Broan HRVH100SE Air Purifier, Heat Recovery Ventilator w/HEPA Filtration Delivers 50 to 104 CFM of balanced ventilation 5-inch diameter ports use smaller ducts allowing for easy installation Integrated defrost control allows for a fast and easy adjustment of the defrost duration according to climatic zones Electronic wall control with LCD screen included offers 5 operation modes ( Auto, Economic, Continuous, Re-circulate, and Turbo) for optimal performance Removable terminal block to ease wall control connections Blower design gives a ultra-quiet operation at 2.5 son