I forgot to mention that the only issue that I have with my gas furnaces is that it dries the air out too well, so I have to run humidifiers in the bedrooms as well as a larger room humidifier in the living room to keep us from coughing all the time and turning into prunes with cracked skin and nosebleeds. There's only so much we can do with drinking water and using good lotions and creams for the skin and ointment for the noses.