Master Plumber Exam Water Heaters and Hot Water Systems 1 — Questions and Answers
Question 1: What is the maximum recommended water heater temperature setting to prevent scalding at residential fixtures?
- 110°F
- 120°F (Correct answer)
- 130°F
- 140°F
Correct answer: 120°F
120°F is the maximum recommended setting to prevent scalding while still providing adequate hot water for household use.
Question 2: What is the primary purpose of a Temperature and Pressure Relief (T&P) valve on a water heater?
- To regulate incoming water flow
- To release water if temperature or pressure becomes dangerously high (Correct answer)
- To control water hardness and mineral buildup
- To measure the heater's energy efficiency
Correct answer: To release water if temperature or pressure becomes dangerously high
The T&P relief valve opens automatically to discharge water if temperature exceeds 210°F or pressure exceeds 150 psi, preventing tank rupture or explosion.
Question 3: Using the standard heat formula, approximately how many BTUs are needed to raise 40 gallons of water from 50°F to 120°F?
- 14,000 BTU
- 18,500 BTU
- 23,300 BTU (Correct answer)
- 35,000 BTU
Correct answer: 23,300 BTU
BTU = gallons × 8.33 lb/gal × ΔT = 40 × 8.33 × 70 ≈ 23,324 BTU.
Question 4: What is the first-hour rating (FHR) of a storage water heater?
- The time in minutes to fully recover a depleted tank
- The gallons of hot water the heater can supply in one hour starting with a full tank (Correct answer)
- The recovery rate in BTU per hour at a 90°F temperature rise
- The maximum flow rate in GPM at the closest fixture
Correct answer: The gallons of hot water the heater can supply in one hour starting with a full tank
The FHR measures how many gallons of hot water a heater delivers per hour starting with a full, hot tank — the key metric for sizing to peak demand.
Question 5: What type of water heater extracts heat from surrounding air using a refrigerant cycle to heat the stored water?
- Condensing water heater
- Heat pump water heater (Correct answer)
- Indirect water heater
- Tankless water heater
Correct answer: Heat pump water heater
Heat pump water heaters use a refrigerant cycle to absorb ambient heat and transfer it to the water, achieving efficiencies of 200–300% compared to resistance heaters.
Question 6: What is the purpose of a dip tube inside a storage-type water heater?
- To drain sediment from the tank bottom during flushing
- To direct cold incoming water to the bottom of the tank (Correct answer)
- To allow air to escape when the tank is filling
- To circulate water evenly around the heating element
Correct answer: To direct cold incoming water to the bottom of the tank
The dip tube routes cold supply water to the bottom of the tank, preserving hot water stratification at the top where the outlet is located.
Question 7: When installing a gas water heater, what is the minimum required clearance between the draft hood diverter and any combustible material?
- 1 inch
- 2 inches
- 6 inches (Correct answer)
- 12 inches
Correct answer: 6 inches
A minimum 6-inch clearance from combustibles is required around the draft hood diverter due to the heat radiated by exiting flue gases.
Master Plumber Exam Water Heaters and Hot Water Systems 1
What is the maximum recommended water heater temperature setting to prevent scalding at residential fixtures?