We are having a cold day and night here in Dallas, around 20F tonight. Maybe not so cold by other standards. I have an urban beehive that is going through its first winter and has a good supply of bees and honey with a 3 hive body stack and top feeder with winter mixture of sugar syrup. It is on cinder blocks about 8" off a mulched garden. I have put cardboard around the 'openings' between the cinder blocks to reduce wind chill effect. There is still lots of ventilation around the cardboard. And I have thrown a few thick towels over the top and sides of the hive as well. Would there be any benefit or harm in putting about a 200W resistive heating element on the ground below the hive? I placed one there and tried it for a bit and I suspect the air just above the heating element might be 60F after about 30 minutes of use. I realize I don't want to fool them into thinking it is OK to leave the hive. I suspect it might raise the temp inside by 20F. I can't find much reference to heating bee hives except for a patent from the 70's.