CEDAR FALLS - It's an average home in Cedar Falls, a duplex built in 1978 a block off of Main Street, and it has the equivalent of an 8-by-8 inch hole where air whooshes in and out.

Even in more modern, tightly built homes, the small cracks can add up. The tiny vents are found in door frames, window sills, where the foundation meets the house and even behind outlets.

Plugging the holes rarely gets done because it's expensive - not in the equipment, but in the labor. In addition, patching tiny vents not easily seen by the naked eye doesn't have the same appeal as something more tangible, like replacing windows.

"This is an almost impossible sell. It would be thousands of dollars worth of labor. It takes a frickin' truck load of labor," said Craig Ceilley of Ceilley Insulation.

Residents of Cedar Falls who aspire to greener homes are in luck. A gigantic truckload of free labor recently rolled into town in the form of 26 AmeriCorps workers whose only job is to live and preach energy efficiency. Ceilley has helped train them.

In 12 rental properties over three weeks, they have laid 4,500 feet of caulk and worked 200 man hours. They have another 20 properties lined up and plan to expand to homeowners in the rest of Black Hawk County before program funding dries up in September 2010.

AmeriCorps partners with Cedar Falls Utilities to offer free energy audits. CFU already offered them, but previously referred home owners to subcontractors.

If homeowners work through AmeriCorps, they are only expected to co-pay any attic and sidewall insulation, which in this duplex ran less than $100.

"We are saving them a lot of money and making this affordable," said Cortney Schiappa, an AmeriCorps worker who helps coordinate the work.

AmeriCorps members are also picking up some valuable - and unexpected - skills along the way.

Jennifer Betsworth is receiving her master's in historic preservation, which means she will manage old properties of historic value. She can envision using her experience here, where she learned the value of weatherization and how to perform it, in a future job.

"If I ever have to convince people a home is worth saving, now I can say a long time ago I did this really weird job where I insulated doors and windows," she said.