I have found a great solution for creating passive heat in the winter months. It's a vertical blind that can generates its' own heat. It's called SolarChoice Heaters. According to Bob Vila, "Most window blinds are used to keep the sun - and heat - out of the home. These SolarChoice blinds do the exact opposite - they increase the heat in the home." These innovative solar heaters look like vertical window blinds but do something no other blind can do. They can heat homes using only the energy of the sun. According to research conducted by the University of Minnesota the heaters generate 5.5 BTUs of heat per square inch. So, an installation on a typical sliding glass door is capable of producing 40,000 BTUs of heat per day. The magic of how the heaters work is part of their appeal. A "chimney effect" is created when the sun heats the aluminum core of each heating vane. As the aluminum core heats, cool air is drawn into the bottom of each vane. The air travels up and along the metal insert at the rate of 1.2 meters per second according to the university report. The report goes on the say that in that brief amount of time the cool air is heated up to 120 degrees and exits the top of each vane and re-circulates into the room as free heat.