MARRIOTTSVILLE, Md.  In the basement of Phyllis Fick’s ordinary-looking suburban house, Tim Kenny of C&O Conservation, a nonprofit weatherization company, found black streaks of dirt on the yellow fiberglass insulation, evidence of air infiltration from the window beneath, a sure sign of an energy leak.

Nearby on the basement ceiling, a drainpipe from the bathroom above had spider webs around it, another bad sign. Spiders build near air currents to draw insects to their webs, Mr. Kenny, C&O’s manager, said, and the current probably ran from the basement to the attic, taking heated air with it.

But the “aha!” moment for the C&O team belonged to Brian Kinzer, who put a ladder on the front porch and pulled down the vinyl covering of the underside of the roof overhang. Instead of plywood, he was staring at the bright metal of a heating duct that curved up to the second-floor bedroom of Mrs. Fick’s 18-year-old daughter. The duct had been unprotected from the outdoor temperature since the house was built about 30 years ago.

“Look at this!” Mr. Kinzer said in triumph.

Call it CSI: Thermal Police  energy experts armed with mostly low-tech tools but strong sleuthing skills, finding flaws that let the air inside a house go through a full exchange with the outdoors twice an hour, instead of once every two or three hours.