I have runny nose & congestion. but i'm not sick. could it be from the cat dander, that got blown about with the heater? i'm allergic, but tried to put cat in other room. i have dust mite bedding.

You are right: You shoukd also try an air purifier and look into a device called critter zone that actually degrades airborne allergens.

Yes: If you are allergic to cat dander then it doesn't matter where the cat is inside the house. Unless you have a hepa filter in the furnace, the dander will be recirculating constantly when the furnace is on. Cat dander can be detected even 2 years after removal of the cat. Solution? Antihistamine-> removal of the cat following by thorough cleaning -> allergist.