Antminer S2 has a set of large front inlet fans. These suck a bit of dust, and outside a datacenter (meaning, in your dusty home), they will accumulate lots of dust very soon if you don't filter the entering air flow.
Here is a cheap, easy and instant solution : you can use one of these kitchen disposable hood air filter papers :
This is a perfect type of paper for air filters : almost transparent, very light, does not put any noticeable additional drag on your fan, and these have a rubber band, like a shower cap.
Now, they also have the perfect size to just fit in half a second onto the front part of the S2. And presto, your front air entry is filtered !
And the paper is nearly transparent, which has the added bonus of not hiding the LEDs or the LCD screen !
Of course, don't forget to stick a small piece of filter paper onto the PSU inlet fan, on the right side, as well.
This way, your S2 will keep its inside free of dust and will make you a long use.
