- 1). Cut a section of plywood the width of the window opening and the height from the window ledge to the ground at a 30 degree angle. The panel will lean against the window ledge and rest on the ground; it should be oriented towards the sun or have southern exposure.
- 2). Attach three measured and cut 2x4's around the edge of the plywood by using wood screws, creating a shallow box. The open end will be the "top" of the panel where the window venting will take place. The 2x4's should be on their edges, making the panel four inches deep.
- 3). Cut and place four six-inch sections of 2x4 lumber on the inside of the panel at the corners, flatly against the plywood. Secure them with screws or adhesive. They should be half as high as the depth of the panel, or two inches.
- 4). Cut a slightly smaller section of plywood and place it onto the wood blocks on the inside corners of the panel. Slide the plywood to the "top" of the panel, leaving a gap at the bottom, and secure it with wood screws to the corner rectangles. The result is a sandwiched air gap, with a space at the bottom for air to pass through.
- 5). Paint the visible area of the panel's interior flat black, and allow it to dry. Cover it with several coats until all surfaces are dark.
- 6). Secure a section of plexiglas to the 2x4's edge, sealing the panel together with adhesive or drilled holes for wood screws. This clear acrylic section will allow sunlight to pass through to the black area, heating up the air trapped inside.
- 7). Lean the top, open end of the panel to the window, directed at sunlight. Scrap plywood or measured and cut sections can be used to vent the airstream properly. Viewing the panel from the inside of the room, the top air gap is the hot "output", and the bottom is the cold "input". These can be vented in a variety of ways to place the warm air directly where it has maximum effect. Keep the hot vent above the cold vent, as the warm air created at the front of the panel draws the cold air through the gap at the bottom, and therefore the bottom vent. If the air at the bottom vent is warmer than the air at the top vent, the panel will not function correctly.
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