We recently purchased a home with the above A/C unit installed. As we don't know when the filter was last changed, we want to install a fresh one now. It currently has a filter #FILCCFNC0024 Merv 8 installed. These are not readily available at Home Depot, etc and seem to be quite pricey in researching this filter number online. I tried finding a user manual online to no avail. Is this the only type filter I can use in this unit? Any and all help with this issue would be greatly appreciated.