For about six weeks now I have been using my old Rival 6 qt (7 qt.?) crock pot to humidify my combination sleeping and living area. It works GREAT. When I get up I add about three quarts of hot tap water, 2 qts. or so mid-day and about three just before I go to bed. I just put hot tap water into a sauce pan, bring it into the room where the crock pot is and pour the water in to up close to the top where it would then hold a cover. [I certainly don't measure the amounts, just list them here to give you a clue approximately what amounts of moisture I am adding to the air. And how much work it is to keep filled. Answer: not much. If I'm experiencing days when my wrists are weaker I just make a few more trips with less water.] Of course I don't use a cover!
I have the setting as "high". Without a cover it doesn't actually simmer the way it would even on the low setting if the cover were on. It just nicely evaporates/ gently releases steam. I do have the area under it protected but haven't spilled anything yet. This is the best winter sleeping I've had in years. I still have insomnia but, not infrequently now, I'll come up with 5 or 6 or a rare 7 hours...I can hardly believe it. Now I don't have to get up in the middle of the night to put pots of water on the stove.
We have very hard water. I use a teaspoon or two of baking soda---once---in the bottom of the crock pot before I fill it for the first time each week. That's after I've cooled the crock a bit, dumped the water, and soaked/swished it with quarter strength vinegar for about 20 minutes. [That is, a half cup vinegar to 1-1/2 cups water would work.] Sometimes I use a plastic scrub pad on the sides a bit. That's IT for the cleaning and disinfecting process!
[I had a more than disappointing experience with an ultrasonic humidifier---will post that in another thread.]