It sounds like you're talking about feeding crushed or flaked eggshells (or possibly oyster shells) to chickens for calcium. If they’re not interested in the crushed shells, flaked might work better, especially if mixed with their fermented feed. Some chickens can be picky about texture, so...
I would recommend you not clean out your coop during the winter as the nitrogen keep heat in the coop. i would also suggest feeding your chickens scratch also stapling tarps over the windows and calking and using pipe insulation for any places allowing cold air in your coop
i would recommend keeping manure as it keeps heat from the nitrogen i also highly recommend feeding them scratch. also seal any places that let cold air in with tarp or pipe insulation or calk. it also depends on how cold hardy your breed chickens are. i hope you found this helpful