Water Heating Systems Flashcards
6 cards from real 306A practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Water Heating Systems flashcards as text
What is the difference between a direct-vent and a power-vent water heater?
Answer: A direct-vent uses sealed combustion with intake and exhaust through the wall; a power-vent uses room air for combustion and a fan to exhaust through the wall
A direct-vent water heater draws combustion air from outside through a dedicated intake pipe and exhausts through an adjacent pipe (sealed combustion). A power-vent uses room air for combustion and a motorized fan to force exhaust gases horizontally through a sidewall vent.
What type of venting material is required for a high-efficiency condensing gas water heater?
Answer: PVC or CPVC plastic vent pipe
High-efficiency condensing water heaters produce cool, acidic exhaust (below the dew point) that would corrode metal venting. PVC or CPVC plastic vent pipe is used because it resists the acidic condensate.
What is the efficiency advantage of a tankless (on-demand) water heater over a standard storage tank heater?
Answer: Tankless heaters eliminate standby heat loss because water is heated only when flowing through the unit
Tankless water heaters eliminate standby heat loss — the energy wasted keeping a tank of water hot 24 hours a day. They heat water only when a fixture is opened, achieving energy factors of 0.82 to 0.96 compared to 0.58 to 0.70 for standard tank heaters.
What is the minimum flow rate typically required to activate a tankless water heater?
Answer: 2.0 L/min (0.5 gpm)
Most tankless water heaters require a minimum flow rate of approximately 2.0 L/min (0.5 gpm) to activate the heating element or burner. Flow rates below this threshold will not trigger the unit.
What maintenance task should be performed annually on a gas water heater to ensure safe operation?
Answer: Inspect the flue and vent connector for proper draft, check the T&P valve, drain sediment from the tank
Annual maintenance includes inspecting the flue and vent connector for blockage or corrosion, testing the T&P relief valve operation, and draining sediment from the tank bottom to maintain efficiency and safety.
What causes 'stacking' in a storage-type water heater?
Answer: Repeated short draws of hot water that cause the top of the tank to reach dangerously high temperatures while the thermostat at the bottom remains satisfied
Stacking occurs during repeated short draws (such as frequent handwashing) where the cold replacement water entering the bottom keeps the thermostat calling for heat, while the already-hot water at the top continues to get hotter, potentially reaching dangerous temperatures.