Busch Solar Heater

What to do with 90 -16oz Busch beer cans, empty of course. This is a thin shelled veneer box lined with 1-1/2" insulation foam. A 3/4" hole has been punched into the bottom of each can to create a hollow 10-high cylinder when stacked. Air inlet holes 3/8" were drilled through to the base of each column and the row of 9 holes was covered with fly screen. The columns are held ~1" above the insulation on the bottom. There is ~1-1/2" space above the columns. Hot air escape is through 3, 1-1/2", holes centered under a 12" x 4" shop vacuum head. The head is epoxy sealed above the holes. The exposed sides of the cans are sprayed with black primer, except for the label on several cans that were taped over to preserve their identity. A clear plastic roofing panel was cut to size and screwed and sealed to the box top. 

I set the heater outside for ~10 minutes on this 90+ day. After a few minutes I measured with my IR laser probe 107F at the bottom and 142F at the top. During cold mornings I expect the convection heater to exceed 50 degrees differential. A vacuum hose through a window to the outside, southern facing box should take the chill off the early air in the garage. A small 12v box fan inserted in the exhaust line may provide increased air flow without depleting the heating value. 

Thanks, Chris, for the idea. I'll post later in the season re how it really works. Out of pocket cost, net of the scrap materials, screws and the once full beer cans, was $21 for the piece of roofing from Lowes. 

Today, outside air is 60F and inside temp is steady at 190F; using probe thermometer. Box on head contains 12v box fan which creates a small additional flow of air. Standard vacuum hose connects to the output. Laser probe appears to be reading temp of plastic cover. Net gain is 130F. Larger input holes may increase flow volume.