Bought two of these and they seem to work well. The box says they cover rooms up to 300 sq. ft. Both of these arrived without the pre-filter though. (There's a permanent filter inside with an inexpensive pre-filter in front that needs to be replaced a couple times a year.) There was a foam piece where the pre-filter should have been. It seems like they're all shipping without the pre-filter since I ordered two units at separate times and both came the same way. If you contact the company, they will send you a charcoal pre-filter that you can cut to size to fit. The number at Hunter is 888-830-1326.