How do you properly install an air filter in a furnace?

To properly install an air filter in a furnace, first turn off the furnace and locate the filter slot. Remove the old filter and make sure the new filter is the correct size and type for your furnace. Insert the new filter with the airflow arrow pointing towards the furnace. Secure the filter in place and turn the furnace back on. Check the filter regularly and replace it as needed to maintain proper airflow and efficiency.