Guides
Quick answer
These guides cover the measurements behind every recommendation on the site, starting with the one line of arithmetic that decides what a room needs. There are 14 pages in this section.
MOOKA Air Purifier for Home Bedroom Large Room 2200 Ft2, HEPA Filter, Black
A machine with a published specification, which is what makes the arithmetic on these pages applicable to it rather than to a coverage claim with no rate behind it.
Prices and specifications change, so check the listing before buying.
Every page in this section
- Guide
Air changes per hour explained
ACH counts how many times a machine filters a room’s full air volume in an hour. Here are the 2 to 6 targets and the decay math behind them.
- Guide
Air purifier noise levels explained
The decibel figure on the box is almost always the lowest speed. The speed that actually delivers the rated CADR is a different, louder number.
- Guide
Air purifier running costs: power and filters
Electricity for a purifier is usually the smaller cost. Here is the watts-to-dollars math at a stated rate, plus what filters actually add per year.
- Guide
Do air purifiers actually work?
The honest, measurable answer: they reduce airborne particulate concentration in the room they sit in, at a rate you can calculate from CADR and room volume.
- Guide
How HEPA filters actually work
HEPA media catches particles with three separate mechanisms, and the hardest size to catch is 0.3 micron, not the smallest particle that passes through.
- Guide
How often to change an air purifier filter
Manufacturer intervals assume average use. Household dust, pets, and smoke exposure all shorten the real interval a filter lasts.
- Guide
How to read an air quality monitor
PM2.5, CO2, and VOC index each measure something different. Here is what a cheap sensor can tell you, and where its numbers stop being reliable.
- Guide
How to size an air purifier for a room
Measure floor area and ceiling height, pick a target air change rate, then solve for CADR. Here is the full method end to end with real numbers.
- Guide
Ideal indoor humidity levels
30 to 50 percent relative humidity is the target range indoors. Above 60 percent supports mould and dust mites; cold weather adds a condensation ceiling.
- Guide
MERV ratings explained
MERV comes from ASHRAE 52.2 and three particle size bands. The number on the box is the filter’s worst-case result, not its average.
- Guide
Ozone and ionizers: what to know before buying
Ozone generators and some ionizer or plasma modes produce ozone in occupied rooms. Here is which technologies do it, what CARB regulates, and what to switch off.
- Guide
Washable versus replaceable air purifier filters
A washable pre-filter is not a washable HEPA filter. Here is the actual difference, and why a "permanent HEPA" claim deserves a closer look.
- Guide
What CADR actually measures
CADR is a sealed-chamber test under AHAM AC-1, not a room rating. Here is what the three numbers mean and how they translate to your floor plan.
- Guide
Where to place an air purifier
A correctly sized purifier in the wrong spot underperforms its own CADR rating. Clearance, short circuiting, and doors explain most of the gap.
Equipment that comes up most often here
- MOOKA
MOOKA H13 HEPA Air Purifier for Home Pet Large Room Up to 1300ft2, Black
- HEPA claimed
- carbon stage
- has a UV lamp
$46.98 Check pricePrices change often - MOOKA
MOOKA Air Purifiers for Home Room up to 1076ft2, True HEPA Filter, B-D02L
- HEPA claimed
- carbon stage
$49.99 Check pricePrices change often - MOOKA
MOOKA Air Purifiers for Home Room up to 1076ft2, True HEPA Filter, B-D02L
- HEPA claimed
- carbon stage
$49.99 Check pricePrices change often - Clorox
Clorox Small Room Air Purifiers for Bedroom Home, True HEPA Filter
- HEPA claimed
$59.95 Check pricePrices change often - Afloia
Afloia Air Purifier for Home Bedroom Large Room up to 1500 Sq Ft
- washable pre-filter
$59.97 Check pricePrices change often
Common questions
How is any of this researched?
From published test standards, published manufacturer specifications and owner reports, plus arithmetic that is printed on the page so you can check it. Nothing on this site was tested in a chamber by us, and no price, image or product identifier here was invented or estimated.
Do these pages recommend ionizers or ozone devices?
No. Ozone generators are harmful in occupied rooms and are never recommended here at any price, which is why California CARB regulates ozone emissions from indoor air cleaning devices. Where an ordinary machine has an ionizing or plasma mode, these pages say it can be switched off and that the filtration is doing the work.
Where should I start if I am new to this?
With the sizing calculator, because the airflow a room needs narrows the field faster than any list of machines. Once you know the number, most of the marketing on a box stops mattering, and the remaining decision is usually about noise and what the filters cost each year.
Are the prices current?
They are rebuilt from live product listings each time the site is published, so they match what things cost when these pages were last built. Prices move often, so check the listing before buying and treat every total here as a budget rather than a quote.