Stiina, my broth on the stove reduces by about half in 12 hours and I get about 2 quarts yield. In the crockpot, there was literally about a cup left after 24 hours.
I've totally been wanting to try perpetual bone broth too, Michelle, thanks for reminding me of that!! That sounds like something that really needs the crockpot (having my stove on for days at a time doesn't sound like such a great thing right now!) so I'll have to get that figured out first.
The tin foil under the lid could be a great idea Stiina, update us on how it goes!