Air Purifier Guides

The research everyone does before buying an air purifier, done for you — the honest coverage number behind the marketing claim, the filter costs that dwarf the sticker price, and which purification technologies actually work.

CADR vs Coverage Claims: The Honest Number the Box Buries

Every air purifier box carries a square-footage claim, and most of them are technically-true nonsense. A purifier that honestly handles a 250 sq ft bedroom gets marketed as 'covers 1,075 sq ft' — same machine, different arithmetic. The difference is air changes per hour, and understanding it takes two minutes. Those two minutes are the entire skill of buying an air purifier, so here they are.

Air Purifier Sizing: ACH Math Instead of Marketing Math

Air conditioner buyers oversize; air purifier buyers undersize — not through any fault of their own, but because the box told them a 141-CADR machine covers a thousand square feet. The result is the most common complaint in every purifier review section: 'ran it for a week, can't tell any difference.' The machine is fine. The math was fiction. Here's the real version, which is short.

The Real Price Is the Filters: Air Purifier TCO, Computed Honestly

Air purifiers are printers: the machine is the teaser, the consumables are the business. Replacement filters run $20-$180 a year depending on brand, which means over a five-year life the filters usually cost more than the purifier — and the brands know you're not doing that math at checkout. We compute a filter-cost-per-year figure for every unit on this site. Here's how to read it, and the traps it catches.

HEPA, Ionizers, UV, PECO: What Actually Works and What's a Light Show

The air purifier industry has a physics problem: the thing that works — a good fan pushing air through a good filter — is a commodity, and commodities don't support premium pricing. So the category grows technologies with better stories: ions, plasma, photocatalysis, UV. Some are harmless garnish, one famously attracted the FTC's attention, and a few actively emit the lung irritant you bought the machine to remove. Here's the field, sorted by evidence.

Air Purifiers for Wildfire Smoke: What Works When the AQI Goes Purple

Wildfire smoke is what air purifiers are truly for. Allergies are seasonal and dust is cosmetic, but a smoke event parks hazardous PM2.5 outside your walls for days and feeds it through every crack — and a correctly sized purifier really can hold a room at healthy levels through an AQI-300 week. Undersized, it loses the rate war and you smell why. Here's the smoke-specific playbook, including the part where a $60 DIY build outperforms machines at five times the price.