Windows in your home have been known to let heat seep out, but by building your own Heat Grabber, you can reverse the process! Amazingly, this solar collector can cost you as little as a few dollars per square feet and a couple of hours (or less for real handymen out there) for a device that will give you years of dependable service.

The key is Thermax TF-610, a rigid foam insulation made by Celotex. A strong piece of hardware with glass fibers and heavy aluminium foil on both sides makes this ideal for quick and easy assembly of a Heat Grabber. Despite its strength, Thermax is malleable enough to work with that you won’t need any unwieldy saws or hammers. Actually, it’s possible with just standard knives and measuring instruments. Follow the instructions on the blueprint here, and you’re just four steps away from this miracle device! Take into consideration the size of the window you are outfitting when cutting and building, as well as when you set out for the materials you’ll need, listed below:

  • 1 sheet of 1″ x 4′ x 8′ Celeotex Thermax TF-610
  • 1/2 sheet of 3/4″ x 4′ x 8′ Celotex Thermax TF-610
  • 1 tube of Liquid Nails panel adhesive
  • Silicone caulking compound
  • 16 No. 8 finishing nails (scrounged)
  • 3 sheets of single strength glass cut to fit
  • All-metal aluminum foil duct tape
  • Rustoleum flat black paint

The Heat Grabber works by hanging this insulated, weathertight box over a windowsill. When the sun shines, the rays pass through the glass on top of the Heat Grabber and warm the aluminum foil covering on the upper surface of the divider (which is painted black to accelerate warmth generation). As the foil heats up, it warms the air which rises up and flows out the opening at the Heat Grabber’s top. A “lip” opens up into the house, with the window closing snugly over the glass which covers the top of the Heat Grabber. By also pulling cool air from the base of the device and warming that up too, the Heat Grabber is able to form a “convective loop,” heating your house all hours of the day and asking nothing in return except for the sun’s energy. When you can’t deliver that, the loop is halted. Cold air sinks to the bottom, so you won’t need to worry about warm air being pulled from your house on cloudy days. To get the most out of your Heat Grabber, position it at a southfacing window (for those of us in the Northern Hemisphere, otherwise, it’s vice-versa), at an angle that is your latitude +10.