Three of four air purifiers with published brand pages state a CADR, and the Dyson page gives no CADR at all. CADR is the clean air delivery rate, and the stated figures run from 230 to 300 cubic metres per hour.
The Central Pollution Control Board (CPCB) National Air Quality Index table describes the Very poor band, an index of 301 to 400, as possibly causing respiratory illness on prolonged exposure.
Its Severe band, 401 to 500, is described as possibly causing respiratory effects even in healthy people. The Arthapedia page of the Indian Economic Service agrees on the six categories and says the index covers eight pollutants.
Two of the four models are from Philips, and the others come from Dyson and from Xiaomi under its Mijia line. A bedroom purifier works on the air inside one room, so the questions that matter are how the rating is stated, what the filter is made of and how loud the unit is at night. Philips India defines the task of a purifier as lowering airborne particles in the home, such as dust and pollen.
Reading CADR and room size claims
A unit may not reach its rated output under all circumstances, as per the EPA guide to air cleaners. Brand pages then fill the gap with coverage claims of their own, and some of those claims differ within the same page.
The Philips AC0951 page headlines a coverage of 30 sq m and later lists a maximum room size of 65 sq m for the same unit. Both figures sit beside a stated CADR of 250.
Xiaomi gives a headline of 400 sq ft for the Mijia Smart Air Purifier 4 Compact.
Its own formula divides CADR by a ceiling height of 2.4 m and 2 air changes, and the result is about 48 sq m for the stated rating.
The Philips AC1711/61 page gives no coverage figure. Dyson says its purifier was tested in an 81 cubic metre room, and the page states that the CADR measure does not reflect performance in a real room.
Among the three stated figures, the Mijia sits lowest and the AC1711/61 highest. Dyson cannot be placed in that order, since the brand gives no airflow figure.
Ceiling height is one of the two inputs in the Xiaomi formula, so a bedroom with a different ceiling would give a different area. Measuring the floor area and ceiling height of the bedroom gives the figures against which each of these claims can be read.
Filter layers and ozone
The Philips AC0951 page lists HEPA, active carbon and a pre filter, and the Mijia page lists a pre filter, HEPA and activated carbon. Dyson says its unit uses a sealed HEPA H13 standard with activated carbon.
Philips describes no filter layers for the AC1711/61 on its page, so that model cannot be compared on this point. In addition, the EPA guide says air cleaning alone cannot remove all indoor pollutants.
Ozone is the other point on a feature list. The EPA guide says ozone has little effect on most indoor contaminants at public health standard levels, and a buyer who meets an ozone function on a listing will find the guide’s warning on generators in the FAQ below.
Noise, filter life and placement
The EPA guide says noise may be a problem with portable air cleaners that contain a fan. For a bedroom unit, the decibel figures on a product page carry more weight than the CADR.
Sleep mode appears on the Philips AC0951 and Mijia pages, and Dyson lists a night mode. Xiaomi gives a decibel figure for sleep mode only, along with a power rating of 27 W. Philips highlights noise claims for the AC0951 that its specification table does not show, and the AC1711/61 and Dyson pages state no decibel level.
On filter life, Dyson says the filter is replaced every 12 months. The Mijia and AC1711/61 pages state no filter life.
Placement is covered in the Philips India explainer, which suggests keeping a bedroom unit about one metre from the bed and away from the wall. It adds that the inlet and outlet need a clearance of 15 to 20 cm around them.
Four models in brief
The picks below follow the order of the table above. Warranty terms are the one printed detail that separates them in a plain way: the Philips AC1711/61 page shows a single term, the AC0951 page shows two terms that disagree, and the Dyson and Mijia pages state none.
PM2.5 readings are described for the Philips AC0951 and Dyson units. The CPCB table also gives 24 hour bands for PM2.5, the same pollutant that these two sensors report, and app control is listed for the AC0951 and the Mijia.
Philips AC0951 suits a bedroom buyer who wants a compact unit with a PM2.5 sensor, app control and a sleep mode. The specifications list a maximum draw of 23 W and a standby draw under 2 W.
A buyer weighing it against the Mijia will find that both list HEPA and carbon with a pre filter, and that both carry a sleep mode.
The AC0951 page also carries conflicting claims. It gives two warranty terms, 2 years and 3 years, and its highlights list noise and virus claims that the specifications do not show.
Philips AC1711/61 suits a buyer who wants a mid size Philips unit with a stated CADR of 300 and a warranty term printed on the page.
The specifications give dimensions of 273 x 273 x 486 mm and a warranty of 2 years.
Room coverage, decibel level, filter life and power are missing from that page. Those specifications would need confirming with the brand before any comparison with the other three.
Dyson Purifier Cool suits a buyer who wants a sealed HEPA and carbon unit with PM2.5 readings in real time and a night mode. Such a buyer accepts a brand stated test room in place of a CADR.
The Dyson page states no model number, airflow figure, decibel level or warranty term. It repeats that CADR does not reflect real room performance, and it offers the 81 cubic metre test room as the measure in its place.
For a single bedroom, the Mijia 4 Compact (model AC-M18-SC) offers Xiaomi Home app control and a sleep mode. Xiaomi states a rated particle CADR of 230 as a brand claim, and the main product page is the only place where that figure is read clearly.
Xiaomi lists the unit at 27 W in its specifications. Among the four pages, only the Mijia specifications give a decibel figure for sleep mode. The coverage formula on the same page does not match its headline, and the page states no filter life or warranty.
