Plastic can get very brittle and shatter in cold. Have you ever tried to use a vinyl extension cord at -20?
Monitor the condensation on the outside of your tubes carefully, especially in the summertime. You don't want the innards of the computer to get moist. Excess humidity may not be a problem for you in the dryness of winter, seeing as how you already use a drum type humidifier to try and compensate.
If your cooling system is split between elevations (upstairs/downstairs) keep in mind that the coolant pressure in the system will be higher at the lower elevation-downstairs. If the coolant has the specific gravity of water, a 10 foot change in elevation will cause the liquid pressure at the lower point of the system to be about 5 psi.
Add a coolant reservoir at the highest point. Centrifugal coolant pumps generally have a hard time if any air in pipes accumulates at the top.
Did you discover that guck in your humidifier while investigating the possibility of running the hoses through the air ducts? Man, throw that humidifier away. I bought one just like that when I lived in Winnipeg. We were getting sick quite often until I discovered that bacteria and mould infested gelatinous slime in the humidifier.
Looks like your stove was recently raised. I did the same thing too, with the 4 inch board nailed at the bottom. It was too low to be kid proof. And that Jana box? I haven't seen the Jana brand for years. I thought they were out of business.
EDIT: Oh, I just remembered - in case of leaks, Propylene gycol is not toxic. Ethylene glycol tastes sweet but is poisonous to pets. Major liver damage.
Regards, Bob