the free area the appliances require. The architect asks that it be built as a long, narrow slot 2 inches high so it can be concealed in an architectural reveal. What limit does the fuel gas code place on the proportions of that opening?

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