A long as they are dry and out of any drafts, they will be fine without a heat source.Or do you think not at all? We will continue to have cold snaps until March/April, sometimes being as cold as minus 10 Celsius (14 Fahrenheit). Just want to give them their best chance. I’d love to hear everyone’s thoughts about this as well
Here's a story that should convince you:
https://www.backyardchickens.com/threads/broody-in-michigan-winter.947046/