After successfully dual-booting fedora on my Macbook Air, i have noticed that the Macbook tends to heat up a lot faster than when I am using Mac OS X.
Is this normal?
No, I don't think it's "normal". But as always, it depends. For me, this usually happens when I look at full screen flash video or am doing other computing intensive stuff. When I dualboot into my dev environment, I'm just surfing the web for informations which wouldn't lead to the heat up.
TL;DR: It's very likely that it's your behaviour that changes with the platform you boot into and that it's this causing the heatup.