Introducing chicks into a flock

[FrahmChicks217]

So I'm have 9 chicks that are around 6 weeks old and then I have 28 chicks that are between 3 and 4 weeks old. Will I have to keep my younger ones safe in a separate cage when introducing them? Or are they close enough in age it shouldn't matter? My older girls aren't out in the coop yet as where I live has been much too cold for them without a heat source.

 

[DobieLover]

How large is your coop?
How large is your run?
Can you post pictures?
How cold is 'too cold'?
6-week chicks are fully feathered and absolutely do not need a heat source as long as they are in an area protected from drafts.

 

[FrahmChicks217]

Our highs lately have been between 40 and 50° F. I don't have pictures of our coop and I'm out of town at the moment for the holiday. But I do know going off of the 3 to 4 square foot per chicken rule, we can fit over 50 chickens in the coop. And then run is around the same size but we we are currently extending out the run so it's longer.