The HRQ-PRE-P-HDE circular electric duct preheater is designed for installation on the air intake duct in ventilation systems equipped with an Alnor series recuperator, in a ducted version. The pre-heater acts as an additional, optional protection of the exchanger against freezing and allows balanced operation of the air handling unit even during severe frosts. The heater casing is made of galvanised sheet metal, the heaters of stainless steel. The heaters are equipped with a double protection thermostat - the first one switches on when the temperature exceeds 60oC (automatic deactivation), the second one when the temperature exceeds 90oC (manual deactivation through a reset button), EPDM rubber gaskets on the connection nipples and a 2mb connection cable to the recuperator. We advise fitting a filter in front of the HRQ-PRE-P-HDE to prevent fouling of the heaters and to prolong the life of the product.