My S9 is a September batch, and I don't think they like to run warm. Or they still like to run warm?
Highly unlikely that they like to run warm. That is why they have specs that allow them to run as low as 0°C, but want to be run at no more than 40°C. Computer processors and similar chips, such as CPU's, GPU's and Antminer's ASIC chips, run better when it's cooler. The fans run in proportion to the heat inside the miner. So, you will, at least, be paying less in electricity with the lower fan speeds. And, my thought is that power usage should be lower if the chips aren't having to work as hard in higher temperatures.
It would be interesting to see if miner users have charted power usage in relation to operating temperature.
The trick is to keep the Antminer within specs. And, 0°C is the floor for Operating Temperature. I am considering the installation of electrical outlets in my garage so I can run my L3+, and my upcoming S9, in the garage during the winter.
My garage's temperatures are not likely to fall below 0°C. And, I will have to find somewhere else for them when winter is over. But, you still have to be careful of moisture and dust. My miners would be near the far wall, away from the garage door.
I think most miners understand, but if you are new to running these machines, the area where you have your miners should be clean and free of dust, and not be in an area where dust could be coming in. You also need good air flow, which I think most miners understand.
Otherwise, reading Bitmain's specs is important. Bitmain very likely has good reasons for specifying the specs that they do.