Quote: Agreed. Plastic and heat are a bad combination. However, I have a confession to make. When I'm hatching chicks, I will move them from the bator to a 24 hour brooder that is set up with a small MHP. I tuck those hatchlings under the MHP so I can keep an eye on them, and monitor for any neonatal health issues. I consider it to be the NICU of the poultry world. When the last chick in the bator is dried off, it's time to move the whole brood to a larger brooder. Again, MHP style. I favor appliance boxes. The large size lets those babies get plenty of exercise. Usually, I set the appliance box up in my garage. No heat, just MHP, and a nice thick layer of shavings. (they get paper towels in NICU. After a day or two there, it's out to the grow out coop. Temps during my brooding season can go down to mid 20's and possibly lower, with the high on a rare good day getting up into 60's. Chicks do just fine with only MHP for heat. By the time they are 2 - 3 weeks old, they are flitting around throughout both levels of that coop. (32 s.f. in their brooder level, and 64 s.f. in the lower deep litter run level.) They remind me of a flock of parakeets. When I go in to tend them, it's not unusual to have them bouncing off me.
I think a good rule of thumb is a minimum of 1 s.f. of open space per chick for the first week or two. Add extra space taken up by water and feed containers. By the time they are heading into their third week, they should have a minimum of 2 s.f./chick, IMO.