Master Plumber Exam Water Heaters and Hot Water Systems 3

Question 1

What is the recommended storage temperature for domestic hot water to prevent Legionella bacteria growth, per ASHRAE Guideline 12?

Accepted Answer

140°F (60°C)

Answer

ASHRAE recommends storing water at a minimum of 140°F (60°C) because Legionella bacteria are killed at this temperature, eliminating the risk of proliferation in the tank.

Question 2

What connection fitting is required between a copper supply pipe and a steel water heater nipple to prevent galvanic corrosion?

Accepted Answer

Dielectric union or dielectric nipple

Answer

A dielectric union or nipple provides electrical isolation between copper and steel, interrupting the galvanic cell that would otherwise accelerate corrosion at the dissimilar-metal junction.

Question 3

What is the standard maximum allowable working pressure (MAWP) for which residential T&P relief valves are rated?

Accepted Answer

150 psi

Answer

Standard residential T&P relief valves are rated to open at 150 psi, matching the typical MAWP stamped on residential water heater tanks.

Question 4

What is the primary advantage of an indirect-fired water heater over a direct-fired storage water heater?

Accepted Answer

Faster recovery rate and longer tank life because combustion occurs in the boiler, not inside the tank

Answer

Indirect water heaters transfer heat from a boiler via an internal coil, so there is no combustion inside the tank — this yields high recovery rates and greatly extends tank service life.

Question 5

When sizing a hot water recirculation pump, what is the primary engineering factor that determines pump head requirements?

Accepted Answer

Total pipe length and friction losses in the recirculation loop

Answer

Pump head must overcome the total friction losses along the entire recirculation loop length, so pipe length and pipe sizing are the primary inputs for pump selection.

Master Plumber Exam Practice Test

Master Plumber Exam Practice Test

Master Plumber Exam Water Heaters and Hot Water Systems 3