this is a serious problem for many people not just copd sufferers, the only solution I have found is to install a ductless heat pump, theese units do not intake outside air and thus do not suck in pollution, they cost about the same as any other heat pump and are more effecient and are easy to maintain, and there are no duct lines to create more air problems, mine was made by Mitsubishi, it has literally saved my life.