I have a model 21 hatcher and a model 50 drum incubator that I am in the process of getting going...making room for the drum to be set up and have parts on order for the hatcher.
I would try to get your Humidaire set up and running as soon as is prudent so that you can troubleshoot it...mine wouldn't stabilize so I have new switches and wafers on order for it, since those have never been changed. There is a guy up in Minnesota that deals these parts at Sunny Creek Farms, don't have his number handy just now, but best to get it going and make sure everything is status quo before you go getting eggs lined up for it. I had to pull mine back out of the hatcher when I realized the temperature couldn't stabilize on its own after I set those eggs. You would be well advised to order the manual for this machine if yours didn't come with it and a set of backup wafers, just in case...especially important if yours was stored in a cold storage shed like mine was. And I would double-check your thermometer on it too, because mine is off-kilter...checked it against a
Brinsea Spot Check, which is supposed to be one of the best. I am not worrying about that thermometer right now though because I have several others at hand. The Spot Check is a great tool though and I honestly feel a serious hobbyist hatching eggs should not be without one...my first hatch yesterday of 6 eggs was at 100% success, so there's the proof in the pudding. If yours has only ever been in a house, you might only have to turn it on, add distilled water, and fine tune the temp.
I don't want anyone new to this discussion to get the notion that these machines are troublesome, they do in fact have a great reputation and I have had a lot of old timers recommend them...my two have been used very little and have been sitting in a shed most of their lives, so it stands to reason that we're going to have to adjust them. They're in fantastic shape but the stickers on them tell the operator not to store them under 40 F, and unfortunately that happened.