Anyone have any experience with if the rooms at CMC are generally chilly/comfortable/warm?

Comfortable. Some along the sunny window side can get a little roasty in the afternoon, but the windows do open for ventilation.

It can get cold on the shady side, but not often. I think that was the year I walked through snow in Brussels to FOSDEM, so probably 2021?

rooms at cmcmcmc are all over the place, if it's a full room it gets steamy, then when windows get opened in the winter it gets really cold next to them, yet still steamy on the crowded/sunny side

Thanks everyone

Any coat check? (Do I bring the big heavy jacket or not)

There is a coat rack opposite the entrance doors. We just leave coats and cases there, only us in the building.