Installing an air filter upside down can cause serious damage to your HVAC system and reduce its life expectancy. When efficiency decreases, the likelihood of a system failure, such as a leaking refrigerant line or a faulty compressor, increases. To avoid this, it is important to understand the direction in which an air filter should be inserted in each common type of heating and air conditioning system. When installing the oven filter, look for the airflow arrows printed on the side of the air filter that indicate in which direction the filter should be inserted.
With an upflow oven, the filter will be located near the bottom of the unit, in the fan compartment, next to the cold air return. If the air filter does not have an air flow arrow, make sure the wire mesh faces the fan of the HVAC system, since this is the last surface that touches the air. When the blower draws in air, it goes over the filter, removing dirt, dust, pet dander, pollen, and other particles that can eventually damage the oven. And finally, the air passes through the high-efficiency HEPA filter to trap the smallest particles with an efficiency of up to 99.97%.
Dirty air filters also force the HVAC system to work longer than necessary, reducing equipment life and increasing your energy bills. New homeowners or tenants who don't know their HVAC system well may have problems with this simple step of correctly orienting the filter. Be careful when removing the old air filter, as it has probably accumulated quite a bit of dust and other particles.