Methodology
How We Rank
The most important page on this site. It is what stands in for the testing lab we do not have.
By Scooter M. · Published · Last updated
The short answer
We compile published manufacturer specifications, check coverage claims against AHAM’s room-sizing rule, compute what each unit costs to run for a year at the current US average electricity price, and publish the arithmetic so you can redo it. We rank on that. We have not tested any of these units.
What we do not do
We are putting this near the top rather than burying it, because it is the thing you most need to know before trusting anything else here.
We have not tested these units. We do not own them, we do not have a lab, and we are not going to tell you we do. Everyone in this category will tell you they tested twenty air purifiers. We have not tested any, and we say so.
We also do not accept free products, we do not sell placement in any ranking, and we do not have a panel of experts. There is one person writing this site.
That is an unusual thing to lead with on a page that exists to make you trust our rankings. We do it because the alternative - a testing claim with no published protocol, no equipment list, no photographs and no raw data - is what several sites currently outranking us offer, and it is trivially falsifiable. We would rather be checkable than impressive.
What we do instead
- Compile published specifications. Every figure on this site is attributed to whoever published it, in the spec table on the product itself. Where a manufacturer does not publish something - a filter replacement interval, a CADR - we write that we could not find it rather than estimating.
- Check coverage claims against AHAM’s rule. Coverage figures are the most misleading number in this category, because they depend entirely on an assumed air-change rate that is rarely stated. We size against the rule instead.
- Compute annual running cost. Nobody publishes this and it frequently exceeds the price difference between two units over three years. The formula is below and the working is on every product.
- Read owner reports at volume for failure patterns. Reported as owner reports, attributed as such, and never presented as our own experience.
- Publish the negative case. Every product carries a “who should skip this” and every commercial page carries a “when to buy nothing at all”. If a page can be honestly written to talk you out of the purchase, we write it that way.
How we rank, in order of weight
| Criterion | Weight | What it means |
|---|---|---|
| Fit for the stated job | Highest | A unit that is the wrong size or the wrong mechanism for the page's use case cannot rank, whatever else it does well. |
| Published specification transparency | High | Manufacturers who publish coverage at a real air-change rate, or power draw per fan speed, rank above those who publish one flattering number. |
| Computed running cost | High | Cost to own for three years, not price on the shelf. |
| Honesty of the coverage claim | Medium | A 1,718 sq ft headline against a 358 sq ft useful figure is a mark against the unit, not for it. |
| Practical constraints | Medium | Noise at the speed you would actually run it, tank size against how often you would empty it, whether the pre-filter is washable. |
| Failure patterns in owner reports | Tie-breaker | Recurring, specific reports of the same fault. Attributed as owner reports. |
Ties are broken on running cost, because that is the difference the reader keeps paying after the purchase is forgotten.
The arithmetic, in full
Everything below is reproducible. If you disagree with a number on this site, you should be able to find out why without asking us.
Annual electricity cost
(rated watts / 1000) x hours per day x 365 x electricity rate
We use 18.34 cents/kWh, the US average residential price of electricity. Source: U.S. Energy Information Administration, Electric Power Monthly Table 5.6.A (June 2026).
Worked example. The Levoit Core 400S is published at 38 W. At 12 hours a day: 38 / 1000 x 12 x 365 = 166.4 kWh. At $0.1834 per kWh that is $30.52 a year. Compare the Winix 5500-2 at a published 70 W: 70 / 1000 x 12 x 365 = 306.6 kWh = $56.23 a year. Over three years, a $77 difference - frequently more than the gap in purchase price.
Where a manufacturer publishes power per fan speed, we use that instead of the single rated figure, because it is far more informative. Coway publishes 3.7 W on speed one and 75.3 W on speed three for the same unit: $5.94 a year against $120.97 at 24/7 running. That twentyfold spread is exactly the kind of thing a single rated wattage hides.
Air purifier room sizing
required smoke CADR = room area in sq ft x 2/3
This is AHAM’s published guidance: “choose an air cleaner with a smoke CADR rating that is two-thirds the size of the room’s area,” with their own worked example that “a room that is 200 square feet would require an air cleaner with a smoke CADR of at least 132.”
Two adjustments. For ceilings above eight feet, multiply by 1.125 (9 ft), 1.25 (10 ft) or 1.5 (vaulted) - CADR is about volume, and area only stands in for volume at a fixed height. And for wildfire smoke, AHAM recommends a smoke CADR equal to the room’s square footage rather than two-thirds of it.
Dehumidifier sizing
From published manufacturer sizing conventions, which classify a space by how wet it is rather than by area alone. Roughly 20-22 pints per 500 sq ft for a merely damp space, stepping up a size for each level of wetness. The full table is at what size dehumidifier do I need.
Humidity targets
The EPA states that indoor relative humidity should be kept below 60 percent, ideally between 30 and 50 percent, and that wet materials must be dried within 24 to 48 hours to avoid mold growth. Every humidity recommendation on this site traces to that guidance.
The score
Each product carries a visible score out of 10, built from four to six metrics chosen for the category - clean air per watt, honest coverage claim, refill interval, cold-room performance, and so on. The metric scores are shown on every product so you can see what produced the total.
Where our numbers come from
| Source | Good for | Where it is weak |
|---|---|---|
| Manufacturer specification pages and manuals | CADR, wattage, tank capacity, pint rating, dimensions, noise | Coverage claims, which are chosen to flatter. Filter intervals are frequently absent. |
| AHAM and AHAM Verifide | The AC-1 test standard, verified CADR figures, room sizing | Not every model is submitted for verification. |
| EPA indoor air guidance | Humidity ranges, mold and moisture, biological contaminants | Deliberately general - it will not tell you about a specific product. |
| US Energy Information Administration | The electricity price behind every running-cost figure | A national average. Your local rate may differ substantially. |
| Live retailer price data | Current price and availability | Changes constantly, which is why we date-stamp it and hide it when stale. |
| Owner reports at volume | Recurring failure patterns | Self-selecting and unverifiable. We use it as a tie-breaker, never as a spec. |
Prices
Prices render only from a live data layer, and they carry the date they were checked. If that data is more than 48 hours old, the price disappears and the button says “Check price on Amazon” instead. We would rather show you nothing than a number that has moved.
We never write a price into the text of a page. Every price you see on this site came from the data layer at build time, or it is not there.
How we make money
Affiliate commission. When you buy through one of our links we earn a percentage at no additional cost to you. We are a participant in the Amazon Associates Program, and every buy link on this site currently goes to Amazon.
It does not affect rank order. The commission rate is effectively identical across the products we compare, so there is no commercial reason to prefer one over another - and where a page’s honest conclusion is “buy nothing”, we write that, which is the clearest evidence we can offer that the ranking is not for sale. Full detail at our affiliate disclosure.
What would change a ranking
- A specification correction. If a manufacturer publishes a revised figure, or we have transcribed one wrongly, the number changes and the ranking follows it.
- A discontinued model. Removed or replaced within the quarter. A roundup with dead links is worse than no roundup.
- A price shift that changes the cost-to-run conclusion. If a unit’s filters double in price, its three-year cost changes and so does its position.
- A failure pattern emerging in owner reports. Consistent, specific, recurring - not a handful of one-star reviews.
- New guidance from the EPA or AHAM. Every page citing it gets updated.
How to tell us we are wrong
Email info@mistandmeter.com with the page and the figure you think is incorrect. If you are right, we correct it within seven days and mark the correction visibly on the page. Our full correction policy is at editorial policy.
This is not a formality. The entire argument of this page is that our numbers are checkable - which is worth nothing unless we act when somebody checks them.
Sources
- AHAM - Tips for Choosing the Ideal Portable Room Air Cleaner
- AHAM Verifide - Air Filtration Standards (AC-1)
- EPA - Mold Course Chapter 2: Why and Where Mold Grows
- EPA - Biological Pollutants' Impact on Indoor Air Quality
- U.S. Energy Information Administration, Electric Power Monthly Table 5.6.A (June 2026)