What each rating on the box actually measures, and the replacement questions only the manufacturer can answer.
Filters · explainer
CADR (clean air delivery rate) is how much filtered air a purifier delivers. What the three CADR ratings mean and the EPA minimum for every room size.
Updated 25 Oct 2026
ReadFilters · explainer
A HEPA filter captures at least 99.97% of particles at 0.3 micron. What the definition means, what HEPA cannot tell you about room size, and what to check.
Updated 25 Oct 2026
ReadFilters · explainer
What MERV means on an air filter, why MERV 13 is the line that matters for fine particles, and how MERV 13 compares with HEPA (99.97% at 0.3 micron).
Updated 25 Oct 2026
ReadFilters · explainer
Activated carbon is the filter stage that handles smells and some gases. What it does, why no CADR exists for odours, and how to compare brands.
Updated 25 Oct 2026
ReadFilters · explainer
The pre-filter is the outermost stage, the one catching lint, hair and the visible dust of daily life before any finer media gets involved.
Updated 25 Oct 2026
ReadFilters · explainer
Air change per hour, ACH, turns up in listings as a badge of thoroughness. It sounds like a specification. It behaves like one only sometimes.
Updated 25 Oct 2026
ReadFilters · explainer
True HEPA means the filter meets the 99.97%-at-0.3-micron definition. How to tell it from "HEPA-type" and "HEPA-like" labels, and which number to trust.
Updated 25 Oct 2026
ReadFilters · explainer
PM2.5 means fine particles 2.5 microns and smaller, the figure on air quality reports and home monitors. What it means and which CADR rating covers it.
Updated 25 Oct 2026
ReadFilters · explainer
An ioniser (ionizer) charges particles instead of catching them. What it does, whether it produces ozone, and why it never adds to a published CADR figure.
Updated 25 Oct 2026
ReadFilters · explainer
An ozone generator makes ozone on purpose and calls it cleaning. What it does, what the EPA guide says about ozone indoors, and what to choose instead.
Updated 25 Oct 2026
ReadFilters · explainer
PM10 is the coarse particle fraction: pollen, dust and the particles you can see. How it differs from PM2.5 and which CADR number on the box covers it.
Updated 25 Oct 2026
ReadFilters · explainer
UV air purifiers promise to kill germs, not just trap them.
Updated 25 Oct 2026
ReadFilters · planned
Intervals are set by the manufacturer, not by any public standard. What the manuals say, what loads the media faster, and how to check.
Updated 25 Oct 2026
ReadFilters · planned
Intervals are set by the manufacturer, not by any public standard. Why carbon exhausts silently, and what a spent filter stops doing.
Updated 25 Oct 2026
ReadFilters · planned
Intervals are set by the manufacturer, not by any public standard. The one filter you can rinse, and the schedule that keeps HEPA alive.
Updated 25 Oct 2026
ReadFilters · planned
Intervals are set by the manufacturer, not by any public standard. What MERV 13 does to a furnace, and the pressure-drop trade-off.
Updated 25 Oct 2026
ReadFilters · planned
Intervals are set by the manufacturer, not by any public standard. How washing changes efficiency, and the drying step most people skip.
Updated 25 Oct 2026
ReadFilters · planned
Intervals are set by the manufacturer, not by any public standard. Lamp output fades long before the light stops turning on.
Updated 25 Oct 2026
ReadFilters · planned
Intervals are set by the manufacturer, not by any public standard. What collector plates actually catch, and when cleaning stops helping.
Updated 25 Oct 2026
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