Solar window heater update

I’ve been fixing the window box heater. It’s been working OK over winter but not to its maximum. I’ll rebuild it over Summer and add a temperature control so that it only comes on when the air temperature in the box is over 20°C. I’ll use thick glass as the cover instead of thin perspex as glass traps more heat. I’ll also make the whole box fit the front windows much more closely. That’ll mean making it longer, potentially doubling it’s length. This box was originally made for the chook run to warm that over Winter but it was too effective so I had to take it down. It is made from scrap and has coir flute as its backing and thin Styrofoam as insulation. I know how well it works and I’ve got much better materials now so it’ll be a real furnace next Winter. I also learned how to improve its heating ability. First, I repositioned the inlet

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Window box heater

Last year I started fiddling with passive heating and whipped up one of these window box heaters. I found several flaws with my design and have since learned how to improve the efficiency greatly. For this test, I just leaned it on the sill of the kitchen window (the most northerly facing window) in the sun. It’s about 15C today and this little box is pumping 26C while it’s in the sun! My (not really passive) version has a two small solar panels that I rescued from somewhere last year that power a small DC fan and a temperature switch. So, how to improve on this design? Firstly, the temperature switch is redundant, mostly over-engineering for its own sake. The inlet and outlet holes were cut so the box would work in a window that we’ve found to be better closed and insulated in winter. They’ll have to be redone so the inlet is on the inside of the kitchen

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