If you're just wanting a slight warmth, I've read positive things about the Sweeter Heaters (flat panel type heaters - very safe). A red heat bulb, even the lower wattage ones like 75 or so, would probably provide more (direct) heat though, depending on your goal. I use one of the contained old heaters (that look like a radiator) in my walk-in coop and a clay pot heater in my bantam coop (regular 75-100W bulb in a clay pot). But my area doesn't get a winter anything like yours...thankfully.