Put most simply, energy efficiency means that less energy is required to power or fuel a process. As a result, something that is considered energy-efficient could include everything from a vehicle that gets better gas mileage to LED light bulbs that keep rooms bright while using less electricity.
According to Energy Star, energy efficiency can cut energy bills, reduce harmful impacts on climate change, and improve the environment. Not to mention that homes with better energy efficiency often have higher resale values.
Homebuilders, homeowners, and governments use the Home Energy Rating System (HERS) Index to evaluate and measure home energy efficiency. The index is a nationally recognized industry standard that assigns performance scores to homes based on their energy efficiency.
These ratings are conducted by certified RESNET HERS raters, who compare individual homes to reference homes of the same shape and size in similar areas. These raters evaluate several different factors in and outside the home, including:
- All exterior walls (both above and below grade)
- Floors over unconditioned spaces (like garages or cellars)
- Ceilings and roofs
- Attics, foundations, and crawlspaces
- Windows and doors, vents, and ductwork
- HVAC systems, water heating systems, and thermostats
Scores are administered on a scale of 0 to 150 or higher; the lower the HERS Rating, the more energy-efficient the home.
According to data from the U.S. Department of Energy, the typical HERS Index rating for a resale home is 130, which is 30% less energy efficient than a standard new home, which is typically awarded a rating of 100. On the other hand, not all new homes are constructed using the same processes. When homebuilders construct with energy efficiency in mind, new homes can be awarded HERS Index ratings lower than 100.
No home is the same because no piece of land is the same. A builder can construct a single floorplan design in two different locations and the amount of energy needed to power each could be quite different.
For example, a home that receives large amounts of direct sunlight every day will likely heat up faster than homes that receive less direct sunlight each day. Without an efficient HVAC system, the sunnier home would likely require more power to keep it cool. In addition, power costs can be determined by availability, a home’s proximity to power sources, and other factors.
With this said, there are a few standards variables that determine the energy efficiency of a home. In general, the most energy-efficient homes include the following features:
- Tight Construction:Special framing techniques such as continuous air barrier and sealing of penetrations help reduce internal leaks and drafts.
- Improved Thermal Systems: Enhanced insulation techniques help to minimize voids and gaps, and higher thermal properties (R-values) add to energy efficiency.
- Right-Sized HVAC:“Right-sized” heating and cooling systems and sealed air ducts help equipment work together efficiently. “Right-sized” refers to the process of determining which HVAC system should be used in any structure.
- Guaranteed Performance: Written guarantees are issued to homeowners on the amount of energy used for heating and cooling and comfort.
- Low-E Windows:Low “emissivity” windows have protective coatings to help keep heat in during the winter and out during summer.
- Automated Systems:Smart technology found in thermostats and other appliances can "learn" when the house is full and empty and adjust its heating or cooling accordingly, which saves on costly energy use by conserving energy when residents aren't home.
Other common features of energy-efficient homes include fresh air ventilation, combustion safety, pressure balancing, and internal moisture management. To learn how you can maximize your home's energy efficiency, check out this guide.
For the most part, these features can be implemented in used homes. However, high costs associated with installation and renovation can prevent homeowners from updating their preexisting properties. This is one of many reasons why many buyers choose to purchase a new home vs. a used home.