Insulated Blast Gate

Its winter here in Canada, and I was looking for a way to vent my printer out of my apartment window without crazy heat loss. My solution was to remix Jimbobareno's design, make it work for a 3.5" duct, and thicken the spacer so that the slider could be backed with a 1" piece of foam insulation.

I haven't actually tried it yet, but I will post some pictures when I have.