Does anyone see a problem putting a hub in a non climate controlled metal barn in northern IL where summer barn temps reach about 110F and winter temps can be -5F? It would be protected from snow and rain, but should I consider protecting it from condensation and humidity by putting it in a weatherproof box?
Anyone have one in an outbuilding or shed?
I wouldn't be too worried about the cold, other than possible condensation. I'm not sure a weatherproof box would really help with that, but since the device is passively cooled, that might make the heat problem worse in the summer--and at that temperature range, heat might be more of a concern. Here is a thread where you can find some speculation on this topic:
That being said, the hub doesn't have designated operating temperature, so most of these are just best-guess guidance based on similar electronics. You won't necessarily for-sure fail in either scenario. Depending on how close the barn is, you might be able to make the traditional Zigbee or Z-Wave mesh work with devices in that location (presumably you also have a hub in your home?), but at longer distances, that becomes less practical.
Here are some other threads you can find on temperature in case you are curious, though again most is just general commentary since there are no guaranteed specs for this:
Commercial IC are rated 0°C to 70°C. Beyond that there is a likely wide safety margin. I don't know what is in the Hubs.
I would say most of the Commercial IC's are either similar to the "industrial" IC spec of -40 to +85 °C with shortfall at the high temperatures.
The real culprit causing failures is fast thermal changes. I expect you won't have any real fast temperature swings.
The rest is circuit design.
I think it is worth a shot at your temps.
The best protection would be for dust and dirt with no seal to contain any moisture. Should have open airflow.
You can also use @thebearmay's excellent "hub info" device driver to collect and monitor various hub stats. That'll at least give you visibility to what the internal operating temperature is.
I say try it, and report back periodically. Just make backups so as to not require a complete do-over should it fail. My guess is that you'll be fine, but no-one is sure, it seems. I keep one of my hubs in a heated but not cooled garage, but we're in Maine so we don't get your heat (yet, anyway).
Thanks for the responses. I will be ordering one to try. I wish the barn was closer, but its just too far away for anything to pair with my house hub. Even tried a couple ring 700 series extenders out in the shed, with 700 series mains devices in the barn. The metal constuction of the barn and the distance is just too much.
I do not know where you live in Northern IL, but I live just south of the McHenry County line, one of the northernmost counties in Illinois. A few years ago, during a polar vortex, the temperature dropped down to -27 F here and Rockford recorded a record low temperature of -31 degrees. Chicago was a balmy -23 F. I know those deep freeze temperatures are uncommon, but they can occur.
It is best to make preparations for such extremes. For example, in the event of extreme cold, you might keep a few iron-air based hand warmers available to elevate the temperature slightly during the coldest nights. Or keep a portable space heater nearby. Of course, be sure all safety precautions are followed.
Also for summer when temperatures go above 100 degrees, you might employ a small fan to blow air across the top of the hub. The moving air will help the hub release heat. A 5-6" fan powered by battery, USB, or AC should be sufficient.
Which could of course be connected to a Zigbee/Z-Wave switch and turn on automatically when temps hit x degrees for y minutes or more. 
I'm mostly worried about the cows, who I have heard think they are good w/home automation, but usually just end up having to call in the pigs to fix what they've messed up.
I wish we had some pigs** to fix our Congress
Pigs as in farm animals, the ones @danabw has to fix his automations after the cows messed them up.
Great idea about the fan, and also great idea about automating it. I can't wait to get some zwave out there.
Shhhhh don't tell anybody cause I've yet to sign up for Hub Protect.
C-5 in dusty metal out building,
so far seen 115F(often) down to 10F(occasionally),
humidity nothing like what you experience ...except when it rains or snows,
but I can top your dust any day.
Do I like the setup, no...it goes against every notion of proper equipment environment in my archaic "chill-yah-to-the-bone-computer-room" past.
But, I really couldn't amend this much...and quite frankly, when I put it in there was so much else that was a functional concern that I just drove on with it as "a test". It's still in "test mode" I guess.. 
Over time I worry about the heat the most, but things are still working now in the 2nd Winter and heading into 3rd Summer.
That fan idea is good, but I worried about making the dust load that gets into the C5 even worse.
Mesh Tip just for you: I put an IKEA Trådfri (ZigBee) Signal Repeater in a small plastic Telco box on the outside of the metal building, strung a 15? foot USB cable from it to the power plug that comes with it and plugged it into a small APC UPS which the hub is also plugged into (that is probably a good thing for giving the hub some love even though I'm beating it up environmentally).
Download the Hubitat app
