Genie,

I have a few violets that I keep at the windows. I leave them there, year-round and have never had any adverse affects. A heat mat would keep them warmer if you are concerned about the cold. I have heat mats under my leaves in the winter and they work wonders.

Linda

I have over 2 dozen violets that stay on the window seats in my 3 big picture windows all 4 seasons. Some have been there for 6 years. I live in western New York where the overnight temps can drop pretty low. On unusually cold nights ( single digits) I move them out of the window onto nearby flat surfaces. The heat vents in the floor immediately below the windows keep them plenty warm the rest of the time. I just make sure the outer leaves are 1/2" from the glass.

I would move them a little away from the glass. I have big corner windows and I do not have central heat. It does get cold here. I use the small electric heaters that look like radiators and turn them on very low at night near the plants. It works really well.

I have clear shelving units in two windows in my plant room. These windows face south, but are underneath a wide, wide overhang so summer sun doesn't really hit them directly; I have more problems spring and fall when the sun is lower in the sky and then I use a sheer curtain between the plants and the glass to prevent sunburn. In winter, however, there is nothing between the (insulated glass) windows and the violets as I need all the sunlight I can get in our typically cloudy winters. We regularly have below zero temperatures during the late winter here in northern Michigan. There is a vent for the forced air furnace below the window and I do believe that the heat moderates the cold near the glass somewhat - but the furnace does not run a great deal, and at night I keep it set rather low so certainly it doesn't offset the low night temperatures completely. I never had any problem with any of the leaves being damaged, and you're quite likely in a warmer zone that I so I would think if mine make it, yours could too. Of course, don't let any of the leaves make contact with the glass, but your violets will probably be just fine.
You could always apply some of that clear plastic on the inside of the window to give a bit more insulation if you are really worried about your windows being cold or drafty. Just a thought.