| 摘要 |
Disclosed is a change indicator (30) for a filter (10) for use in a gaseous circulation system, such as a forced air heating and cooling system. The change indicator includes an air impervious patch (32) that is secured to the filter. The portion of the filter media (12) adjacent to the change indicator changes appearance in response to the accumulation of contaminants at a much slower rate than the remainder of the air filter. The accumulation of contaminants progresses inwardly from the region adjacent the periphery of the change indicator towards the region adjacent to the center. Once the appearance of the filter media beneath the change indicator fully changes from periphery to the center, that is an indication that the air filter is in need of cleaning or replacement.
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