It’s 10 p.m.—do you know where your insulation gaps are? As the winter months descend and much of the country braces for icy weather, a startup company in the Boston area called Sagewell is taking it to the streets to let homeowners know exactly where their heating dollars are escaping, and provides suggestions about how to make their homes more energy efficient.

Using special SUV-mounted infrared cameras, Sagewell crews have been cruising the streets of several northern cities at night to take pictures of people’s homes—up to 20,000 on a good night, the company says. The photos captured give a quick assessment of each structure’s thermal envelope and highlight areas where heat is escaping into the outside air. In blobs of color ranging