Best Alen Air Purifiers (2026)

The 35i is the middle of the range and the one that suits most buyers. This listing pairs it with the Ultimate filter, an H13 HEPA stack with an odor layer described as targeting household odors, chemicals, mold, smoke and dust, which makes it the most broadly aimed filter option the brand sells.

The listing gives two numbers that deserve reading together: a headline coverage of 1,400 sq ft and an ideal room of up to 1,000 sq ft. That gap is honest and useful, because the ideal figure reflects a rate that gives several air changes per hour, while the larger one is a one-change-per-hour claim. A room around 400 sq ft is where it delivers proper allergy-grade turnover.

It costs more than the 25i and less than the 45i, with a cabinet that is not intrusive in a living room. As with the entire line, the real running cost is the filter. The Ultimate tier carries the most media, so check its price before you commit and compare it against the cheaper Essential tier if odor and smoke are not issues. In a typical family room it should sit on a middle speed most of the day, which keeps the fan noise below conversation level while still turning the air over several times an hour. Moving it a few feet from the sofa and away from the television cabinet gives the intake room to work and keeps the exhaust from blowing on anyone seated nearby.

The 25i is the small cabinet of the line, shown here with the Essential filter, which is the plainest tier: H13 HEPA aimed at allergens, dust, viruses, dander and pet fur. The listing claims 99.9 percent capture of particles as small as 0.1 micron, a figure for the media rather than a whole-unit result.

It lists 800 sq ft as the headline area and up to 400 sq ft as the ideal room, so a bedroom or office is the target. Under the two-thirds rule that kind of room wants a CADR of around 270, which tells you the unit works best when it is not stretched.

Compared with the 35i, it gives up size and the odor layer of the Ultimate filter, and in exchange the purchase and filter cost fall. If you want carbon for pets or smoke later, check whether an Advanced or Ultimate filter fits the same cabinet and what it costs, since the listings for the 25i are sold in all three tiers. Keep it a hand-width from walls so that it can pull air. The Essential tier is a sensible starting point for a child's room or home office because its filter is the least expensive to replace, and you can step up to a carbon tier later if a new pet or a smoke season changes the picture. Do not hide it behind a curtain or put it on a thick rug, which can block the lower intake.

The 45i is where the listing is most explicit about sensing: built-in optical sensors continuously detect airborne particles and drive a smart auto mode. For a household that cooks or lives near traffic, a fan that rises and falls with the reading keeps noise low in clean periods and acts when needed.

This version carries the Advanced filter, which adds an activated carbon layer to the medical-grade HEPA described in the listing, aimed at smoke, VOCs, pollution and pet odors. That makes it the pick for someone who needs gas handling but does not want the premium Ultimate tier.

The cabinet is larger than the 35i, so it needs real floor space, and its area claim of 1,900 sq ft is again a one-change figure; a working room is about 600 sq ft. Optical sensors need an occasional wipe to stay accurate. Choose it over the 35i only if auto mode matters to you. Keep the optical sensor window clear when you dust, and do not spray cleaning products near the cabinet, since aerosols can briefly confuse a particle sensor and leave the fan running high for no real reason. In a bedroom, check that the display can be dimmed so the smart features do not become a night light.

The 75i is the biggest cabinet in the range, essential for large spaces up to 2,800 sq ft on its listing. Its high-efficiency fan is the point: a larger fan can run at a low speed in an open room and still deliver useful turnover, which is quieter than running a small unit flat out.

Paired here with the Ultimate filter, it carries the full odor layer the listing describes as working on heavy household odors at the molecular level. That wording is marketing, but the real feature is the larger carbon and HEPA volume, which gives a longer life for kitchens and open-plan living rooms.

It is the most expensive to buy and to feed. Unless you have an open-plan floor, the 45i or 35i will do. If you do, treat 2,800 sq ft as a one-change figure and plan on a room near 900 sq ft for proper air changes. Leave generous clearance around it, since the cabinet is large. A unit this size works best placed along the path the air already travels, such as the edge of a hall between kitchen and living space, and it gains little from being tucked into a corner. Because its filters are the largest in the line, buy replacements ahead of the interval and store them flat in their wrapping so the media is not crushed.