When 221 hotel guests fell ill at the American Legion's bicentennial event in 1976 with symptoms of fever and coughing, resulting in 34 deaths, scientists were shocked to learn that the infection hadn't come from some outside source but from within the hotel itself—more specifically, from the building's air conditioning system.

Dubbed Legionnaires' Disease as a result of that fatal outbreak, the strand of bacteria behind the Philadelphia epidemic still thrives in some cooling systems today. But it's not the only thing. Moist, dark and virtually impossible to clean, heating, ventilation and air conditioning (HVAC) systems are a known breeding ground for a slew of unwanted organisms, from molds and fungi to any number of harmful microbes.

But all that could change. Research is now under way to test whether copper—a proven antimicrobial agent—can be used in the fabrication of HVAC systems to stop pathogenic bacteria before they find their way into the airstream.

The federal Environmental Protection Agency (EPA) has already declared that, as a touch surface, the red metal is effective in the fight against a number of harmful microbes. Now, in two separate studies funded by the Defense Department,...