Central and outdoor air conditioning units rely on filters to circulate fresh, clean air throughout the house. Clogged filters can cause your unit to work harder, so it's important to know where to find them. The filter can usually be found along the return duct, on a wall, on the ceiling, or in the unit itself. Many air conditioning systems or hot air heating air handlers, both horizontal and vertical units, have one or more air cleaners installed within the blower assembly.
The filter may be in one or more common air returns or in the air handler, or less commonly, in a slot in the return air duct near the air handler. It is beneficial to have a filter on the air inlets as it helps keep the return ducts and fan clean; however, if you already have a proper air filter in or on the air handler that should protect the fan, you should be careful not to add additional layers of filtration without consulting your HVAC company about the flow rate of your system and ensuring that the air supply through the system is not slowed down. If your building's duct system is so dirty that people are installing extra filters, it may be preferable to have the duct system professionally cleaned. Of course, a heavily soiled air filter will also slow down air movement and increase operating costs in an air conditioning or heating system.
You may see household dust deposits around the edges of the opening where the filter is mounted, indicating where bypass air leaks occur. Different units have slightly different locations, so it is best to consult the drive manufacturer's instructions for your specific unit. Once you have these numbers, head to your local hardware store and you'll find a wide variety of filters. For best results, change the filter every 45 to 90 days, unless you have allergies, pets, or other factors that increase this number.
If you only use a 1-inch filter, there should be a metal divider that prevents significant air intake.
Central airconditioning filters (or heating system filters if hot air heat is also used) can sometimes be difficult to find. Knowing where air filters are normally located can help you find dirty or clogged filters that increase air conditioning or heating costs. Follow the air path and locate the return air; this will tell you where a filter can be placed.
Air handler filters may be located between the return air chamber and other components such as a cooling coil for an AC unit or a heat exchanger for heating systems, as well as a blower fan that causes air to move through these components and out into the supply lines.