Master Plumber Exam Water Heaters and Hot Water Systems

Question 1

What is the maximum recommended water heater temperature setting to prevent scalding at residential fixtures?

Accepted Answer

120°F

Answer

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?

Accepted Answer

To release water if temperature or pressure becomes dangerously high

Answer

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?

Accepted Answer

23,300 BTU

Answer

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?

Accepted Answer

The gallons of hot water the heater can supply in one hour starting with a full tank

Answer

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?

Accepted Answer

Heat pump water heater

Answer

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.

Master Plumber Exam Practice Test

Master Plumber Exam Practice Test

Master Plumber Exam Water Heaters and Hot Water Systems