What is the best temperature to run an S19jPro at?
Hey jason - Great question!
Most ASIC machines like something in the 83F - 86F (28C-30C) for their intake (cold) side but you can be below or above that within a reasonable range.
You just want to avoid sustained intake air over 100F, especially if your exhaust isn't damn near perfectly balanced. At that point you may need to shut some (or all) of your miners down during the hottest part of the day. It is a bummer, I know, but it's only temporary and MUCH cheaper than the AC system you would need to cool things off on the intake side.
The key to keeping your intake temperatures in a reasonable range is to manage your exhaust and any related back-flow of exhaust air. That positive feed-back loop can be a killer.
Calculate how much air flow the machine (s) will be pushing - for instance, the Antminer S19's push roughly 400-450CFM per machine meaning that for every S19 you are operating you need to bring in that much free air flow (plus maybe an extra 20-25%) and have an exhaust fan (s) pushing out the exhaust air flow without pulling from the miners. In other words, don't try to exhaust more than your air flow allows! If you do, you will drive your miner (s) into fault and potentially have big problems.
A good rule of thumb is that if your mining room door is sucking shut you have too much exhaust and not enough free air flow.
Balanced air flow & venting is probably the most important part of operating your mines efficiently and keeping those fans rocking for three or four years instead of only two.