Filters · timing

When to replace CR box filters

Dates are a guide; the box itself tells you the truth. Watch for these three signs.

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1. Weaker airflow

The clearest sign. If the same fan speed moves noticeably less air, the filters are loaded.

2. A loaded, grey surface

Pull a filter and look — a uniformly grey, dusty face means it's done its job and needs replacing.

3. Slower air-quality recovery

If your room takes longer to clear after cooking or opening a window than it used to, clean-air delivery has fallen.

Plan ahead with the replacement schedule and the reminder tool.

Related guides

guide
Replacement schedule

Plan by home type.

tool
Filter reminder

Estimate the date.

guide
Troubleshooting

Restore airflow.

Frequently asked questions

How do I know my CR box filters need replacing?

Three signs: noticeably weaker airflow at the same speed, a grey loaded filter surface, and slower air-quality recovery after cooking or ventilation.

Is there a fixed lifespan for MERV-13 filters?

Roughly 6–12 months, but it varies with your home and season. Airflow is the real signal — replace when it drops, whatever the calendar says.

What happens if I leave filters too long?

Clean-air delivery falls, the fan works harder and louder, and in damp conditions old filters can smell. Replacing restores performance.