HERS Water Heating Systems 1 — Questions and Answers
Question 1: What does UEF stand for in the context of residential water heaters?
- Universal Energy Factor
- Uniform Energy Factor (Correct answer)
- Unit Efficiency Factor
- Utility Energy Formula
Correct answer: Uniform Energy Factor
UEF stands for Uniform Energy Factor, the current DOE metric that replaced the Energy Factor (EF) for measuring water heater efficiency.
Question 2: Which type of water heater typically achieves the highest UEF rating for residential use?
- Gas storage water heater
- Electric resistance storage water heater
- Heat pump water heater (Correct answer)
- Propane tankless water heater
Correct answer: Heat pump water heater
Heat pump water heaters move heat from ambient air rather than generating it, achieving UEF values of 3.0 or higher — far exceeding other residential water heater types.
Question 3: According to RESNET/ANSI 301, the HERS reference design water heater efficiency is based on what?
- The most efficient water heater available on the market
- Federal minimum efficiency standards for the installed fuel type (Correct answer)
- A heat pump water heater regardless of fuel type
- The average efficiency of water heaters sold in the US
Correct answer: Federal minimum efficiency standards for the installed fuel type
The HERS reference design uses federal minimum efficiency standards for water heaters matching the rated home's installed fuel type.
Question 4: How does insulating hot water pipes typically affect a HERS rating?
- It has no effect on the HERS rating
- It increases the HERS Index by adding system complexity
- It lowers the HERS Index by reducing heat loss in the distribution system (Correct answer)
- It only affects ratings when pipe length exceeds 100 feet
Correct answer: It lowers the HERS Index by reducing heat loss in the distribution system
Insulating hot water pipes reduces standby heat losses in the distribution system, which lowers the HERS Index, indicating better energy performance.
Question 5: What is drain water heat recovery (DWHR)?
- A system that recirculates hot water to reduce wait times at fixtures
- A device that captures heat from draining shower water to preheat incoming cold water (Correct answer)
- A heat exchanger that transfers heat from HVAC exhaust to the water heater
- A method of recovering heat from dishwasher drain water only
Correct answer: A device that captures heat from draining shower water to preheat incoming cold water
DWHR devices capture thermal energy from warm drain water (typically from showers) and use it to preheat cold water entering the water heater, reducing energy consumption.
Question 6: In HERS rating calculations, on what is the daily domestic hot water consumption estimate primarily based?
- Number of bedrooms in the home (Correct answer)
- Square footage of the conditioned area only
- Number of full bathrooms only
- Number of occupants reported by the homeowner
Correct answer: Number of bedrooms in the home
RESNET/ANSI 301 uses the number of bedrooms as a standardized proxy for occupancy to calculate daily hot water consumption in HERS ratings.
Question 7: Which hot water distribution system configuration typically results in the best delivery efficiency in a HERS rating?
- Single-pipe trunk-and-branch system with large diameter mains
- Recirculation system with an uninsulated return line
- Compact distribution system with short runs and small-diameter pipes (Correct answer)
- Long home-run system with maximum pipe sizing
Correct answer: Compact distribution system with short runs and small-diameter pipes
Compact distribution systems minimize the pipe volume between the water heater and fixtures, reducing both wait time for hot water and water wasted while purging cooled water.
HERS Water Heating Systems 1
What does UEF stand for in the context of residential water heaters?