This Michigan company’s G-99 air filter gauge indicates when it is time to replace filter media in forced air heating and cooling systems. It monitors filter media loading and provides a visual indication when the filter needs to be replaced.

GeneralAire, P.O. Box 8025, 438000 Grand River Ave., Novi, MI 48376-8025; 248/476-5100; fax 248/349-2366.

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