I want to add something here, before oyu find out the hard way. I used to work for a cigfar wholesaer in South Florida. The warehouse, like every other habitable structure in the Deep South, as air conditioned, drying the ambient humidity and endangering the product. To compensate, the owners installed a mist type humidification system. Soon, there were calcium deposits all over EVERYTHING; walls, floors, desks, computers, shelves, and of course the product itself. This happened because the unit operated by spraying a fine mist of water at high pressure, which also put everything dissolved in that water into the air.
The way to avoid this- something I told the owner before he ran out and got the 'cheapest' thing he could find- is to use a wick-type evaporative cooler, also known as a swamp cooler. Rather than blasting the water into the air will all of its dissolved solids, it drizzles water down a layer of batting inside the machine. A fan blows air through that batting and the water evaporates into the airstream, and this is important, leaving all of its contents behind.
I've scrounged the local thrift shops for years, and I've picked up several units of a particular model, the Essick Air Products' BFC-2000. I didn't pay more than $25 for any of them. I guess they don't make that particular one anymore, but they do make many others. I suggest something like this, small enough to be portable, and WITHOUT digital controls, so you can put it on an external humdistat control. The digital ones, once shut off won't turn on again by themselves.
These swamp cooler type units do not need outside air- unless you're using it for ventilation and cooling- and are plenty simple to operate. Put a sterilant in it every week or two, and of course you'll need to clean it every once in awhile and replace the batting because that's where the dissolved solids end up. I do not recommend any of the whole house units; the ones that go in the furnace ducting dn't put out enough humidity for our purposes, plus they work best with hot water and hot air. I also wouldn't recommend any of the big square jobs, either window or roof mounted because they tend to flow too much air. Maybe they would be fine as a 'first stage', and then you can add more humidity via another unit.
