I have tried the store bought metal butterfly backdraft dampers with the 4 hot air collectors I have plugged into my house.
None of them were stopping the cold air backdrafts that happen when the sun goes away.
After doing some digging, I ended up finding a different Mfg. backdraft damper on the web that I liked so decided to copy their design and see if I could get good results.
After some trial and error with different materials I finally nailed the problem.
I made a pdf file showing the build which is
here for anyone interested.
A minimum of materials are needed to put these together..
