Methodology: your questions about our sauna ratings

Where do the numbers on a sauna card come from?

From the exact Amazon listing that card describes, and from nowhere else. We read the listing title and feature bullets for four things: a stated person capacity, a named panel type, low-EMF wording and a named cabin wood. Each match is stored with the phrase it came from and a note of where it was read, so any figure on this site can be traced back to a line of seller text.

Those four attributes feed a formula. Nothing is inferred from a similar model, a competing listing, a review or a manufacturer website that describes a different configuration. A cabin that states none of the four is not guessed at — it is scored on how completely the listing is documented instead, and the methodology identifies the component used before the review blend.

What exactly are the two formulas?

Documented spec fit = 100 × [0.40 × min(stated person capacity / 4, 1) + 0.25 × spectrum score + 0.20 × (a low-EMF claim appears in the listing ? 1 : 0) + 0.15 × (a cabin wood is named ? 1 : 0)], rounded to a whole number. The spectrum score is 1 for a full-spectrum listing, 0.75 for a far-infrared listing and 0 when the listing names no panel type. Person capacity must be stated in the exact Amazon listing text with the word “person”; the low-EMF term is recorded as a manufacturer claim copied from the listing, never as an emission measurement of ours. This index summarizes how completely a listing documents cabin size, panel type, EMF wording and material — it is not a comfort test, a temperature measurement, a safety judgment and never a statement about any effect on the body.

Documentation completeness = 100 × [0.5 × min(feature bullets / 8, 1) + 0.3 × min(listing images / 5, 1) + 0.2 × (brand stated ? 1 : 0)], rounded to a whole number, computed from the stored Amazon listing record when the listing text never states a person capacity. It measures how completely a seller documents a listing — nothing about how the cabin performs or feels.

The split matters more than either formula. A stated capacity selects the spec-fit component; otherwise the stored listing record supplies the documentation-completeness component. Sanitizing merchant display text does not change those raw inputs.

Why do you trust a listing’s low-EMF claim only as a claim?

Because we have not measured anything. Measuring electromagnetic emissions requires a meter, a repeatable protocol, a fixed measurement distance and physical access to each cabin. We have none of those, and a comparison site that publishes emission rankings without them is inventing numbers.

So the low-EMF term in our formula records one fact: the seller addressed the subject in writing. That is worth a fifth of the spec-fit score because a listing that names its EMF position is better documented than one that ignores it — and it is worth nothing more than that. Our low-EMF comparison repeats the same caveat on the page itself.

How do Amazon reviews enter the rating?

Where Amazon publicly displays customer reviews for a listing (average star rating and review count captured from the public product page), the raw editorial score is 100 × [0.45 × (Amazon average / 5) × min(review count / 50, 1) + 0.35 × min(log10(1 + review count) / log10(1 + 5000), 1) + 0.20 × documentation score / 100]. The confidence factor min(review count / 50, 1) damps averages based on very few reviews, and the logarithmic volume term rewards large public review volumes, so widely and highly reviewed listings rank ahead of thinly reviewed ones. Listings with no captured public review data use the documentation score alone. This combined index reflects the public Amazon reputation and the listing documentation — it is not a physical trial, and we have not used the products ourselves.

The confidence factor reduces the contribution of averages based on fewer than fifty reviews; the volume term grows logarithmically. Comparators include only complete sauna listings with a captured Amazon average and positive review count for the exact ASIN, plus the stated capacity, construction or listing-claim criterion. Listings without collected review evidence remain in the catalog, but not in ranked shortlists. Amazon may group reviews across variations; the stored count is what its exact-ASIN page displayed, not proof that every review concerns only that configuration.

What does 8.7 out of 10 actually mean here?

It is our overall rating for that sauna, on a 0 to 10 scale with one decimal. Most of it comes from the evidence above: what buyers say about the exact listing, how many of them have said it, and the specs and warranty the seller actually puts in writing. The rest is our editors' judgement of how the saunas in a ranking compare with each other.

An 8.7 does not mean the sauna is better built, more comfortable or safer than an 8.1. We have not sat in these cabins or measured them, and the number is not an Amazon customer rating. Rankings run from the highest rating down; when two saunas tie exactly, the listing slug decides, and that is a stable identifier, not a quality signal.

What never appears on this site?

No claim about any effect of infrared on the body, in any phrasing, anywhere in our own copy. No installation guidance: we report the voltage a listing states and refer every question past a standard household outlet to a licensed electrician. No prices or stock levels: every button opens the exact Amazon listing, where the current offer applies. Review counts and editorial scores are built from the stored evidence snapshot and do not update until a rebuild. No physical test results, because we have run none.

How do I report something wrong?

Write to [email protected] with the page URL, the listing identifier and the statement concerned. Because every extracted attribute stores its source phrase, a correction about a capacity, a wood or a voltage is usually verified in minutes. The affiliate disclosure covers the commercial relationship, and the editorial charter states the principles these formulas implement.

Spec-based ratings

Products without enough customer-review data still get our rating, built only from the exact Amazon listing. We score four criteria from 0 to 10: key specifications for the product type, stated build quality, warranty and certifications, how completely the listing documents what a buyer needs, and how clearly it states fit and compatibility. The rating runs from 4.5 to 8.5: 4.5 + the average of the four × 0.4. A thin listing lowers the rating but never below 4.5, because a short listing is not proof of a poor product; the 8.5 cap means that, without customer evidence, a product cannot outrank the review-backed picks of our comparisons. These are editorial judgments from documented facts, not from our own use, and they are labelled "Spec-based" wherever they appear.