Four weeks is too young !! I am a relative newbie here but I have studied a lot of threads. One thing you must be very sure of is
that your babies have fully feathered out. A chicken's lungs are close to their backs. So they must be fully feathered on their backs
or could easily catch a cold... We live in the Shore area and it's just too unpredictable this time of year.
Our babies are 7 1/2 weeks old. We keep them in our spare bedroom in a Chicken Hutch. We shut off the red infrared heat lamp yesterday
for the first time. Because of them we have kept our house at 72 degrees, they did just fine, actually without the light they slept much
better than before, all night.
This is our first set of babies and we are being understandably careful. Yes it is a hassle having them inside all this time, and yes I clean up a lot of messes, but we don't want to lose a single one of them. We have learned that next time we have babies we will wait until it is warmer to get them. Say early Spring so when they can go out we will have warm weather for them, and we are getting a larger insulated coop with wiring for heat lamps.
Wait and take best care of them. You will be rewarded for your patience.