I replaced some 30+ years old windows the other day. For three of them we had ordered an upper tricle air duct. Our house does not have any fans or balanced venting system. It's a wooden house with 99% electric heating. There is only hydro power stations in Norway, and that type of heating has had an ok price tag.
The air ducts have a barrier inside, so the air is really trickling. On the outside there is protection for rain and insects. But the inside cover that came loose with the windows was of extruded aluminum with two fastening plastic joints, one on each side. There was no way for any "remote" control, to stand on a chair was the only option. The aluminum was isolated on the side towards the vent, but I still assume that humidity inside could condesate on the relatively cold aluminum when it is really cold outside. I have also seen the brass covers, where two rulers with square holes overlap between more (open) or none (closed). Also weak on condensation I assume, and very difficult to remote control with only a few grams of pull. It would need much more, and both push and pull. So I wanted to make something else.
Wooden, that could easily be controlled without standing on a chair, and no surfaces to condesate on.
This post describes the three, all different solutions. All were made from birch with a thin round wooden rod or stick glued to the back. The covers swing on this rod. The center of gravity is outside the wall, so it's pressed to the opening, to keep closed. In other words, there has to be some pull to hold it open. And in open position the vent opening looks ok. The first solution is stable anywhere between open and closed, while the two others are open or closed only.
1. The upper row (above) shows the one that's controlled by twisting the curtain rod a quarter of a round. I use fishing line as thread, but sewing thread may be just as good, since the nylon seems to stiffen around the eye screws. The pictures may talk for themselves.
2. The above pictures show how it's done in the shower in the bathroom. The plastic curtain takes 99.9% of the shower's splash. However, it would be essential to make it easy to open and close the vent, and see the position - without removing the curtain. There is one wooden dowel pin on the top, and one "via"-point to shorten the wire. The left picture shows the closed situation without the plastic curtain, (removed for the photo), the right picture shows the open position with the plastic curtain (alway present). (On the left a drop drip silicon row is seen, behind the curtain.)
3. Here is the third solution. It's easily reachable while standing, so there is no wire. The left position is open, held by the brass angle (?) screws. I use those screws to just hold all the covers. The right picture shows the closed position, where the cover has been pushed to the right and fallen into closed position. There also is a locked position (with no picture), where the cover is pushed to the left. So the angle screw keeps the cover locked in both open and closed position. This could be ok it it's blowing a lot outside. The other solutions take no height for locking, so I'll just have to wait and see. But the barriere and the pressure by the weight also has quite some locking effect.
Search words in Norwegian: innvendig deksel for lufteventil i vindu