The new year will ring in new “green” requirements from the Environmental Protection Agency for heating and air conditioning units that threaten to raise prices and, for the first time, require flammable refrigerants in residential and commercial HVAC units. The new rule has triggered special training requirements for technicians and fire departments as they grapple with dealing with the possibility of HVAC systems catching fire, although testing shows the risk under most circumstances is low.“It’s certainly a unique challenge. We’re trying to balance environmental considerations with fire safety in this particular instance,” said Robin Zevotek, an engineer at the National...