My building is essentially a single extremely large room. It's a 25'W x 45'L x 20' H concrete box, with an open mezzanine over the back 1/3 of the box. The HVAC system is gas-fired forced air, installed outside on the roof, and due to the foolishness of the builder, the heating registers are all at the ceiling level, except for one under the mezzanine. The air return is in the middle of the ceiling. The only water is also under the mezzanine.
EDIT: There are basically just two runs of ductwork. One comes from the roof-mounted HVAC unit, and runs down one side of the ceiling. I'd guesstimate it at 8" x 12" ish, and it has four registers along it. There's a single branch off the ceiling duct that comes down and runs along the underside of the mezzanine - flexible and maybe 8" diameter.
I've been looking to get a humidifier, and all the stand-alone units of a size that make sense for a space this size get pretty mixed reviews (and also require filling multiple times a day). Installing a whole-house humidifier at the furnace is not an option, due to its location.
My question is: can a whole house humidifier be installed somewhere other than at the furnace? My options: (expensive) run water up to the 20' ceiling and install on a duct up there. (easier) install on the one duct that's near water, under the mezzanine - but that's only about 25% of the incoming air.