Guides / Updated 2026-07-18
UV light or a better filter: which one do you need?
They get sold as the same product. They are not. One catches dust. The other stops things from living on a wet coil.
What a filter does
It strains particles out of the return air. A better filter catches smaller dust. It also resists airflow if it is too tight for the blower, which is how people ice their own systems trying to be thorough.
What UV does
Installed at the air handler, it exposes the coil and the airstream to ultraviolet light. Mold and bacteria that would colonize a damp evaporator do not get a permanent home. It will not vacuum the attic ducts.
The practical answer
Keep a correctly sized filter and change it. Add UV if the coil grows, the startup smell is musty, or someone in the house reacts when the fan starts. Bulbs are typically replaced every one to two years.