Water Heating Efficiency Flashcards
7 cards from real HERS 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 Heating Efficiency flashcards as text
What does the Uniform Energy Factor (UEF) measure for water heaters?
Answer: The overall efficiency of a water heater based on a simulated draw pattern
UEF replaced the Energy Factor (EF) and measures overall water heater efficiency using standardized draw patterns that simulate real household usage.
Which water heater type typically has the highest UEF rating?
Answer: Heat pump water heater (HPWH)
Heat pump water heaters achieve UEF ratings of 3.0 or higher because they move heat from surrounding air rather than generating it directly, making them 2-3 times more efficient than electric resistance units.
In HERS ratings, what is the reference water heater used to calculate the Hot Water Score?
Answer: A standard electric storage heater with a defined EF based on volume
The HERS reference design uses a standard electric storage water heater with an Energy Factor calculated from the tank volume formula established in the HERS Reference Home specifications.
What is 'standby loss' in the context of water heater efficiency?
Answer: Heat lost through the tank walls and pipes when no hot water is being used
Standby loss is the heat that escapes through the tank walls, top, bottom, and connected pipes while the water heater maintains setpoint temperature between draws.
What R-value of pipe insulation is typically recommended for hot water supply pipes to reduce distribution losses?
Answer: R-2 to R-4
R-2 to R-4 pipe insulation on hot water supply lines is the standard recommendation to minimize heat loss between the water heater and fixtures, though local codes may specify exact requirements.
Which factor most significantly reduces the efficiency of a heat pump water heater installed in a small, enclosed mechanical closet?
Answer: Insufficient air volume causing the space to cool excessively and starve the heat pump
HPWHs require adequate air volume (typically 700-1,000 cubic feet minimum) because they extract heat from surrounding air; an enclosed closet quickly cools to the point where efficiency drops dramatically.
Under ENERGY STAR criteria, what minimum UEF must a residential electric storage water heater (55+ gallons) achieve?
Answer: 2.74
ENERGY STAR requires electric storage water heaters with capacities of 55 gallons or more to achieve a UEF of at least 2.74, which effectively mandates heat pump technology at that size.