In general, it is recommended to have an air filter on each return grille for optimal air quality and to protect your HVAC equipment from dust, pollen, pet dander, and hair. The filter should be placed in the return vent near the return bank connection on the air handling unit. This will keep the air clean and remove particles that lead to poor air quality. If you don't like the look of return vents, you can purchase decorative grilles that can improve the appearance without obstructing the flow of air.
Alternatively, you can place a filter in the return air duct just before it enters the air conditioner. This is a great way to avoid using return ventilation filters and still keep dust from accumulating inside the return air duct. The size of the return air vent is in direct correlation with the amount of return air needed by the heat pump. Your HVAC system will likely have a filter built into the system itself, but many homeowners are starting to install return air filters in their home's ventilation grilles as well.
This ensures that the air entering the heat pump system closely matches the temperature shown on the thermostat. If your air conditioner is working properly, you're more than ready for a return vent filter upgrade. Some people want to filter more dust and are thinking about putting filters in their AC return grilles. A good central air conditioning system has return ventilation in each room to precisely control the temperature of each room and maintain the same air pressure in each room.