Stainless Steel External Inlet Grill Inlet ducting and makeup air The heater can take air for heating (makeup air) from either the heated area (return air) or from outside the boat (fresh air). In most cases, a mixture of both is the best choice. The upper of the 2 x ø 75 mm intake air ducts should be installed to take fresh air from outside and the lower fresh air from inside of the boat. Intake air grills 4411 should be installed into the head of the inlet ducts to preclude foreign objects from entering the heater. Protect the outside grill from splash water, spray, etc. If the intake air will be taken from the same space where the heater is installed, there is no need for the inlet air ducts, but protective grills should be present. There have to be minimum 100 cm2 (16 square inches) ventilation hole in the space where the heater is installed.
