Make a DIY solar Air Heater. The beer can and pop can heaters are a waste of time. Using corrugated HDPE used in this video for the solar thermal forced air heater has excellent surface area and is very affordable. This set up can be enhanced with mirror base or enclosure for a smaller footprint on your roof.
HDPE High-density polyethylene is inert at lower temperatures. The operating temperature is rated above 200 f. Below 140 f the material is good for this application. With higher air volumes, it is unlikely you will reach above 100 f on a cold day.
HDPE has little branching, giving it stronger intermolecular forces and tensile strength than lower-density polyethylene. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength. It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C/ 248 °F for short periods, 110 °C /230 °F continuously).
▪ Geothermal heat transfer piping systems
▪ Natural gas distribution pipe systems
▪ Water pipes, for domestic water supply
This is the easiest forced air solar heater you can make. The fan is a bilge vent fan that costs $30. The 4" HDPE used in this video is $3-$5 per 10' section or you can buy 100' rolls for $45.
The 4" bilge fan fits perfectly and is rated at 150-175 CFM.
For hyper-cold climates with wind, this can be placed in a box with glass covering.
Air volume verses high heat.
It can be quite impressive to see solar thermal panels reach high temperatures above 150 f but it is of little use for domestic air heating as these temperatures are not sustainable with the proper air volume flowing through the system. Higher air volume is more efficient at air mixing reducing leaching into the surroundings.