Review sites test saunas in studios. Your sauna lives outdoors in Alabama humidity, under Vermont snow, or in a Phoenix garage — and climate quietly decides whether a purchase thrives for fifteen years or rots in five. Here's what to spec for where you actually live.
The enemy is moisture that never leaves. Untreated softwood exteriors mildew and rot fastest here; ground-contact bases wick water year-round.
Spec for it: thermally modified wood (e.g., thermowood — the heat treatment reduces the wood's ability to absorb moisture) or naturally rot-resistant cedar over untreated spruce/hemlock; a gravel or paver pad with airflow underneath — never bare ground; a real roof (barrel staves alone shed rain but standing humidity attacks end grain); and after-session ventilation — run the heater 10–15 minutes with the door cracked to dry the interior, and leave vents open between sessions. Ask any brand: "What's the exterior finish maintenance schedule in a humid climate?" A confident answer with a stain/oil interval is a good sign; "no maintenance needed!" is marketing.
The enemies are roof load, freeze cycles, and undersized heaters.
Spec for it: ask for the snow-load rating in writing before buying any flat- or barrel-roofed unit (many spec sheets omit it — that omission is your answer); prefer steeper roof profiles or fit the brand's winter roof kit; upsize the heater one step (a 6kW room that's cozy in October is slow at −10°F — the 8–9kW upgrade Redwood offers exists for this); and plan the path, not just the pad — a sauna you can't reach through February snow is a shed. Cold plunges: water left in an unpowered tub freezes and can crack fittings — winter users need either a chiller/heater unit rated for continuous outdoor use or a drain-and-cover discipline.
The surprise: heat is harder on cold plunges than cold is on saunas. A chiller fighting 110°F garage air runs long duty cycles — electricity climbs toward the top of the $40–80/month band and compressor wear accelerates.
Spec for it: shade the chiller or duct it ventilation; an insulated tub and tight lid matter more here than anywhere (roughly halving chiller runtime); consider running plunges at night rates if your utility has time-of-use pricing. Saunas themselves are easy in the desert — but UV is not: dark exterior finishes fade and check fast in full sun, so shade siting or UV-rated finishes earn their keep. Indoor infrared in an uncooled garage is fine for the unit, brutal for you in July — most desert owners end up preferring evening outdoor sessions.
The enemy is corrosion. Salt fog attacks heater elements, fasteners, hinges, and chiller condenser coils. Spec for it: stainless fasteners and hardware (ask what grade — 304 minimum, 316 near open surf), rinse-downs for exterior hardware, and site the unit out of direct onshore wind where possible. Ask the brand whether the heater warranty excludes coastal installs — some do, in the fine print. (Warranty exclusions are red flag #6 in the vetting guide.)
Whatever your climate: the electrical requirement doesn't change, outdoor circuits need GFCI protection and weather-rated conduit (your electrician's department), and the cheapest climate insurance is a $30 cover used every time. Factor climate extras — roof kits, pads, covers, upsized heaters — into the 5-year cost before comparing units, because a $500 climate kit on a $5,300 sauna is a 10% price difference hiding in the accessories page.
This guide describes durability and cost factors, not medical guidance — heat and cold-water immersion carry contraindications; consult your physician. Verified unit data: comparison table · full process: buying guide.