This reductor fits onto the hot air side of the Planar 44D. It does NOT fit the fresh air side.
Please note, that a 75mm air duct system is only advisable for smaller systems, e.g. with overall length of <1mtrs. With increasing air flow resitance the heater may eventually not be able to transport the full 4000W with the available flow and shut off due to overheating.
For best use of the heaters capabilities, aswell as for larger and more complex systems we recommend using the 90mm adaptor and fitting a 90mm hot air system.