There are 2 balloons in each zone (except for Orr and Southsun). There are a total of 44 balloons, but you only need to find 30 of them.
If you have trouble finding all of the balloons you can:
1. Talk to the NPCs with a telescope next to a star on your map in each zone.
2. Go to this page —-> http://wiki.guildwars2.com/wiki/Hot_Air_Balloon
3. Or watch this awesome video that shows each balloon —-> https://www.youtube.com/watch?v=gP_lIGU_VWc
Sidisen was here…