Maybe I am using the wrong terminology. I mean those oil-filled mini-radiators.
Like this.
View attachment 4027638
I think those are pretty safe.
A plan is forming in my mind. A day-time warming station using a small oil filled radiator under the overhang of the hospital bay which will trap the heat and they can cuddle up there if they choose to.
Then I am going to hang a couple of big umbrellas (need to see what I have) from the rafters to trap the heat lower down and hopefully just above the roosts to keep them cozy at night.
Slight issue is that they have taken to roosting randomly all over the place but hopefully they will have the sense to roost in a warm spot when it is that cold, but no accounting for chickens!