Product review (5 stars): Easy to install
Just bought a house with a filter that has not been changed in years. This one fit perfectly into the aprilaire holder. It suggest changing every year, and I plan on doing just that. When they get old the water does not vaporize. Mine had a big water circle on the floor until I changed the filter. Now I can feel the difference.  I watched a  video on how to install and it took 5 minutes, if that.