Definition
The ASHRAE Thermal Guidelines, published by ASHRAE Technical Committee 9.9, are the de facto reference for how warm and how humid a computing environment can safely run. They split IT equipment into classes A1 through A4 and define two envelopes for each: a tighter recommended range for best long-term reliability, and a wider allowable range the hardware can tolerate without immediate harm. The recommended temperature band for all classes is 18-27°C (64.4-80.6°F).
The equipment classes
Allowable temperature ranges widen as the class number rises: Class A1 (enterprise servers) allows 15-32°C, A2 (volume servers) 10-35°C, A3 5-40°C, and A4 5-45°C. Humidity is bounded too, typically a dew point window with a maximum around 80% relative humidity for A1/A2 rising to 90% for A4, with electrostatic-discharge controls required when air gets too dry. Higher classes trade a small reliability margin for much greater freedom to use outside air.
Why miners should care
Although the guidelines were written for servers, the same physics governs ASIC mining halls. Designing to the warmer allowable envelope is exactly what makes free cooling and evaporative cooling viable for so many hours of the year, cutting the energy spent on mechanical refrigeration. Bitmain and other vendors publish their own ASIC inlet limits, which often run hotter than enterprise gear, but the ASHRAE framework remains the shared vocabulary facility engineers use.
These envelopes underpin the economics in Air-Side Economizer (Free Cooling) and the efficiency metric Power Usage Effectiveness (PUE).
In Simple Terms
The ASHRAE Thermal Guidelines, published by ASHRAE Technical Committee 9.9, are the de facto reference for how warm and how humid a computing environment can…