With a litter box in my office, (picture taken from my chair at the desk) for 13 years, I was fed up with the dust. So After a quick google to see what was available I figured I would roll my own. I had already had 2 hepa room air filters on either side that only would do good running on high which was way to much noise. This is not complicated for anyone with some wood working skills, just a box with a hole for the fan and a hole for the filters. Then a means of attaching the filters. You also need some electrical skills to wire the add-on motion sensor to the receptacle and add a wire with a plug.
Filters are a Merv 15 Carrier/Bryant Infinity Replacement Filter http://www.amazon.com/Carrier-Bryant-Infinity-Repl... It is VERY delicate so don't rub it or you can put holes in it. If you do, use some latex caulk or white glue to seal the damage. Update 4/4/16. The Merv15 was a waste of money, it is too fragile, after 5 months I replaced it with a 4" Filtrete 1550 from Loews. I will update this with how long it lasted when I replace it next. It was less than half the cost of the Bryant.
The pre filter is a washable 20x25 from home depot. http://www.homedepot.com/p/Web-20-in-x-25-in-x-1-i...
This filter has rough spots on the plastic grill, so when you build the holder for the filters, make sure you do not rub the 2 filters against each other like I did or you will put holes in the Merv 15 big guy.
I got 2 pre-filters and change them each week, wash the dirty one and it is ready for the next week. Dust in the room is reduce 95%+! Hope that this gives you so inspiration to build one of your own.
A couple of other notes: Fan runs on low, I have the Motion sensor set to 5 minutes and the light makes cleaning the box nice. Cats only took a day to get used to it, no issues and you will know when the kids use the box is you are like me and clean it out often. No data on how long the Merv 15 will last but if I get 6 months out of it I will be happy.
To make one of these with less wood working, a cheap table of the proper size to go over your litter box could be used. I made a box with the idea that having some air between the fan and filter would let the fan start better with less effort on low. Also I wanted to use a larger filter than the 20x20 size of the fan. That said, it will work fine without a box. A simple table with a 20x20 hole in it, fan on top, filters attached to bottom would work well. You can also buy 20x20 filters making this more suited to a normal sized litter box.
Step 1: It's Time to Change the Pre Filter
Since today is Friday and it is time to swap out the PreFilter I figured I would flip the unit over and take a few more pictures.
First is the filters installed, you can see the 4 dry wall screws holding the simple frame over the filter
Second is the frame, as you can see, just scrap wood put together with drywall screws and a brad nailer.
Third is the frame holding the large filter in place. You can also see the damage repair I had to do after the prefilter was allow to slide directly against the Big Filter.