The furnace filter airflow arrow must point toward the blower motor, always. It marks the direction air travels, so the dirty side faces the return duct. ...

A thin fiberglass filter can bow into the blower when a dirty filter spikes pressure differential, with the suction force pulling on the frame. The fix is ...

Left-on plastic wrap chokes a new filter, spiking static pressure. This raises the fan’s airflow resistance. The motor strains, current draw heats windings, ...