Just for clarification, you mean "DE-humidifier" or "humidifier", because I've got some answers for both..
I am gonna watch the video in a second, but learned a bit about vapor pressures back in my college days, and it truly does make a difference when growing.. During the spring/summer, my plants seem to be a little more full and the leaves a little more resilient.. During the winters, it's a struggle to keep RH up, but I use a high-volume humidifier, placed on the opposite side of my scrubbers, so the scrubbers pull the moisture across the room, same w/ my CO2 bags.. The humidifier I have would fit in most places and has a tank that is roughly 1.5gals.. For me, on a medium setting, it lasts about a day or so, so even if it doesn't need it, I'll top it off in the morning when I'm down checking out everything.. I've seen a lot of the small, "cool-mist" generators and they work, but the refill rate is ridiculous!!
The inverse is true for the Summers though.. I have to run my large-scale dehumidifier to maintain 55% RH for my basement, as there are some drawbacks to running dehumidifiers.. First off, they are just like running an AC; lots of power draw, even from the "Energy-efficient" models.. I am still emptying the 1.3gal tank AT LEAST once a day, which means this thing is cycling on and off, ALL day.. Sorta hurts the energy bill, but without it, my basement sits at a balmy 80%-ish RH, so no good for flowering..
An idea I had, that worked kinda well, but required some equipment that not everyone has, is to basically set-up a small plastic tote w/ an air pump and a couple airstones in there.. Fill it with water, and run the airstones full speed.. The bubbling and churning of the water will moisten the air a bit, as I had a similar issue when I did hydro and my res. wasn't always sealed tightly and I had several airstones in there.. Definitely worth a shot if you already have the gear around, and it's cheaper than buying a humidifier..
During the Winters, I try to keep my grow in the 40% range, and they do well.. Some strains/phenos responded differently, but for the most part, I'd see a little canoeing of the leaves, sometimes spotting or unusual leaf growth.. If they were still not quite in full flower, I'd mist them every morning to see if it helped, and sometimes it did..
