Are you using a heat lamp or a heat plate?You could set up your brooder all ready for the chicks, and make sure that it stays 100 degrees by the heater all night. There are nice indoor/outdoor remote thermometers that I use for this. If it can stay @ 100, you are good to go.
They are very different.
100°F is too hot under a heat lamp.
https://www.backyardchickens.com/articles/aarts-chick-heat-blurb.75619/
@BobbieB7 Please show the exact heat plate you are using....a link would be good.Well it’s freezing her so garage is cold. The Brooder is like a little tent that they go under.
Has switch for brooder and one for coop heater
So must be 90* for brooder.
We are supposed to warm up a bit.
I’m getting mixed advice.
Some say they have their brooder in unheated coop and use the heater others say to cold for them
Some plates are not recommended being used where ambient temps are below about 50°F. Sometimes they may work OK in colder temps, sometimes not.
What is the exact temp in your garage..and is garage attached to house?