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Fuel Gas Piping — Plumber Practice Questions

53 questions · 8% of the Plumber exam

Worked questions

1. Which appliance connection requires a sediment trap in the gas supply piping when a trap is not built into the appliance itself?

  • AA domestic clothes dryer

    Clothes dryers appear on the code's exception list, so no sediment trap is required at that connection.

  • BA residential gas range

    Ranges and cooktops are specifically excepted from the sediment trap requirement in the fuel gas code.

  • A storage-type gas water heater
  • DAn outdoor gas grill

    Outdoor grills are on the exception list along with other outdoor and decorative appliances.

Why C is correct

Water heaters are not among the appliances the code exempts, so a sediment trap must be installed unless the manufacturer built one into the appliance. The trap gives pipe scale, mill dust and moisture a dead-end pocket to drop into instead of letting them reach the gas control valve and the burner orifice.

What this question is testing

This checks whether you remember which appliances the code exempts from the sediment trap requirement, and whether you understand that the exemption list is short and specific.

On the job

A sediment trap is just a tee with a capped nipple hanging below the run, and it costs a few dollars, but it is one of the most commonly written-up items on a water heater or furnace change-out. Field crews sometimes install it horizontally coming off the side of the tee, which does nothing, because the pocket has to hang below the flow path for gravity to work. New black pipe carries a surprising amount of cutting oil and mill scale, which is why the trap matters most on brand new piping.

Memory technique

Range, dryer, grill get a pass; heaters and furnaces get the trap.

Exam tip

Memorize the short exception list. Anything not on it, especially water heaters and furnaces, needs the trap.

Where to look it up

Drips and sediment traps are IFGC Chapter 4, Section 408. UPC jurisdictions handle this in UPC Chapter 12 or NFPA 54, where the exception list is worded differently, so confirm against your adopted code.

2. A union is needed so a unit heater can be disconnected for service. Where is that union permitted to be installed?

  • AInside the wall chase, so that the finished space stays clear of fittings

    A wall chase is a concealed location. Unions and similar mechanically sealed fittings are prohibited there because a slow leak would go undetected.

  • BAbove the suspended ceiling where the branch tees off the main

    Space above a suspended ceiling is treated as concealed for this rule, so a union is not permitted at that tee.

  • CUnder the floor in the crawl space where the riser turns up

    A crawl space under the floor is a concealed location for fitting purposes, and a union there could weep gas into an enclosed area beneath the building.

  • In the exposed piping at the appliance, downstream of the appliance shutoff valve

Why D is correct

The union is placed where it is exposed and where it is downstream of the shutoff valve. That location lets a technician close the valve, break the union and pull the appliance without disturbing the rest of the system, and it keeps the mechanically sealed joint in view for leak testing at every service call.

What this question is testing

This tests whether you recognize which locations count as concealed and whether you can apply the concealed-fitting prohibition to a real routing decision.

On the job

The practical version of this rule is that everything mechanical happens in the last few feet at the appliance and everything concealed is welded or threaded and fully made up. On a unit heater hung from a ceiling, the union goes after the drop, after the valve, with the sediment trap in the same short assembly. Inspectors look for bushings too, which get used to step a fitting down and are prohibited in the same concealed locations for the same reason.

Memory technique

If you cannot soap it later, do not screw a union there.

Exam tip

Ask whether you could put a soap solution on the joint after the building is finished. If not, the fitting is in a concealed location.

Where to look it up

Piping system installation, including fittings in concealed locations, is IFGC Chapter 4, Section 404. UPC states cover the same ground in UPC Chapter 12 or NFPA 54.

3. A gas line must reach a rooftop unit from a meter located at grade. Which routing is acceptable under the fuel gas code?

  • AInside a return air plenum, provided the pipe is welded steel with no fittings in the plenum

    A return air plenum is a circulating air path. A leak there would be distributed through the entire duct system, so gas piping is prohibited regardless of joint type.

  • BUp the inside of an abandoned masonry chimney flue

    Chimneys and gas vents are named prohibited locations. Abandoning the flue does not change the classification, and the shaft would trap escaping gas.

  • Up the exterior wall of the building, supported and protected against physical damage
  • DUp the elevator hoistway, strapped to the guide rail brackets

    Elevator and dumbwaiter shafts are prohibited locations. They are enclosed vertical shafts with arcing equipment and no way to detect an accumulation.

Why C is correct

An exterior riser is outside every prohibited shaft and duct, so a leak dissipates to open air rather than being carried into occupied space. The code's conditions on that routing are support at the required intervals, protection where vehicles or equipment could strike it, and protection from corrosion, all of which are achievable on a wall.

What this question is testing

This tests recall of the prohibited-location list and whether you can spot that a plausible-sounding qualifier, such as welded joints, does not create an exception.

On the job

Existing chimneys look tempting on retrofit work because the chase already goes to the roof, and crews have been caught doing it. The exterior route is more labor but is what gets approved. Once outside, the details matter: hangers or straps at the code spacing, a coating or wrap where the pipe passes through a wall or contacts masonry, and bollards or a sleeve where a truck could hit the riser at grade. Some jurisdictions also want the riser painted the utility's identification color.

Memory technique

Anything that moves air or moves a car has no business carrying gas pipe.

Exam tip

Ducts, chimneys, chutes and shafts are all off limits. No joint type or condition buys you a way in.

Where to look it up

Prohibited locations for gas piping are in IFGC Chapter 4, Section 404.3. UPC jurisdictions apply UPC Chapter 12 or NFPA 54, which lists similar but not identical locations.

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

    A gauge whose full scale equals the test pressure puts the needle at the very top of the dial, where accuracy is poorest and where a small overpressure pegs it. It fails the 80 percent limit.

  • CA 100 psi gauge, giving plenty of margin above the test pressure

    At 100 psi full scale the test sits at 10 percent of the range, below the 20 percent floor. The needle barely moves off the peg and a real pressure loss can go unnoticed.

  • DA 200 psi gauge, so that the needle can never be driven off the scale

    A 200 psi gauge puts the test at 5 percent of scale, which is worse still. Protecting the gauge from being pegged is not the objective; reading a small change accurately is.

Why A is correct

Dividing the test pressure by the two limits gives the acceptable full scale range: 10 divided by 0.80 is 12.5 psi at the low end and 10 divided by 0.20 is 50 psi at the high end. A 30 psi gauge falls inside that band and places the needle near mid scale, which is where a gauge is most readable and most accurate.

What this question is testing

Whether the candidate can invert a percentage rule to find an acceptable range rather than testing options one at a time, and whether they understand why a test pressure must land in the middle of a gauge's range. It also checks whether they treat the gauge as part of the evidence a test produces rather than as a piece of hardware chosen for convenience.

On the job

Gauge selection is what turns a test from a formality into evidence. On a 10 psi test held for the required time, a 100 psi gauge simply will not show the small drop that reveals a weeping joint, and the inspector will say so. Keep a small gauge in the box for low pressure work and a larger one for high pressure tests, and label them, because the wrong one grabbed in a hurry can cost you a return trip.

Memory technique

Aim for the middle of the dial; a needle at the top or the bottom proves nothing.

Exam tip

Divide the test pressure by each percentage limit to get the acceptable full scale range, then pick a gauge inside it.

Where to look it up

Chapter 4 of the fuel gas code, the inspection and testing section covering test pressure, duration and test gauge requirements. Jurisdictions adopting NFPA 54 have parallel provisions, so confirm what your state has adopted.

6. A section of gas piping must carry 220 cubic feet per hour at a design length of 100 feet. Take these capacities as given data: 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 pound per square inch with a 1.0 inch water column drop, 3/4-inch pipe carries 240 cubic feet per hour and 1-inch pipe carries 450. If the system is converted to the 1/2 pound delivery pressure with line regulators ahead of the appliances, what is the smallest size for that section?

  • A1-1/4 inch, because the 7 inch water column table still governs and 1-inch pipe carries only 175 there

    This is the correct size for the system as it stands at 7 inches water column, but the question asks what the section needs after the conversion. Once the delivery pressure changes, the old table no longer describes the system.

  • B1 inch, because a section carrying 220 cubic feet per hour may never be smaller regardless of pressure

    No size floor attaches to a flow rate by itself. What a pipe will carry depends on the pressure, the allowable drop and the length, which is exactly the set of conditions the tables are organized around.

  • C1/2 inch, because raising the delivery pressure doubles the capacity of every size in the table

    Higher delivery pressure increases capacity, but not by any fixed multiple, and the increase has to be read from the table for that pressure. There is also no listed capacity for that size anywhere near this load.

  • 3/4 inch, because at the 1/2 pound delivery pressure that size is rated for 240 cubic feet per hour

Why D is correct

At the elevated delivery pressure the governing table shows 3/4-inch pipe carrying 240 cubic feet per hour, which covers the 220 the section has to deliver, so 3/4 inch is the smallest size that works. More pressure at the meter means more capacity through the same pipe, which is why elevated pressure systems are the standard answer to a long run.

What this question is testing

This checks whether you can move between capacity tables when the delivery pressure changes, and whether you read the smallest adequate size out of the table that actually describes the system after the change.

On the job

Converting to an elevated pressure system is the usual rescue for a long run or a big tankless addition, and it costs a line regulator, a regulator vent arrangement and sometimes a permit revision, all of which is cheaper than repiping a hundred feet through a finished building. The catch is that appliances rated for low pressure inlet cannot be fed directly, so the regulator placement becomes part of the design.

Memory technique

Push harder, carry more: change the pressure, change the table.

Exam tip

More pressure at the meter buys capacity in the same pipe, but only from the table published for that pressure.

Where to look it up

Capacity tables for elevated delivery pressures and the requirements for line pressure regulators are in IFGC Chapter 4, with sizing in IFGC 402.4. In UPC jurisdictions fuel gas piping is covered by UPC Chapter 12 rather than by the IFGC; the capacity tables trace to the same source but the section and table numbers differ.

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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