I was pretty shocked to see this on the front page so I think it's important to add that I really didn't expect more than a few people to find this duct adapter useful. I live in the UK and consider 25°C to be way too much hot. Plus, I'm using my portable aircon unit in an attic where the air temperature outside is actually comfortable, it's just that the sun on the roof and the air rising from the rest of the house is heating the room above outside air temperature. If this isn't the circumstance you're in, you may prefer to look at something like https://www.amazon.co.uk/dp/B083375CF4 instead.
I've made a couple of changes aimed at helping people print the full size version of this. I've shortened the thinnest (the rectangular) part to 100mm and heavily filleted the inner corners of it. You'll need to check that 100mm is long enough to get through the smallest gap in your window. There's also still a wicked overhang on the two lower parts so I still suggest testing your printer/filament first if you're not sure it will come out without needing support.
I've also renamed the smaller two adapter sizes to clear up any confusion about how small this reducer really is.
Plus .dwg files for anyone that can use them.
As lots of people have noticed, the original model is a ridiculous reducer at a ratio of about 3:1 from the original duct. I've now added a design that is much larger (labelled as "Full Size") and can be printed in three parts to fit on a standard Ender 3 bed.
The internal width is now 380mm - double the previous version. I've also increased the height of the opening by 2mm so the outside dimension is now 26mm. I advise really measuring your window before printing to be sure it will fit. This brings the cross-sectional area of the reducer to the same as the manufacturer supplied window-adapter that came with my unit - but just because it's OK for my machine please don't assume it's OK for yours.
The tabs on this design are pretty shonky but they are just there to hold the parts together while you glue them. Be sure to pick a glue that has a bit of flex in it and can take the heat exposure.
Please note, I've put this design up in a rush to stop anyone printing the original version without actively choosing to reduce their duct by as much as me. But that means I haven't had a chance to print it myself yet. Please take extra care to check the STLs in your slicer, particularly with the big overhang.
I designed this air duct to get the 120mm diameter exhaust from my portable aircon unit to fit out of my attic Velux windows without leaving a huge gap for my cats to sneak out of. It's a pretty standard unit so probably fits other exhaust pipes, but I've included STEP and fusion files so you can customise it. Watch out for the clockwise thread on the tube.
It's important to note that this adapter has a cross-sectional area around 1/3 of the original exhaust. This could restrict the airflow enough that the unit can't cool itself effectively. I've included a version with a 36mm rectangle height (instead of 24mm) and a shorter narrow length to combat this - but this will require you to move your window's stop hole if you still want to lock it in place. Either way, make sure you're comfortable with the consequences of restricting the exhaust from your ac unit before using either version.
I'm going to try making a version that takes up more of the available width for an equal cross-sectional area to the exhaust tube. It'll be in three parts most likely to fit common print bed sizes. I'll update this Thing when I've done it. Done 30/06 but it's in need of more work to make it fit together without glueing.
You may be tempted to cover the remaining gaps in the Velux window when it's partly open like this. In my circumstances, in a lukewarm country, I don't think there's much point. My attic gets hot because of sunlight on the roof and air in the house rising to the top, so air coming in from outside is not much of a problem.
It's not a detailed print so it's probably worth using a larger nozzle and layer height. I printed it rectangular end down, with long side in line with the y-axis to minimise wobble as the bed moved. A brim is a
good idea really important but a raft might actually be better. You should print it in a heat tolerant filament (e.g. PETG) and definitely not in black! (Yes, I printed mine in white PLA and it's been fine, but I don't live in a hot place).