Being a cheap-skate, I am incredibly excited about doing anything I can to put a little extra green in my pocket.  I have been looking online and thinking a lot about making a solar furnace to supplement our home heating.  We happen to have replaced 2 screen doors with full-length windows so I was presented with a couple of large pieces of tempered glass.

You can look around online for solar furnace or passive solar heat and find tons of additional information, but basically, these things work by capturing heat and using the principle that hot air rises.  I snaked clothes dryer exhaust tube side-to-side through an insulated (with sheets of styrofoam insulation) wooden box.  I covered the insulation with roofing felt to make the inside of the box black (plus I knew roofing felt would live through high heat).  I painted the box and the dryer hose with flat black paint so it absorbs heat very well.

Cool air from my family room floor is pulled in to the bottom of the system.  The sun heats it as it sits in the tube.  The heating causes it to move upward eventually running back into my family room at about waist-high level.

This version does not show a blower on it yet so air flow depends purely on the principle of hot air rising.  I am working on a version that uses a small fan powered by a solar panel to move the air.  I’ll post more on that later as I get the details worked out.

Anyhow, for the results…I set this in the sun at about 4:30 one afternoon.  The input temp was stable at 62.8 degrees F.  I then measured the output temp.

I could not believe it but my digital thermometer maxed out when the temperature got over 160 deg F.  The last picture I took before it maxed out was at 157.3 deg F.  I have no idea what the temperature actually got to but I saw at least a 100 deg F temperature differential!

I have some more info to post on this but it will have to wait until later this week…