I am an HVAC contractor and can tell you that all of the furnaces/heat pumps should have a filter on the return air side of the unit. If you install additional filters at the return grilles, you must then eliminate the one at the furnace/heat pump. You should not have "double" filtration as the systems are designed to handle a certain amount of static pressure or friction within the ductwork. Adding a second filter will cause too much restriction and could cause problems of insufficient air through the unit. I would only suggest duct cleaning on very old systems or ones that have been run without a filter for a period of time.
|