Product review (5 stars): Quality filter, low cost
You can spend $$$ to have your heating and cooling people come replace your humidifier filter, or you can buy this and do it yourself.

The box has clear instructions and it takes zero intelligence.  It's about as hard as cleaning the lint filter in your dryer- the difference is you just toss out the old filter and replace with the new, obviously.  From start to finish, it takes about three and a half minutes.

You should replace this filter no less often than once a year.