Checked October 2, 2026 (18:28 KST) against the US EPA "Guide to Air Cleaners in the Home" (page last updated October 1, 2026) and Levoit’s US product pages. We have not bought, used or tested any air purifier or filter for this guide. It does not recommend a product, and it is not health advice.
A "maximum room size" number on the box is a sizing hint, not a promise that one unit covers your whole home. Before you pay, fill in two things: the area you will actually run it in, with the conditions behind the box number — and what the replacement filters will cost you over a year.
Step 1: Measure the space you’ll actually use it in
EPA’s method is simple: multiply the length and width of the area where you intend to run the air cleaner to get square feet, then compare that to the maximum recommended room size on the product packaging.
Write down three more things next to that number, because EPA says each one is worth considering when you size the unit:
- Open floor plan? EPA says you should consider the entire space the air cleaner would serve — not just the corner it sits in.
- Ceiling above 8 feet? EPA suggests considering an air cleaner sized for a larger area.
- Bigger than any one product serves? EPA says you could consider using multiple air cleaners.
EPA also describes portable air cleaners as designed to filter the air in a single room or area, while central furnace or HVAC filters are designed to filter air throughout a home. That’s why "whole home" deserves a second look when the product is a single portable unit.
Step 2: Find the CADR — and know what it covers
EPA’s advice for filtering particles is to choose a portable air cleaner with a clean air delivery rate (CADR) large enough for the size of the room or area you will use it in. EPA publishes a sizing chart for estimation:
| Room area (sq ft) | 100 | 200 | 300 | 400 | 500 | 600 |
|---|---|---|---|---|---|---|
| Minimum CADR (cfm) | 65 | 130 | 195 | 260 | 325 | 390 |
EPA notes the chart is for estimation, the CADRs are calculated based on an 8-foot ceiling, and with higher ceilings you may want a higher CADR.
Three limits worth knowing before you compare boxes:
- CADR is for particles only. EPA says the CADR rating system is for particles only, and that there are no widely used performance rating systems for portable air cleaners or filters designed to remove gases.
- CADR is usually a top-speed number. EPA says the rating is typically measured at the air cleaner’s highest speed.
- Smoke, dust and pollen CADRs differ. EPA says some packaging lists three CADRs, using tobacco smoke, dust and pollen to represent small, medium and large particles; for small particles, it says to look at a high CADR for tobacco smoke.
Step 3: When the room size comes with "ACH", read both numbers
At least one product page gives the room size together with an air-changes-per-hour (ACH) figure. For example, one Levoit US product page we read on October 2, 2026 lists its "Ideal Room Size" as two different areas, the larger one marked "1 ACH" and the smaller one marked "4.8 ACH", and describes the larger figure as changing the air in that room once per hour.
Our reading: the bigger room number and the smaller room number are the same machine described under different conditions. The larger area goes with fewer air changes per hour. So when a box shows one large "up to" area, look on the label, spec sheet or manual for the ACH (or the CADR) that goes with it before you treat it as your room’s answer. (We don’t quote that page’s exact areas or CADR here because its title and its spec list name different model numbers.)
Step 4: Ask about the speed you’ll really run it at
EPA says that, generally speaking, higher fan speeds and longer run times increase the amount of air filtered, and an air cleaner will filter less air if it is set at a lower speed. EPA also says noise levels depend in part on the fan speed setting, and that noise ratings are reported for some portable air cleaners, sometimes on the packaging.
So instead of relying on reviews of how loud a unit "feels", ask the maker’s documents two questions:
- What noise rating does the manufacturer publish, and at which speed?
- At the speed you’d actually leave it on overnight, does the manufacturer state any airflow or room-size figure — or only the top-speed CADR?
Step 5: Price the filters, not just the box
EPA says all filters need regular replacement, and that if a filter is dirty and overloaded, it won’t work well. That makes filters a running cost, so put them in the budget before you check out.
Here’s what one official filter page shows, as an example of the four facts to separate. On October 2, 2026, Levoit’s US page for the "Core 300-P Replacement Filter 2-Pack":
- Compatibility: says it is a genuine replacement filter for Core 300-P / 300S-P.
- Pack size: lists "2 Pack x Levoit Core 300-RF Original Filter" under What’s Included.
- Interval: says "Recommended replacement every 6–8 months."
- Price: shows a regular price of $54.99 (US store, US dollars) — for the 2-pack, not per filter, and before any tax or shipping at checkout.
That interval is the maker’s recommendation, not a guaranteed filter life; how fast your filter gets dirty depends on your home. Check that the exact model name on your purifier matches the compatibility line before you add filters to the cart.
Filter-cost worksheet (fill in your own numbers)
| Blank | Your number | Example using the Levoit 2-pack page above |
|---|---|---|
| A. Pack price | $____ | $54.99 (regular price shown Oct 2, 2026) |
| B. Filters per pack | ____ | 2 |
| C. Price per filter (A ÷ B) | $____ | $27.50 (rounded) |
| D. Months you assume between changes | ____ | 6 to 8 (maker’s recommended range) |
| E. Filters per year (12 ÷ D) | ____ | 2 at 6 months; 1.5 at 8 months |
| F. Yearly filter cost before tax/shipping (C × E) | $____ | about $55 at 6 months; about $41 at 8 months (a yearly average — filters come in 2-packs) |
Rows C, E and F are our arithmetic on the page’s figures, not prices Levoit quotes. Your real number changes with how often you actually replace the filter, your tax and shipping, and the price on the day you buy.
Checklist before you pay
- Length × width of the space I’ll use it in: ____ sq ft. Open plan or high ceiling? ____
- The CADR (particles) on the label is at least what EPA’s chart suggests for that area.
- If the box gives an "up to" room size, I found the ACH or CADR that goes with it.
- I know the noise rating and which fan speed it applies to — or I’ve noted it isn’t published.
- Filter: exact compatible model ____, filters per pack ____, recommended interval ____, my yearly cost ____.
- Gases (including many odors) are a separate question: EPA says the CADR rating system is for particles only.
One more line from EPA worth keeping: EPA does not certify or recommend specific brands or models of air filters or portable air cleaners.
Sources (read October 2, 2026, 18:28 KST):
- US EPA, "Guide to Air Cleaners in the Home" — https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home
- Levoit US, "Core 300-P Replacement Filter 2-Pack" — https://levoit.com/collections/core-air-purifier/products/core-300-replacement-filter-2-pack