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Honeywell S830 Filter Change Indicator

Filter Flag Indicator indicates need to clean or replace air filters in forced-air heating, air conditioning and heat pump equipment.

Red flag drops into window on fan compartment suction increase, which is caused by filter becoming clogged with dirt.
Can also actuate an indicator light on system panel or special thermostat subbase.
Mounts on downstream side of furnace filter, directly on fan compartment or at a remote location using 1/4 in. tubing.