In the summer in Florida, with normal ground water (which is usually pretty tepid, because, Florida) my cubes only take like 4 minutes to soak/mash up. Winter water is colder, but I still don’t NEED to use heated water, it only takes like 10 minutes. I do have a water heater, just need to fix a pipe, and I can’t imagine using actual hot water would take any more than a couple minutes to mash up.
You have electric at your barn, can you put in a water heater and just soak them right before feeding times?
When I lived in Ohio, to prevent water buckets and troughs from freezing several barn owners just insulated them, didn’t use heaters, perhaps that would be a solution for you. Water buckets we’d wrap styrofoam around, then layer on the duct tape. Water troughs would build a wood insulation box for, you could build something like that for your feed bin.
Or a big cooler or freezer to store them in?
https://www.dacocorp.com/containers-…ar-ice-totes#1
I would not be comfortable running a space heater overnight. My parents’ neighbor’s barn burned down from exactly that just a couple of years ago.