I had a busy day yesterday as I removed two crawl space vents with a chisel, pry bar and hammer; I replaced them with an automatic vents (pictured at left (opens at 70 degrees and closes at 40 degrees)). I put them in the freezer to make sure it worked (it did) and then I placed them on the floor and they opened back up. You have to make sure when you put them in not to twist them when you tighten them in (if you twist them they bind and will not work). I will have to check them when the weather gets below 32 degrees this fall.
After I did that I rested until mom went to a Meeting at 1200 noon. While she was there I finished mowing then picked up the grass clippings. By the time I did that I was tired and sore and mom came home from her meeting.
The vents have a coil like the old thermometers that move at temperature changes.
"A bimetallic strip is composed of two different kinds of metals that have been bonded to each other in a strip. Since the metals react to changes in temperature differently, the strip will curl in one direction or the other (or curl and uncurl, if it is formed into a coil). This can be used to make a transfer that reliably reacts to changes in temperature."