My personal opinion is not too, but that's just my opinion. I have silkies, de uccles, and a couple barred rocks. Did have sebrights till fox hit. If you decide to heat you could use a heatlamp SECURELY fastened in there. We get tons of snow and wind chills in the single and negative digits and...
How cold does it get in your area? I live in michigan and dont heat my coops. if your power goes out your chixkens will be in worse shape since they suddenly have no heat. Chixkens are very hardy animals. As long as you have plenty of ventilation and dry bedding they should be fine.