Changing a furnace filter regularly will improve your heating in the winter and your air conditioning in the summer.

The filter on the left is clean and new. If your air system is working properly, then your filter will look like the dirty, used one on the right. Douglas Sacha / Getty Images ...

When you should replace your furnace filter. It's a smart idea to check your filter every month, especially during the colder months or any time you're using your system heavily.If it's full of ...