HomeInOn – Portable air purifiers
Along with a plethora of anecdotal accounts, a variety of government agencies including Public Health Ontario, Natural Resources Canada and the U.S. Environmental Protection Agency, recommend using air purifiers (APs) to reduce particulate matter (such as dust, pollen, dander, smoke and other allergens) and volatile organic compounds (including formaldehyde, vinyl chloride, benzene and ethylene glycol) from household air.
The consensus is that if you suffer from allergies, asthma or other asthma-like conditions, or have multiple chemical sensitivities, an AP may well provide some relief, particularly if used in conjunction with other remedial actions.
Portable APs, designed to be used in homes and offices, aren’t overly complicated devices. They typically consist of a pre-filter that traps large particulate matter; a HEPA (High Efficiency Particulate Air) filter that traps particulate matter; an activated carbon filter that remove odours, chemicals and gases; and a fan that draws air across the filters, releasing cleaned air into the room. In many APs, all three of these filters are combined into a single main filter that makes filter replacement more convenient.
Some APs include additional technologies. However, there is little unanimity on how beneficial these technologies are. Ozone generators use an electrical charge to convert oxygen (O2) into ozone (O3). While ozone may improve the odour of indoor air (only because it deadens your sense of smell) it doesn’t remove particulate matter, carbon monoxide or formaldehyde from the air. And almost all health authorities caution that long-term exposure to ozone is likely to be detrimental to your health. UV lamps sterilize mould spores and bacteria. However, they can also generate ozone, though most often in quantities below the maximum safe threshold of 0.1 ppm (parts per million) over an eight-hour period. Ionizers (a.k.a. negative ion generators) release negative ions into the air that electrically charge particulate matter, causing the particles to collect on hard surfaces like walls and ceilings. But these particles eventually get re-circulated back into the air. Catalytic filters, a technology that is considered safe, break down formaldehyde (a toxic systemic poison) into water and CO2.
There are three broad styles of APs: compact cylindrical (a.k.a. desktop) models best suited for small rooms; larger rectangular or console floor models for large rooms; and tower-style models that are also suitable for large rooms. I tried out three popular AP brands using each over a period of two weeks in a 280 sq. ft. living room.
All three include a main filter that consists of a combined true HEPA filter and activated carbon filter. The HEPA filters capture 99.97% of particles and impurities as small as 0.3 microns. It’s important to note that the filters need to be replaced regularly (about every nine months for the Mila and yearly for the Dyson and Winix) in order for the APs to operate efficiently. Otherwise you’ll simply be recirculating dirty air. The Mila filter, which weighs 2 pounds, 14 ounces, contains 1.96 pounds of activated carbon. The Winix filter only weighs 9.5 ounces, so likely contains a fairly small amount of carbon. The Dyson has two filters (one at the back, the other at the front) for a total weight of 2 pounds, 6 ounces. Like Winix, Dyson doesn’t specify the amount of carbon, but it’s likely somewhat less than the Mila.
Each unit includes a sensor that measures the amount of particulate matter in the air. The Winix reports air quality in general terms via three LEDs on its display panel. The Mila and Dyson have additional sensors that report on air quality through their apps. You get various graphs and data displaying air quality over time for different indices, including micron sizes of particulate matter at 1 micron, 2.5 microns and 10 microns, and levels of VOCs, carbon monoxide and carbon dioxide, along with humidity and temperature.
All three also feature an auto mode that automatically adjusts fan speed in tandem with indoor air quality and a sleep mode that lowers the fan to almost silent speed. Generally speaking, higher fan speeds clean the air more quickly, but emit more noise. At lower speeds an AP needs to run longer to increase the amount of air filtered and operate more quietly. At the 50% or “medium” fan speed the noise level (measured 6′ from the unit) for all three APs is fairly quiet (less than 40dB) making it quieter than a typical refrigerator. At the highest speed all the APs are pretty noisy.
The Winix and Mila are AHAM (Association of Home Appliance Manufacturers) certified and list CADR (Clean Air Delivery Rates) levels. Dyson has its own POLAR (Point Loading Auto Response) testing technique. Bear in mind that both of these are lab-generated tests – which one is more reliable is debatable. The CADR tests filtration speed – how quickly the AP purifies the air in a small, confined room with the AP located in the centre of the room. The POLAR test is conducted in a much larger room with the AP against a wall, more typical of a real home environment, and assesses the ability of the AP to remove harmful particles and gases, and the uniformity of cleaned air throughout the room.
Here are the (left to right) Winix, Mila and Dyson filters. Each of them is replaceable.
Easy to Read
Although this is the Mila display, the other displays show similar information.
Apps Are In
The Dyson and Mila APs have apps that allow the user to control their filter from their smartphone. This is the Dyson app, but the others show similar information.
Dyson Catalytic Filter
The Dyson air purifier is the only one tested that comes with a catalytic filter. It converts formaldehyde into water and CO2 and never needs replacing.
The Dyson filter is the only one tested that comes with a remote control, making it easy to use from anywhere in the room even if your smartphone isn’t nearby.
All of the apps show detailed historical data that the user can use to increase or adjust the performance of their air purifier.
Test them out
I conducted what I think was a practical test to see how quickly each AP responded to particulate matter in the air and how long it took to clean the air. Before running each test I made sure the AQI (Air Quality Index) was approximately 30. I then burned 1″ of an incense stick placed 6′ from the unit.
The Winix responded quickly, taking 2 minutes, 20 seconds to sense the change in air quality, at which point the orange (fair) light came on. After only 7 minutes, 40 seconds the blue (good) light came back on. However, after the incense stick was doused, the AQI measured 186. It took another 146 minutes runtime for the Winix to bring the AQI down to 30. The Mila responded in 4 minutes, 20 seconds. At the end of the burning session the AQI was at 172. It took 89 minutes with the fan running at 77% speed for Mila to bring the AQI back down to 30. The Dyson was the quickest to respond – only 1 minute, 29 seconds. It took 99 minutes, about 12% longer than the Mila, to bring the air back down to the 30 AQI level. However, it ran noticeably quieter than the Mila throughout its cleansing time.
The Winix A231, at under 15″ high, 9-1/4″ wide and only 9 pounds, is compact and light enough to be easily moved from room to room. It’s also the simplest AP to use – plug it in and turn it on. It has a fine mesh pre-filter that covers the main filter and a PlasmaWave ionizer that doesn’t have to be replaced and can be turned off. The ionizer emits about 1.0 ppb (parts per billion) of ozone. Health Canada recommends a maximum exposure limit of 20 ppb. Three LED lights (blue, orange, red) indicate the air quality (good, fair, poor). There’s also a manual mode that enables you to select one of three fan speeds, along with a whisper-quiet night mode. The filter lasts 12 months, but you have to clean it every 14 days for optimal performance.
Mila looks more like a piece of furniture than an AP. Visitors to your home might think it’s a fancy sofa stool. Like the Dyson, it’s meant to be controlled via your mobile device, though you can operate it manually. The base price doesn’t include a pre-filter or main filter; you purchase them separately. You can choose from seven filter types for different home environments and you can control up to 11 Mila APs via the app. Unlike the Dyson, you can’t power the AP on or off remotely. The on/off switch is located underneath the unit. Mila reports both indoor and outdoor air quality based on an AQI of 0 to 300 and displays fan speed. The lower the AQI number, the cleaner the air. A built-in motion detector can sense when you enter the room and reduce air speed. In auto mode you can select from eight different settings. For example, in Quiet mode it reduces fan speed when you’re in the room; in Housekeeping Service it deep cleans the air when no one is in the room and in Sleep mode it turns off the display screen and reduces fan speed during your set sleep time. In manual mode you can only select the fan speed; Mila then calculates a target AQI and how many minutes it will take to achieve that target. You can’t set your own target AQI.
Dyson Purifier Cool Formaldehyde
The Dyson TP09 is a sleek modern-looking unit that is both an AP and an oscillating fan that uses bladeless technology, which makes it surprisingly quiet compared to a conventional fan. It comes with a convenient remote control that you can use to turn the unit on and off, control fan speed (there are 10 settings), oscillate the fan, change direction of air flow (towards the back or front of the unit), and turn auto mode and night mode on or off. Like the Mila, you can also operate the Dyson using an app. I found the Dyson easier to pair to the app than the Mila. I also found the app easier to circumnavigate. Unlike the Mila, which uses activated carbon to trap formaldehyde, Dyson has a built-in catalytic filter that converts formaldehyde into water and CO2. The converter never needs replacing. The Dyson doesn’t report air quality using AQI; it uses a six-level scale (good, fair, poor, very poor, extremely poor, severe). As with the Mila you can also see a variety of data and graphs. It reports both indoor and outdoor air quality. There’s also a convenient timer that lets you run the unit for 30 minutes, 1 hour, 2 hours, 4 hours or 8 hours.
If you don’t need Wi-Fi connectivity, are looking for a low-priced unit that’s easy to use and maintain, and don’t want access to more accurate air quality data, the Winix A231 might fit the bill. On the other hand, if maximum control is your thing, or if you’re a technophile, the Mila is likely to be a better choice. For those who want the flexibility of both remote and WiFi app control, you won’t go wrong with the Dyson.
HEPA and MERV defined
HEPA filters trap the smallest particulate matter, such as pollen, smoke and dander, by pulling air through a super-fine mesh. There are different classes of HEPA filters rated on their ability to capture different sizes of particles. To be classified as a true HEPA filter it has to be able to trap a minimum of 99.97% of particles and impurities as small as 0.3 microns. Bacteria, viruses and VOCs that are smaller than 0.3 microns would pass through the filter. MERV (Minimum Efficiency Reporting Value) is a measurement scale that rates an air filter’s ability to capture particulate matter between 0.3 and 10 microns. All true HEPA filters have a MERV 17 or higher rating.
Other ways to reduce indoor air pollution