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

120°F (49°C)

Answer

130°F (54°C)

Answer

150°F (66°C)

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

Brass close nipple

Answer

CPVC push-fit adapter

Answer

Standard PEX crimp coupling

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

100 psi

Answer

125 psi

Answer

175 psi

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

Lower initial equipment and installation cost

Answer

Simpler maintenance with no anode rod replacement required

Answer

Significantly lower standby heat loss than direct-fired units

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

Total storage tank capacity of the water heater

Answer

Number and type of plumbing fixtures served

Answer

Incoming cold-water supply pressure at the meter

Question 6

When installing a power-vent water heater, what is the minimum clearance required between the vent termination and a gas meter?

Accepted Answer

3 feet

Answer

1 foot

Answer

2 feet

Answer

5 feet

Question 7

Which statement correctly describes the function of the cold-water expansion tank on a closed hot water system?

Accepted Answer

It absorbs the volumetric expansion of water as it heats to prevent pressure buildup in the system

Answer

It stores reserve cold water for peak demand periods

Answer

It acts as a sediment trap to protect the water heater inlet valve

Answer

It equalizes pressure between the hot and cold water supply lines