Ceiling cassette A/C units are mounted as the name suggests; in the ceiling. This is most effective in a suspended or floating ceiling where there is room to accommodate the unit. Since cold air falls towards the floor, the ceiling mounting provides exceptional coverage and, provided the fans are powerful enough, a ceiling cassette A/C unit can cover a fairly large room. Being in the ceiling also means that the units are out of the way. Since the condenser is located outside the building, a ceiling cassette A/C unit is exceptionally quiet. Further to this, along with modern technology such as adjustable thermostats and variable speed fans, ceiling cassette A/C units are exceptionally energy efficient. Photocatalytic purification filters can also be used with them to filter the air of pollutants and other harmful particulate, meaning the A/C unit can pull double duty as an air purifier.