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 maximum recommended water heater temperature setting to prevent scalding at residential fixtures?
Answer: 120°F
120°F is the maximum recommended setting to prevent scalding while still providing adequate hot water for household use.
What is the primary purpose of a Temperature and Pressure Relief (T&P) valve on a water heater?
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.
Using the standard heat formula, approximately how many BTUs are needed to raise 40 gallons of water from 50°F to 120°F?
Answer: 23,300 BTU
BTU = gallons × 8.33 lb/gal × ΔT = 40 × 8.33 × 70 ≈ 23,324 BTU.
What is the first-hour rating (FHR) of a storage water heater?
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.
What type of water heater extracts heat from surrounding air using a refrigerant cycle to heat the stored water?
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.
What is the purpose of a dip tube inside a storage-type water heater?
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.
When installing a gas water heater, what is the minimum required clearance between the draft hood diverter and any combustible material?
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.