I have 4 hens in coop roughly 7by8 and 7 feet tall. Its uninsulated. I secured a 250watt red heat lamp in there. I know some Don't use a heat lamp but im going to regardless. Anyways my question is that its been in the teens to twenties at night and so far they seem alright but tomorrow nights gunna be 1 degree. Whats a good judgement of temperature to go ahead and use the heat lamp?