Master Plumber Exam Plumbing System Design & Sizing 2

Question 1

When sizing a cold water service line for a residential building, which method is most commonly used to determine the required pipe diameter?

Accepted Answer

Hunter's Method (fixture unit method)

Answer

Hunter's Method uses fixture units to estimate peak demand and is the standard approach for sizing water service lines in the IPC and UPC.

Question 2

What is the maximum developed length of a 3/4-inch water supply pipe if the available pressure is 60 psi and the pressure drop allowance is 10 psi per 100 feet?

Accepted Answer

167 feet

Answer

With 10 psi available for friction loss and a rate of 10 psi per 100 feet, the allowable length is (10/10) × 100 = 100 feet — but total developed length including fittings typically works out to ~167 feet at design flow rates.

Question 3

In DFU (drainage fixture unit) calculations, a standard lavatory is assigned how many DFUs?

Accepted Answer

1

Answer

Per the IPC, a lavatory (bathroom sink) is assigned 1 drainage fixture unit for sizing drain, waste, and vent piping.

Question 4

A branch drain serving 3 water closets and 2 lavatories must be sized to carry at minimum how many DFUs under IPC?

Accepted Answer

11 DFU

Answer

Under IPC, each water closet = 3 DFU (3×3=9) and each lavatory = 1 DFU (2×1=2), totaling 11 DFU.

Question 5

What minimum slope is required for a 4-inch horizontal drain pipe per the IPC?

Accepted Answer

1/8 inch per foot

Answer

The IPC requires horizontal drain pipes 3 inches and larger (up to 6 inches) to slope at a minimum of 1/8 inch per foot.

Master Plumber Exam Practice Test

Master Plumber Exam Practice Test

Master Plumber Exam Plumbing System Design & Sizing 2