james wrote:
I'm using a $20 household fan 24/7 to ventilate a damp crawl space by
sealing it against one of the crawl space vent (i.e. becomes an
exhaust fan).

Eventually this fan is going to fail, perhaps the bearings wear out
and then the fan stop spinning.

Should I worry about a fire, or do all UL listed fan have some sort of
overheat protection?

Is there some sort of fan that is designed to run 24/7 and is well
protected against overheating?

It probably depends on the fan. Some of the newer ones I've taken apart
have a thermal fuse in line with the run windings. If the fan stops for a
sufficient enough period of time, the solder inside of them vaporizes off,
and the fan no longer functions.

Jon