A dirty filter is the #1 reason for HVAC system failure. A dirty filter restricts air flow into your HVAC systems air handler. If its dirty, it makes your fan motor work extra harder and consume more energy. Easy way to reduce your energy bill is to replace your filter. It also reduces air quality in your home air quality can aggravate allergies and asthma. Especially in kids. make sure to change your filter every 30- 60 days as needed.
It is usually located right next to your furnace or air conditioning system air handler. The air handler is the large box containing the fan and fan motor. The air filter is typically located at the point where the return duct enters the air handler.
Increasingly, air handlers are being installed in attics. This sometimes limited space will require installation of the air filter in the return. The filter is accessed by removing the grate covering the return duct. It is now unusual to have several returns in a house, with an air filter installed in each return.
Many houses have more than one HVAC system. Each system will typically have at least one air filter. You should check each possible location to make sure you have located all of your air filters.