In regards to filters I use a negative ion/hepa/charcoal filter from Kenmore. It draws air in the bottom and through all filter media and back out to the herp room smelling like a rose.
Mine is fairly large about 18 wide by 18 deep by 30 inches high.
It has 3 settings for the rate of air intake and will filter air borne dust, mites, bacteria and viruses down to .01 microns. The charcoal portion I replace every 3 months other than that there is very little maintenance. When I researched air filters I looked at ease of maintenance and cost of replacment cartridges. With mine if I replace carbon every 3 months I am looking at about $40 per year in cost.
The filter itself is pricey about $400 but it works great and it pays for itself in no time. You can pick on up at Sears they come in 4 sizes mine was the one down from the largest size. My herp room is about 6 - 700 square feet and I have over 30 large boas in there plus other animals. When the filter is on you would not even now I had a small zoo in my basement. People who come into the house cannot smell a thing, plus it does alot of good for the animals.
Kenmore Electronic Air Cleaner and Ionizer Model C347 - 32953 buy it at Sears. It is rated for rooms 23 X 28 X 8 ft and changes the air volume in that sized room over 3 times per hour.
Hope this helps.