Fuel gas: Iowa Journeyperson Plumber Practice Questions

Use 1,000 Btu per cubic foot for natural gas. A furnace is rated 80,000 Btu/h. What gas flow does it need?

Divide the input rating by the heating value of the gas. For natural gas at 1,000 Btu/ft³, CFH is Btu/h divided by 1,000.

Use 1,000 Btu per cubic foot. A house has a 100,000 Btu/h furnace, a 40,000 Btu/h water heater, a 65,000 Btu/h range and a 35,000 Btu/h dryer. What total gas load must the piping carry?

Add every appliance's input, then convert to CFH. Leaving out the dryer gives 205 CFH.

Use 2,500 Btu per cubic foot for propane (LP gas). A 50,000 Btu/h appliance runs on propane. What flow does it need?

Propane has about 2,500 Btu per cubic foot, so the same appliance needs less volume than on natural gas. Using 1,000 gives 50 CFH.

In the longest length method of sizing gas pipe, which length is used to size every section of the system?

With the longest length method, the distance from the point of delivery to the farthest outlet is used for all sections; each section is then sized by the CFH it carries.

Use these capacities for this problem only, at a length of 60 ft: 1/2 inch carries 70 CFH, 3/4 inch 150 CFH, 1 inch 300 CFH. The meter-to-farthest-outlet length is 58 ft. The main serves a 100 CFH furnace and an 80 CFH range. What size is the main?

Round the length up to the next column, add the CFH carried by the section and choose the first size whose capacity is at least that load.

Same system, same capacities at 60 ft (1/2 inch 70 CFH, 3/4 inch 150 CFH). Using the longest length method, what size is the branch serving only the 100 CFH furnace?

Every section uses the longest length, not its own short length, so the furnace branch is sized at 60 ft for 100 CFH.

Which pipe material is NOT allowed for fuel gas piping?

Cast iron pipe is not allowed for gas. Schedule 40 steel, listed CSST and polyethylene (underground, outdoors) are approved.

When may copper tubing NOT be used for natural gas?

Hydrogen sulfide attacks copper, so copper and brass are limited to gas that is low in it (0.3 grains per 100 scf on average); many utilities forbid copper anyway.

Where may polyethylene (PE) gas pipe be installed?

PE gas pipe is limited to outdoor underground use (it may rise above ground only in a listed riser). It is damaged by sunlight and has low heat resistance.

What must be installed with buried plastic gas pipe so it can be located later?

A tracer wire (18 AWG copper minimum, insulated) runs with the plastic pipe so locators can find it.

Under the UPC, what is the minimum cover over underground gas piping where external damage is not likely?

The UPC requires at least 12 inches of cover, increased to 18 inches where external damage is likely. Where 12 inches cannot be provided, the pipe goes in conduit or is bridged.

Where is gas piping prohibited?

Gas pipe may not run inside air ducts, chimneys or vents, clothes chutes, dumbwaiters or elevator shafts.

How may gas piping be installed in a concrete slab floor?

Gas pipe in solid floors runs in channels or in a sleeve or conduit, so it can be protected and replaced; it is not cast directly into the concrete.

Where must the shutoff valve for a gas appliance be located?

Each appliance needs an accessible shutoff valve in the same room and within 6 ft, upstream of the union or connector.

Where is a sediment trap installed on a gas appliance supply?

The sediment trap (a tee with a capped nipple pointing down) catches dirt and scale before they reach the appliance controls.