The Energy Performance Score: MPG for Houses

So, you want to buy an energy-efficient house? Terrific, but how do you know which house actually is the most energy efficient? This is one of the biggest obstacles to buying “green.”

When you buy a car, you can compare the gas mileage estimates for two or more cars; you know how much fuel each car will consume. Now EarthAdvantage, a non-profit in Oregon, and Energy Trust of Oregon have developed a MPG for houses: the Energy Performance Score.

The Energy Performance Score (EPS) is calculated following an energy audit of a home. The score is based on a home’s shape, size, insulation levels, air leakage, heating and cooling systems, major appliances, lighting, and hot water heating. Occupancy, behavior, indoor temperature, and regional weather are standardized to calculate normal energy use. A home’s actual energy use will vary with the behavior of the owners, weather, and other factors.

The EPS also includes a carbon score is based on the greenhouse gas emissions for the annual amounts, types, and sources of fuels used in the home. For electricity, the carbon emissions are based on electricity consumed and the mix of sources used by the serving utility. For natural gas, heating oil, and propane, carbon emissions are based on the therms or gallons used in the home.

Following the audit, each house receives a score sheet that depicts energy use and carbon emissions and compares them to local averages. The score sheet also compares each house to local goals for energy use and gives suggestions for improving energy efficiency.

In developing the EPS metric, researchers sought to meet the following criteria:

• Easily understood by the general public
• Meaningful in different contexts to respective stakeholders
• Applicable to new and existing homes so comparisons can be made between homes
• Useful for indicating progress toward individual and community energy goals
• Helpful to homeowners as a baseline against which to evaluate their own energy use
• Consistent over time

By providing consumers with information on homes that do better than the minimum building requirements, standards and labeling can help overcome obstacles and advance building efficiency. Homeowners, municipal governments, utilities, and the real estate industry need an easy-to-understand means of comparing the performance and impact on climate change in both new and existing homes.

The EPS system has caught the attention of energy agencies and legislators around the country. Not only can it make a building-to-building or home-to-home comparison easier, but it can also make the score publicly available on the Multiple Listing Service (MLS).

If it becomes part of the public property records, the EPS will offer an apples-to-apples means of comparing energy performance among homes, and a motivation for homeowners to make needed energy upgrades that can increase the value of their homes. A post-improvement audit can also measure the effectiveness of upgrades, a useful tool for gauging results of stimulus funding for retrofits.

EPS is currently rolled out on a voluntary basis for new homes in Oregon through the Energy Trust of Oregon, and in a 5,000-home pilot in Seattle for existing homes by Earth Advantage Institute.

Image courtesy of james.thompson