
Ten ounce cans
Disposable Duster, 10 oz 2-pack
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$13.44$0.67 an ounce of gas
Two standard cans keep one ready on the bench while the other rests in a desk drawer for keyboards and towers.
Intake grilles, heat sink fins, power supply cages and the fan blades behind all of them.

A fan spun by a gas stream turns into a small generator, and that is not what the bearings or the board were designed for. Put a finger or a pencil against the hub before you spray.
A year of intake dust does not disappear when it leaves the case. Take the machine to a doorway or a garage, or you will be cleaning the room next.
A tower that has been running in a carpeted room needs a lot more gas than a keyboard does. The 12 and 17 oz cans exist because standard cans were being emptied on single machines.
Start at the top of the case and work down, front panel filter first, then the heat sink, then the power supply cage, then the floor of the case. Anything you dislodge falls onto what you have not cleaned yet, which is the point of going in that direction.
Blow the heat sink from the far side so the felt comes out the way it went in. Blowing into the fin stack from the fan side packs it tighter.
A machine with front filters wants a look every couple of months and takes two minutes. A machine without them wants an hour once or twice a year, and the hour is longer every year it gets skipped.
Watch the fan noise rather than the calendar. A tower that has started to sound busy while doing nothing is usually a tower with a blanket over its heat sink.