Passive Solar “Sun Grabber”

*NOTE* After a few sunny days of operation, the inner plexiglass pane warped and ruptured. We would recommend using real glass panes, at least for the inner pane if not for both.  

There are plenty of designs available online. We drew from two sites: and The idea is that the sun heats the air in a box. The warm air naturally rises, and is channeled into your house. This convection pulls cool air from your house into the box; the air is warmed and flows up into the house, drawing yet more cool air into the box…………


Here are some step by step photos:

  1. First we built the two side pieces

  2. and attached the bottom sheets of plywood:

  3. We lined the bottom of the box with 1″ thick foam to insulate. The small squares of wood along the inside of the box are for screwing the middle piece of plywood into.
  4. The middle piece of plywood goes all the way across, so the side foam insulation had to be done in two layers. Shown here is the bottom layer before the plywood shelf was installed.

  5. And now, with the plywood shelf. We covered the shelf with aluminum foil, hoping that it might reflect a little heat back up to the air. This may have been wishful thinking.
  6. We bought flashing, corrugated it ourselves by creasing it on table edges, and painted it black. Then we stuck it into pieces of 1″ foam that will be the side-wall insulation on the top half of the box (above the shelf):
  7. Here it is with the metal and foam placed into the box, on top of the middle shelf.
  8. A wood frame to separate the two sheets of plexiglas that go on top of the box.
  9. Almost there! This is the whole thing put together, missing only the last, small sheet of plywood that goes on top of it all.
  10. Plexiglas layering up close
  11. Installed! From the inside


  12. From the outside. (The upstairs bathroom had the only workable window on the south side of our house.)