In fact you know the age of a server depending on the amount of dust on it.
There's a defective A/C unit that sometimes throw some water all around.
There's power cut 2 or 3 times a year, the batteries are old so the servers get their hard reboot.
As far as reliability is concerned, sometimes a disk fail, but that's about it.
Now if you think I'm describing something from the third world, you're wrong. It's in France and I'm not exaggerating about it.
So what I'm saying is that for a homelab, don't fret over cleanliness or optimal conditions.
i have to clean my office setup every often and i use a blower to remove the dust. dust bunnies and all. still, everything works.
you are right, people often talk about hygiene for computers but they are more resilient than we are made to believe.
Computers are amazingly resilient if you don't need them for much more than office work.
Only certain systems are fine with being in the garage. For instance, a Supermicro chassis I put out there began rusting in a few spots after a few months, but my custom system that I built was perfectly fine. I suspect the metals Supermicro uses are treated in some way and then cut, but the edges aren't re-treated, allowing rust to form on all of the edges of the chassis.
I never put spinners out there, only SSDs. My bulk storage lives inside my house.
I have an HP Sandy Bridge Xeon box that lives out there and it's always super quiet, but I don't push it hard either. Raspberry pis are super okay with being outside. I'd say if you can make a small Pi cluster, it's a good fit.
I use an open air rack next to my water heater. I don't do any woodworking or anything, so the dust isn't too bad.
The ambient temperature is 32-35°C
The temperature of the disks is 38°C (ssd) to 49°C (hdd), the CPU cores are 27 to 34°C (not sure why there is a difference, it is one CPU).
When I put the computer and other equipment there, I was concerned that the temperature would be unbearable. I am positively surprised.