How durable is the solar air heater? 

It worked at temperatures below -25°C ( -13F) , and tolerated temperatures below -42°C (-43F) in the winter of 2017!

It was a fantastic experience with the 19+PV model in Jan 2018. The temperature reached -30°C (-22F) for many days in Quebec in late December 2017, however, the real freeze hit at about -42°C( -43F). The collector was exposed outdoors with no connections for testing purposes, it was a test of the heater’s durability, and the results were better than expected. Even though the collector was covered by snow while it was outdoors, immediately it was cleaned we started hearing sounds indicating that it was up and running again, it was still alive, and well even after the ordeal it had just gone through.

Photos for the solar collector before the storm in November ;