Designed to operate the fan when the relative humidity reaches a pre-set level.- Comes with a single pattress back box 20mm deep- Adjustable between 20% (always on) and 90% (rarely on) relative humidity.- Integral timer adjustable between 1 and 45 minutes.- Remote humidity sensor for MANHR 4500DC only- This unit is adjustable between 20-90% RH and comes complete with an on/off switch which fits a double pattress- Fits single pattress 20mm deep