If your home were a car, how many miles-per-gallon would it get? Is it a Toyota Prius or a Hummer? To give consumers answers, the U.S. government is creating a mpg-like label for homes.

Federal agencies are working together to develop such a label for all homes. Currently, new homes seeking the government’s Energy Star label get a HERS rating for energy efficiency. The lower the score, the more efficient.

“We want to motivate people to do retrofits cost-effective to them,” Kathleen Hogan, the Department of Energy’s deputy assistant secretary for energy efficiency, tells Green House.

Such a label is slated to launch this fall after pilot testing in the summer, Logan says. DOE is developing options with the Environmental Protection Agency, the White House and the Department of Housing and Urban Development.

She says the label could spur demand for the rebates that President Obama outlined last week as part of his HomeStar proposal.

The private sector is also promoting energy labels for new and existing homes. The Oregon-based non-profit Earth Advantage Institute has developed the Energy Performance Score, which enables homeowners to compare scores and helps realtors sell the most efficient homes. A score for a new home is shown above.

Its EPS, which has been rolled out on a voluntary basis for new homes in Oregon, is now being tested in 5,000 existing homes in Seattle.

Both Oregon and Washington state legislatures have created task forces to explore whether to mandate energy labeling when homes are listed for sale, according to the Earth Advantage Institute, which has certified more than 11,000 green homes.

“We use EPS information as a marketing tool to help sell our homes,” said Aaron Fairchild, president of G2B Ventures, a Seattle-based real estate investment firm, said in the Institute’s press release.

The EPS, which includes an energy audit, is based on a home’s size, insulation levels, air leakage, heating and cooling systems, appliances and lighting. It also includes a carbon score that is based on the greenhouse gas emissions for the amount and source of fuels used.

“We pointed to energy labeling as one of the top 10 green building trends for 2010,” said Sean Penrith, executive director of Earth Advantage Institute, said in a statement. He said the EPS won first place last month in the energy category at Change.org’s “Ideas for Change in America.”

Readers: What you want such an energy label for your home?