Just purchased a 10 year old home and discovered during the inspection that the air handler is new, but that there is a slot for an electronic air cleaner, but the slot is empty...meaning there is no electronic air cleaner/filter. There is a pleated filter in the ceiling leading to the air handler. Also the HVAC unit is a heat pump, if that matters. My question is whether I need to purchase an electronic filter, or is it okay to leave the space open and just use the pleated filter with a high MERV rating?