[DavidU (Dave)]

That's what I thought.

Originally Posted by Starkler

The mechanism of heat transfer is quite simple.

Heat is transferred from the heatsink to the air surrounding it. This heated air needs to be removed by the fan so that cooler ambient temp air is adjacent to soak up more heat from the heatsink. Keeping a stream of air moving over as much of the heatsink as possible will give maximum heat transfer, therefore blowing should always be better.