Butter wrote:
Most of the descriptions say it has some kind of wax in a cylinder. When temp gets to about 55 to 70 degrees it melts forcing rod against greenhouse vent. I'm wondering how to make something instead of paying $60 ea. What kind of wax could this be. Doesn't seem like melting would make much pressure. Some of these automatic vents push out 18in
I need to automatically open vents when it gets too hot. Forgetting to do it manually just once will be the end of all the plants in greenhouse.
I discovered that after retiring I can't afford to spend money anymore. I'm building a greenhouse so wife, who is still working, will not get tired of leaving me to goof off everyday.

not sure exactly what's inside as the magic substance, but here's a
cut-away diagram of one

http://www.rostravernatherm.com/thermal-actuators.htm