The Furnace Filter Whistle alerts you when it is time to replace the filter in the central air conditioner or furnace. The whistle is comprised of two plastic pieces that are snapped onto the filter. A clean filter allows air to move more freely through the filter material. As time progresses, dirt and dust build up, forcing more air through the filter whistle. The build-up leads to a steady, audible sound produced by the whistle. The sound alerts you that it is time to have the filter changed.
Once the dirty filter has been removed, the furnace filter whistles can be reattached to the new one. Make it a priority to regularly change the filters results in increased efficiency of the heating and cooling system, which can extend the life of the units as well as save money on energy costs.