How we decide

• The same rules apply to every product in a category.
• Every number links to its source: public test data or the maker’s own documents. We have not tested these products ourselves.
• If a number isn’t published, we write “Not published”. We never estimate.
• We earn a commission from some links. It never changes a verdict or the order of results.
• A person reviews every page design, and every page passes automatic checks before it goes live.

How buying guides are built

Used today for: air purifiers.

1. Public test data. We start from lab numbers that makers must report to get certified, such as the ENERGY STAR list kept by the US government.
2. The same rules for every model. Each list answers one question, like a room size or a need, and ranks every model that fits by the number that matters for it.
3. Only lists that add something. A list is published only if it has enough models and its top picks differ from the broader list it narrows.
4. Sources on every number. Every figure links to the record it came from, with the date we checked it.