We purchased 2-75i units, using 1-upstairs and 1-downstairs. due to large open areas from room to room, we are trying to affect areas where we spend most of our day and night. the units are working nicely, but reaffirm that our air quality due to fire smoke is challenging, but machines are improving the overall & we are glad to have them. Our children's households are ALL using the Alen Purifier units of various sizes and are pleased as well.