Breaking down rating systems
With so many rating systems available to help ensure a home’s greenness, it can be hard to keep them all straight. Here’s a quick guide of common rating systems used for homes and water-heating systems:
Energy Factor (EF) – A measurement of the overall energy efficiency of a water heater, which is based on three measurements:
- How efficiently the water heater transfers heat from the heat source to the water
- What percentage of energy is lost from cooling unused, stored hot water—in the case of traditional tank-style water heaters (standby loss)
- How much energy is cycling between active and standby mode uses
A rule of thumb: the higher the EF, the more efficient the model.
Home Energy Rating System (HERS) Index – The industry standard by which a home’s energy efficiency is measured, according to the Residential Energy Services Network (RESNET). It’s also the nationally recognized system for inspecting and calculating a home’s energy performance. Some of the rating’s variables include:
- All exterior walls, both above and below grade
- Floors over unconditioned spaces, such as cellars and garages
- Ceilings and roofs
- Attics, foundations and crawlspaces
- Windows, doors, vents and ductwork
- HVAC systems, water heaters and the thermostat
A rule of thumb: the lower the value, the more efficient the home.
LEED (Leadership in Energy and Environmental Design)for Homes– Developed by the U.S. Green Building Council, this system demonstrates in measurable terms that a home incorporates efficient green homebuilding techniques and features, and that the final product has been third party-verified and performance tested. The rating scale is based on points earned for meeting specific green building conditions, such as specifying energy-efficient tankless water heaters and furnace and boiler systems. Other determining factors include: building and design, location, landscaping, materials and resources, waste management, indoor environmental quality, other water and energy efficiency factors, and awareness and education of the homeowner on basic operations.
A rule of thumb: the higher the LEED score, the more efficient the home.