I put my 32 chicks out 10 days ago when they were three weeks old. They are in a framed chicken wire and lattice brooder in the coop with the big girls. The brooder is on the floor under the roosts for the big girls. We have a tarp (poop hammock!) under the roosts so that the poop doesn't fall into the brooder.
The weather here has been all over since they've gone outside...some daytimes as high as 80 and as low as 45. Nights have been anywhere from 30-50 degrees. They have a 250 watt red lamp with a rheostat so that I can adjust for less heat/light on days when it has been very warm out. I found the rheostat at Home Depot for ~$12. We also have a camera (audio and night vision) from Harbor Freight $30 and a remote temperature sensor from
Walmart $10. So from my office in the house I can monitor them visually (hubby hooked up the cam to a $5 tv from the thrift store), know how warm it is under the lamp, and I can adjust the amount of heat they need with the rheostat. Being able to turn the tv on and see if they are huddled under the light has been helpful. I've also placed the feeders and water bottles within the range of the camera so I can monitor when things are running low.
They've been doing fine, seem happy to have a larger space (rabbit cage in the house vs 8' x 4' coop brooder), are very exploratory about the hens and the view to the great outdoors (some days have been warm enough to leave the big doors to the shed open), ...generally happy little girls. I had a bit of feather picking yesterday when the red light bulb burned out and I had to pinch hit for one day with a white light bulb. I would suggest keeping and extra 250 watt red bulb on hand just in case. That's also the nice thing about the camera and temp sensor...I can see if the temps go really low and observe the behavior so I knew right away that the bulb had gone out and the birds were getting cold.
After brooding chicks in the house for the last 3 years, and keeping them in until they are about 8-10 weeks old (big enough to take care of themselves with the existing hens), I really needed to find a better way. The brooder boxes were always in our office where are computers reside and that is definitely not a good combination. Not to mention the amount of dust generated cannot be healthy for the birds or the humans.
So I vote for putting chicks outside if you can, but have plenty of backup for keeping them warm, fed, watered, and supervised. If you can't do that then keep them inside until the are physically large enough to put with existing hens.
