What happens if you put your furnace air filter in backwards?
If the furnace filter is installed backwards, the fibers won’t properly filter the air which can eventually cause damage to the unit. It also will diminish airflow through the furnace causing it to work harder and use more energy.
Are air filters reversible?
The filter is designed to remove a lot of unwanted debris, but only when installed in a certain direction. If you set your filter up backwards, the normally collective end of the device will not face the air supply. In effect, your filter will help keep debris in the air.
Which direction does the airflow in my furnace?
If you are looking at a furnace filter, find the arrow that indicates the proper air flow direction. That arrow must always face toward the furnace and away from the return duct that carries the air in need of heating or cooling.