Sorry for the delay in answering your question.
I've been under the weather for several days w/sinus infection & inflammation. Unless your house has a HEPA filter, your ac & heating system is not filtering all the allergens, pollutants, etc out of the air. Most large dept stores (WalMart, KMart, etc) all carry some type of HEPA filters which might fit your unit. A/C & heating companies also can order you one ... most are a type of steel mesh which you can simply take out and spray with water to clean. You can also type in HEPA filters on the internet and there are several sites which sell these. Make sure your vacuum also has a HEPA filter. I had one like this for over 13 years. You will also see a large difference in the house (less dust means less housework... yea!). Good luck and if you have any other questions, please ask.