How cold is too cold to keep mom and new chicks in the coop

[ChickenCanoe]

The chicks are with a mom so they don't really need heat lamps and definitely not more than one.
Putting heat lamps on a mother hen in cold weather isn't doing her any good either unless you plan on keeping her inside throughout winter and never have power outages.

 

[Taylor39]

Our Silki hatched chicks about 3 weeks ago (Colorado). We haven't used any heat assistance during incubation or since hatching. They go everywhere with her, including foraging in the snow. When they are cold she warms them up and they go back to running around. We've had many nights into the teens (lowest was 9°) and had two blizzards, but even when the water freezes in the coop babies are still good in the morning. We haven't lost any!

Mama does way better than a heat lamp and babies are feathering much faster than the chicks we have raised indoors in a brooder. They are stronger, healthier, friendlier and so happy! I agree with everyone who posted that providing heat keeps the babies from getting used to the cold, our chicks are already getting a nice bunch of feathers.

Any research I have done indicates all our girls (including babies) should be fine until Temps get near -20, which does happen here (but rarely) so we're definitely keeping a watch for all our girls and especially the babies. Hope this helps anyone else in cold temps with babies.