EcoRenovator - Hello from Low Sun Land

It is good to see so many familiar names here. It turns out that of the two projects sitting in my backyard, the solar panel got built first. I'm still driving the "bad" Metro instead of rebuilding the "keeper."
Anyway, I put up a 5 X 15' "false front" on one of my gables to catch some hot air. I'll post pics after it is working, unless I get bugged for construction shots. I'm aiming to insulate the back, and use cheap plastic to build the collector. Arches bent from lath will create one large duct running sideways and back, and adding the single strip down the middle will tension everything nicely.
Right now, I'm trying to think of the elegant way to attach the ducting. I've been warned that I might melt the plastic, but so far, a test section has only yielded 70C, so I shan't be too fussy about fail-safe fans. I'll put in an easy pop-off vent for summer.
The idea here is to develop something that works best as a retrofit on an existing south wall. It is vertical, to avoid collecting dust, and because that is close enough to the sun direction when it is needed most, especially up here at 53N. By using air as the working fluid, I have a bit more electricity turning into heat via the fan, but I loose all worries about expensive freezing or leaks. Once inside, the air will go over a junked truck radiator to warm water for a tepid water tank. If there is no temperature difference, the thermosiphon shuts down, and a flap prevents backflow. The rest of the heat will be delivered to the house via the normal furnace ductwork.