Thanks, and good luck with your self made hot air heating box ventures.

I recently completed a solar hot air panel that’s kicking out 130 degrees when the sun is on it…
I have it setup with a Snap Disk controller so Fan comes on automatically at 113 degrees and shuts off when the temp drops down to 90 degrees.

I built it out of pressure treated 2×4 frame / size is 4ft x 8 ft
I put 1/2 inch styrofoam with foil both sides on the inside of the box and on the inner sides of the box then covered the top with that rippled roof plastic you can purchase at Lowe’s or home depot. I have 2 4 inch tubes for supply and return. I also installed 2 baffles inside to force the air to move slower from one end to the other so it would heat up better.

My conclusion is that if you build one of these go with a 6 inch duct booster fan rather than a 4 inch booster fan. The 4 inch just wasn’t powerful enough to extract all of the heat out of the unit.
The 6 inch fan actually never shuts off either until the sun goes down so I might try changing it out with a 8 inch fan… but man what a heater this thing has proven to be.
Heavy as heck, but works super. I’m building a much lighter design one now.

I’m making the frame on the new one with steel commercial studs that they use in the commercial buildings instead of 2 x 4 wood studs. This new unit I’m using 2 x 6 metal studs. I purchased 2 10 footers and cut each one 2 ft from the end then folded them in to create a box 2 ft x 8 ft in size however because of the depth is deeper on this new metal box the sq footage volume of air will be almost as much as a 2 x4 pressure treated wood heater 4 x 8 ft in size..

I attached the clear plastic roofing material today for the sheathing and got it almost wired up for a test run tomorrow afternoon.

Write to my email anytime if you have any questions.

I purchased the snap disk controllers on Ebay
Purchased the 2 x 6 metal studs from a local commercial building supply store.

I forgot to mention I inserted aluminum flashing in the metal box first.. then 2 inch styrofoam insulation board, then more 2 ft wide flashing on top….// painted it flat back high heat paint and away ya go!

More info on passive solar can be found here:
http://www.solarpowerbeginner.com/passive-solar-energy.html

I really would like to know.

Regards