What should I check if the unit begins to whistle after a filter change?

What should I check if the unit begins to whistle after a filter change?

The label sets how the filter is fitted, and a noise or a leak in the system after a change is a matter for the system and the people who run it.

The NanoFlashing™ Air Filter label sets the steps: switch the system off at the thermostat or at the unit's disconnect before opening the filter access; fit the filter into the track with the airflow arrow pointing toward the blower; “Check that the filter sits square in the track with no gap at the frame. Air that passes around a filter is not treated by it.”; then close the access panel and switch the system back on. It also states: “Improper installation can reduce airflow or damage the equipment.” and instructs: “Do not use where this filter would restrict airflow beyond the system's specification.”

The NanoFlashing™ filter has no fan and no moving part; its resistance adds to the pressure the fan works against, and the company publishes no noise measurement. What a particular system does at a particular airflow is decided by that system and by the people who commission it.

Source: NanoFlashing™ Air Filter label, Directions for Use and Caution.

Reviewed on 21 September 2026.