Folks underestimate how tough a baby chick really is. After 2-3 days old, they spend lots of time out from under momma, no matter the temp. I try to mimic that (the ecoglow does a great job, in case anyone reading this wants to buy me a holiday present) and my chicks feather out nicely and are hardy.
Mine seem to love the EcoGlow, but I do wish I'd bought the 50 rather than the 20 (now that they're a few weeks old, 13 of them don't fit under the 20 and of course it's getting colder each night.