Which way to turn a knob to increase?

I'm making an app with a skeumorph knob that you can turn clock- and counterclockwise to increase/decrease an amount.

But what direction is the correct one? I bet that there is a high degree of cultural difference between countries/regions, and a high degree of difference depending on use-context.

I live in Denmark, and "all" common radiators have a knob for turning up the heat - you have to turn it counterclockwise to increase the heat. This might just be a radiator-thing or just a Denmark thing.

Let's say the app I'm making is controlling a radiator via wifi, should I follow the local norm, or just decide on a "correct" global way...?