The air cleaner in your home's HVAC system can be located in a variety of places, depending on the type of system you have. In a vertical upflow system, it is usually found at the bottom, while in a vertical downflow system, it is usually at the top. For horizontal HVAC systems, which are often found in attics, garages, or large basements, the air cleaner is usually placed vertically in a slot on the side of the unit. It is also often close to your home thermostat or in a return duct.
In some systems, filters are located in the return air duct. If you have a large system with multiple air handlers and return ducts, finding the filters can be a challenge. Once you have located the air filters, document their location for future building owners, occupants, or repairers. The edge of most air filters has an arrow showing the intended direction of air flow through the filter. It is important to change the air filters in your air conditioning or heating system every month when the air conditioning system is operating.
If your air conditioner works as a heat pump, you should clean or replace the filter once every three months throughout the year. If your system's air filters are not located near the return vent, they may be in the return air intake grille on the ceiling or wall of the building. If you notice that the fan blades of your air conditioner or heater blower are clogged with dirt (or MOLD), it is important to have a professional thoroughly clean the air handling unit, including the fan blades themselves. In addition to locating and changing your air filters regularly, it is also important to look for any sources of debris near the central air return and any leaks that could lead debris to the return air duct system along any part of its length. This will help ensure that your HVAC system continues to run efficiently and effectively.