Wisconsin Journeyman Plumber (IPC) Calculations Practice

Use 0.433 psi per foot of water. What pressure does a 10-ft head of water put on the lowest joint of a section under test?

Each foot of water column adds 0.433 psi, so a 10-ft head gives 4.33 psi.

A shower measures 30 inches by 32 inches inside. Use the IPC minimums: 900 sq in of area and 30 inches as the smallest dimension. Does the shower comply?

Both IPC tests pass: area of 960 sq in and a smallest dimension of 30 inches.

Use 0.433 psi per foot of elevation. The static pressure at the street meter is 65 psi. What is the static pressure at a fixture 35 ft above the meter?

Lifting water costs 0.433 psi per foot. Adding the loss instead of subtracting it gives 80.16 psi.

A 40-ft horizontal drain is laid at 1/4 inch per foot. How much total fall does it have?

Multiply the slope per foot by the length. Using 1/8 inch per foot by mistake gives 5 inches.

A 1-1/2-inch fixture drain slopes at 1/4 inch per foot. Use the IPC rule that the fall from trap weir to vent may not exceed one pipe diameter. What is the longest run before the vent opening would drop below the weir?

One pipe diameter of fall divided by the slope gives the longest run; it matches the table distance for this size.

Use 8.33 lb per gallon and 1 Btu per lb per °F. How many Btu are needed to raise 40 gallons of water from 50°F to 120°F?

Heat equals weight times temperature rise. Using 120°F instead of the 70°F rise gives 39,984 Btu.

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 the 45-degree constant 1.414. A stack must jog 16 inches. What is the center-to-center travel between the two 45-degree fittings?

Multiply the offset by 1.414 for 45-degree fittings.

A 3-story DWV stack is filled with water to the top of a vent 28 ft above the building drain. Use 0.433 psi per foot. What pressure acts on the building drain joints?

The bottom joints carry the whole column of water. Testing the full height at once puts more pressure on the lowest joints than the 10-ft minimum.

Size a hydromechanical grease interceptor by sink volume. Use these values: a 3-compartment sink, each compartment 18 × 18 × 12 inches; 231 cubic inches per gallon; 75% fill; 1-minute drain time. What flow rate should the interceptor handle?

The sink's full volume in gallons times the fill factor, drained in one minute, gives the design flow. Forgetting the fill factor gives 50.49 gpm.

Use 0.433 psi per foot. A gravity water tank's water level is 92 ft above a ground-floor fixture. What static pressure does the fixture see?

Multiply the height of the water above the outlet by 0.433. Dividing by 0.433 instead gives the wrong 212.47.

A 4-inch building drain runs 66 ft at 1/8 inch per foot. What is the total fall in feet and inches?

One-eighth inch per foot over 66 ft is 8.25 inches. Using 1/4 inch per foot gives 16.5 inches (1 ft 4.5 in).

Use the IPC rule that a vent must be at least half the diameter of the drain it serves, never less than 1-1/4 inches. What is the minimum individual vent for a 3-inch water closet drain?

Half of 3 inches is 1-1/2 inches, which is above the 1-1/4-inch minimum.

Use gph = Btu/h input × efficiency ÷ (8.33 × ΔT). A 40,000 Btu/h gas water heater is 80% efficient and raises water 90°F. What is its recovery rate?

Use the output (input times efficiency). Forgetting the efficiency gives 53.35 gph.

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 the 22-1/2-degree constant 2.613. A drain must offset 10 inches with 22-1/2-degree fittings. What is the travel?

Flatter fittings need a longer travel: 2.613 for 22-1/2 degrees versus 1.414 for 45 degrees.

Use 0.433 psi per foot of water. A 5 psi air test equals about how many feet of water head?

Divide pressure by 0.433 to get feet of head. That is why 5 psi of air is a little stricter than a 10-ft water head.

Use these values for an assembly space: occupant load 300, split evenly between men and women; 1 water closet per 75 women required. How many water closets are required for women?

Split the occupant load in half, then divide by the ratio. Using the full 300 gives 4, a common mistake.

Use these values: street static pressure 60 psi; elevation of the highest fixture 20 ft (0.433 psi/ft); meter and backflow device losses 12 psi; minimum pressure needed at the fixture 15 psi; developed length 150 ft. What friction loss per 100 ft can the piping use?

Subtract elevation, device losses and the required residual from the static pressure, then spread what is left over the developed length. Not dividing by the length gives 24.34.

A slope of 1/4 inch per foot is about what percent grade?

A foot is 12 inches, so 1/4 inch per foot is 0.25 ÷ 12, about 2%. Codes often write it as 2 percent.