I have a similar question as others but I felt wrong taking over their threads. The project is an casing for electronics that will be outside all year around. Built out of metal. This means rain, sun, snow. -20c to +35c. The electronics inside works only in 0c-45c and 10%-80% humidity. I want my box to be airtight to not get any dust in. I will have a pc fan in the back that sucks hor air out. But I don't want an intake due to dust and maintenance of filters. The question here is how well the fan will work as I don't have an air intake? I am working on a one way valve for the fan so that I can make if stop at +10c or something to keep the heat in. If I stop it at +10c will the humidity go up in the box even if the heating is on? Heater will go on and off depending on the outside temperature to not get condensation. The casing could have two layers. First the box that is supposed to be airtight. Then a 3-5cm space abound the top and sides and then a metal cover over that. So its two layers with air in between. Would this help against heat from direct sunlight?