Sauna · Water · Air

The technical questions that block a home systems purchase

Somebody about to spend five thousand dollars on a sauna needs to know what breaker it takes. Somebody comparing air purifiers needs to know what “covers 1,500 sq ft” is actually claiming. Those questions have published answers, and almost nobody puts them in one place.

4 ×What identical sauna use costs in Hawaii versus Nevada. Not a property of the heater.

1.0 ACHWhat a 200 cfm purifier sold as covering 1,500 sq ft is really promising.

30 vs 35 AThe breaker for a 6 kW heater: manufacturer manual against the code formula.

58.6 vs 75Gallons per person per day. Metered research against the sizing convention.

Disclosure. This page contains affiliate links; we may earn a commission on qualifying purchases at no cost to you. As an Amazon Associate I earn from qualifying purchases. Every figure on this site is reproduced from a published manufacturer manual, standard or government document and linked so you can check it yourself. We do not own or test the products we write about, and we say so on every page rather than implying otherwise.

What we do differently

We do not review products, because we do not own them and we are not going to pretend otherwise. We reproduce what the manufacturer manuals, the standards and the federal guidance actually say, link every source, and show the arithmetic in the open. Where two published sources disagree, we show both and say so — because that disagreement is usually the thing you needed to know.

Start with a calculator

Sauna heater sizerkW from Harvia's published rule, then the breaker and wire the manuals specify next to what the code formula gives. Water softener and filter sizerGrain capacity as a range, peak flow in GPM, and the NSF certifications to demand in writing. Air purifier CADR sizerTurns the coverage area printed on a box into air changes per hour. Running cost by stateWhat a sauna, an air purifier and a softener cost to keep running where you live, and in all fifty-one states.

By subject

SaunasVoltage, room sizing and what a plug-in cabin can and cannot do. Water treatmentSoftener sizing, hardness, certifications and what your utility already owes you. Air purificationCADR, air changes and the difference between a coverage claim and a specification. Installation and codeThe cross-cutting electrical and plumbing questions that decide whether any of it can be fitted. All calculatorsEvery calculator here is free, works without an account and can be embedded on your own site.

Four disagreements we found without owning a single product

These are the reason the site exists, and they are all checkable against the sources on each page.

Sauna breakers. Manufacturer manuals and the NEC continuous-load formula give a different breaker at every heater size — 30 A against 35, 40 against 45, 50 against 60.
GFCI on a sauna heater. Harvia's guide says not to use one. NEC 210.8 requires GFCI protection in the locations many saunas sit in.
Water softener sizing. The trade sizes on 75 gallons per person per day. The metered research says 58.6. That is a tank size.
Air purifier coverage. A 200 cfm unit sold as covering 1,500 sq ft is claiming exactly one air change per hour, against the roughly five that EPA's own table implies.