Hens sleeping in the nesting box. Cold?

[more_old_dogs]

My hens are starting to sleep in the nesting box. Are they cold because their ventilation is too low? There’s a freeze tonight. Roost is open from below and ventilation is upper right. The beige plate heater is unplugged.

 

[cavemanrich]

If chickens are sitting on roost, and they feel a draft from the vent, then maybe they are somewhat uncomfortable. Can you lower the roost bar,at least temporarily, and see if that encourages them to use roost.? I don't see the nesting boxes in pix, but are they much lower than the roost bar??
How many chickens do you have? and are they all crowding into the nest-boxes?

Your roost bars look like a square piece of lumber. If the edges are somewhat sharp, the chickens have a difficult time grabbing the bar, and sitting comfortably. Very much rounded corners/edges, or round bars are more ideal. Chicken can comfortably grab bar. I use round tree branches inside my coop.
You can test the comfort of roost bars, by wrapping a towel tightly around roost lumber, several times, and see if chicken feels comfortable on the rounded cloth perch.
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,