cheaper fix and that is particularly for night time when you want to warm up you make insulated kurt tains for the windows. roll them up in the day when you want the light. when the sun goes downoir when it gets dark roll them down and seal them and you will be done. you can make them at home. you can have somebody professionally make them and they will look better depending on your sewing skills. i did that had i was a tenant living in an old victorian in oakland i made my own window and borrowed i sewing machine and put it together and you can do it and will make an impact on the window. you can go to any of the websites like homeenergy magazine and from there you can find how to make your own kurt tains. when they say insulated curtains what it has is a vapor barrier in it so the warm, moist air in the house doesn't come into contact with the glass and you don't get the condensation in there. the heat that's in that moisture is helping to keep your space warm. when it hits the glass it radiates the heat directly out the window. in order tow keep that you want to be sure jour curtain has