Water Heaters and Hot Water Systems Flashcards
7 cards from real Master Plumber Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Water Heaters and Hot Water Systems flashcards as text
What is the recommended storage temperature for domestic hot water to prevent Legionella bacteria growth, per ASHRAE Guideline 12?
Answer: 140°F (60°C)
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.
What connection fitting is required between a copper supply pipe and a steel water heater nipple to prevent galvanic corrosion?
Answer: Dielectric union or dielectric nipple
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.
What is the standard maximum allowable working pressure (MAWP) for which residential T&P relief valves are rated?
Answer: 150 psi
Standard residential T&P relief valves are rated to open at 150 psi, matching the typical MAWP stamped on residential water heater tanks.
What is the primary advantage of an indirect-fired water heater over a direct-fired storage water heater?
Answer: Faster recovery rate and longer tank life because combustion occurs in the boiler, not inside the tank
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.
When sizing a hot water recirculation pump, what is the primary engineering factor that determines pump head requirements?
Answer: Total pipe length and friction losses in the recirculation loop
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.
When installing a power-vent water heater, what is the minimum clearance required between the vent termination and a gas meter?
Answer: 3 feet
Power-vent terminations must be at least 3 feet from gas meters to prevent combustion exhaust from creating an ignition hazard or interfering with meter operation.
Which statement correctly describes the function of the cold-water expansion tank on a closed hot water system?
Answer: It absorbs the volumetric expansion of water as it heats to prevent pressure buildup in the system
Water expands approximately 4% when heated; in a closed system (with a backflow preventer), an expansion tank provides a compressible air cushion to absorb that volume increase and prevent dangerous pressure spikes.