After posting I read more about ultrasonic humidifiers. If they can suspend minerals in the air, they should be able to suspend TEG, too. But will the TEG stay in the air or precipitate out?

... Do you have a way to confirm it is not doing this? Perhaps measure the specific gravity of the starting and ending solutions in the humidifier.

If I'm reading this graph webbook.nist.gov/cgi/cbook.cg... correctly, the vapor pressure for TEG at room temperature is negligible. I think there is a chance your humidifier is vaporizing the water and just concentrating the TEG is the reservoir. ...