To help reduce creosote build-up in your wood-burning chimney system, burn only well-seasoned hardwoods. If you don't know how to build a hot, safe fire, ask your certified chimney sweep for tips on proper wood-burning techniques.
To deter mold, keep indoor humidity low. If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity. Relative humidity can be measured with a moisture or humidity meter, a small, inexpensive ($10-$50) instrument available at many hardware stores.