As September comes to a close and Chicago-area homeowners start preparing for cooler weather, your HVAC system is about to make an important seasonal transition. After spending much of the summer running your air conditioner, your furnace may soon become the primary source of heating in your home. That makes fall a good time to check your HVAC system, replace your filter, and take a closer look at your air ducts. But does that mean every homeowner needs professional air duct