I live in a 680 sq ft concrete construction high-rise rental apartment in Redwood City, CA, with electric heat only, and I have a problem with dry air in the (fortunately short) heating season. I have to run my drug store vaporizer nearly 24/7 just to keep humidity over 30%. I go through several gallons of water a day, and my sinuses really don't like it when humidity goes much below 30%. This is crazy. Where is all that moisture going?
I'm pretty sure I'm losing humidity by air exchange, not condensation. It's just not that cold outside. I've looked around for obvious leaks. The walls, floor, and ceiling are concrete, and the windows, while enormous, aluminum framed, and single pane, do at least seem to be decently sealed.
My chief suspect now is the bathroom vent. It's just a register connected to ductwork with a central fan somewhere. It's always on and it seems to be sucking mighty hard. I'm thinking that if it's the culprit, I can just cover the register and take the cover off when I shower. So how would I go about measuring how much air it's sucking out of my apartment? Without expensive equipment?