Heed the above advice...please!
CX in a closet with the door closed is a recipe for disaster! Poor ventilation and warmth is a good way to kill your birds...these CX aren't like other chicks and don't require nor thrive on the same amount of heat. If you open the closet door you will not be able to live in your home...the smell is really THAT bad. Also....have you seen the size of 3 week old meaties? No storage container that would fit in a closet would possibly contain 12 of these birds at 3 wks. of age...or even 2 weeks.
Your best bet is somewhere with very good ventilation, a brood lamp that isn't too close to your chick floor....just watch how they sleep, if you see piling just move it closer. These birds overheat quickly and will die of heat exhaustion even as little chicks, so watch also for laying about and panting, not eating or drinking. If these birds ain't eatin, they are stressed!
Just follow this link and take a look at Post #30 for a gander at what size your chicks will be at 3 weeks and this should give you an idea of the size of brooder you will need. Actually, you can read the whole thread and it may give you a little insight into their growth rate from the beginning so you will know what to expect.
https://www.backyardchickens.com/forum/viewtopic.php?id=325493&p=3
Your best bet is somewhere with very good ventilation, a brood lamp that isn't too close to your chick floor....just watch how they sleep, if you see piling just move it closer. These birds overheat quickly and will die of heat exhaustion even as little chicks, so watch also for laying about and panting, not eating or drinking. If these birds ain't eatin, they are stressed!
Just follow this link and take a look at Post #30 for a gander at what size your chicks will be at 3 weeks and this should give you an idea of the size of brooder you will need. Actually, you can read the whole thread and it may give you a little insight into their growth rate from the beginning so you will know what to expect.
https://www.backyardchickens.com/forum/viewtopic.php?id=325493&p=3