That's to do with the two different "h"s in French. The "h muet" (most of them) and the "h aspiré" (still quite a lot). The muet ones are pronounced like they start with a vowel and for the aspiré ones it's like they start with a (silent) consonant. So basically for every h word you need to know which "h" to use (very difficult except for the common ones, lots of the aspiré ones are foreign words though). Some examples of "h muet" are l'hôtel, l'heure, l'hôpital ... and some examples of "h aspiré" are le heros, le hamburger, la hauteur and le hérisson (and so it must be that Hanoucca falls into the "h aspiré" category of h words)