The cold weather means its time to change your furnace filters, or at least check to make sure they are clean.Heather Kuenster from Kuenster Heating and Air in Kalona tells us that clogged furnace filters can cause a lot of problems. They make your furnace work harder to maintain airflow, which reduces efficiency and can even cause the furnace to shut down. Filters need to be replaced based on their size. A one inch filter needs to be replaced once a month, a two inch filter needs to be replaced every two months, and so on. They also tell us that you should check your filter at the beginning of every winter, even if your furnace hasn’t been on all year.