The culprit that smells up your home through your chimney is creosote. Creosote is a natural byproduct of burning fuel, especially wood. When the weather is humid and warm, the creosote odor gets stronger. Of course, chimney cleaning will resolve much of the smelly chimney problem, but not always completely. Odor neutralizing agents like baking soda or kitty litter put into the fireplace can help, but many times a deodorizing agent needs to be spread into the chimney.
Sometimes ventilation fans can be installed to reduce these problems. The fact that you have these odors may also indicate that your venting system is drawing too much air down the chimney (downdraft) or that your damper may be defective. There are also several structural defects that can show up as a smelly chimney, so as always we advise a thorough inspection to determine the root cause.