Does anyone know if there are registers (the outer frame is 24"x24" used with 24"x48" ceiling tiles) that have a changable filters? I know that they could not be very dense filters due to fact that they would block airflow. After getting a look inside the ac and the vents at work, I think I found out why everyone here is stopped up and sneezing/eyes burning etc... Thankfully, the management is going to replace this (frankenstien with components older than me)system and ductwork, but not for a couple of months. I thought if I could find a replacement register with a filter, it may help some. Im sure I will end up with making my own cut to size and taping it in.