Asidius Aluminium Sauna Thermometer and Hygrometer Review

The most important decision in this product is the material, and it has nothing to do with accuracy. A sauna is a hot room containing barefoot people, wet wooden benches and no shoes, and a glass gauge that falls off a wall in there is a genuine injury risk.

Asidius builds this in aluminium specifically to remove that. The listing states it survives a drop and frames it as no longer worrying about the risk of glass breakage, which is the right priority for the environment rather than a durability boast.

Combining the thermometer and hygrometer is the second sensible decision. Sauna conditions are a combination of heat and humidity rather than either alone, and the same room at the same temperature feels completely different wet or dry.

The stated ranges fit the application. Temperature from 40 to 240 degrees Fahrenheit spans a cold room through to a hot traditional sauna, and humidity across the full scale covers both a dry Finnish-style session and the spike after water goes on the stones.

The coating is described as military grade, waterproof, anti-corrosion and high-temperature resistant. Ignore the grade language and note what it has to do: a sauna cycles from cold and dry to hot and saturated repeatedly, and that cycling is harder on a finish than constant heat would be.

Corrosion resistance matters more than it sounds for the same reason. Condensation forms on every surface as a sauna cools, so a gauge body spends part of every day wet, and an aluminium part with a poor coating would pit and stain within a season.

Mounting is a single screw, which Asidius says takes seconds and includes in the box. On a sauna wall that is the right approach: fewer holes in a tongue-and-groove cedar or hemlock lining is better, and a single fixing lets the gauge be moved easily if the first position reads oddly.

The red pointer is a well-judged detail. Asidius notes it is easier to read in a room full of water vapour, and that is true: contrast is what carries through steam, and a thin dark needle on a dark dial is hard to pick out when the air is misty.

Glass-free construction also has an effect on response. Without a glass front the sensing elements sit closer to the air, which Asidius claims makes it more sensitive, and a gauge that lags badly behind the room is of limited use when you are deciding whether to add water.

The accuracy claim is where the listing overreaches and it is worth being direct about. Asidius calls it laboratory level precision and then states the figures: a minimum reading of 10 degrees and an error of no more than 5 degrees Fahrenheit.

Those two figures describe a coarse instrument, not a precise one. A 10 degree scale interval means you are estimating between graduations, and a tolerance of 5 degrees is half of one interval. That is entirely adequate for a sauna and nothing like laboratory precision.

Judge it for what sauna use actually requires, which is knowing roughly how hot the room is and whether it is still climbing. Nobody needs a sauna temperature to a degree, and a clear needle you can read through steam is worth more than resolution you cannot use.

Asidius is then unusually honest about two things the claim glosses over. The listing says to calibrate using the rear adjustment before use, and that position within the room affects readings even within the same sauna.

Both of those are true and most listings never say so. Heat stratifies strongly in a sauna, so a gauge near the ceiling reads far higher than one at bench level, and the figure you get depends as much on where you mounted it as on the instrument itself.

Mechanical hygrometers deserve the same caution. They are approximate at the extremes of their range by nature, so treat the humidity needle as showing a direction of travel rather than a percentage you could record.