Should "an" be used before words beginning with "h"? [duplicate]

Possible Duplicate:
“A historic…” or “An historic…”?

Should an be used before words beginning with 'h'? What about when the 'h' is silent and is followed by a vowel?

A rule of thumb is to use "an" only when you do not hear the h when you pronounce the word. See here: When should I use "a" versus "an" in front of a word beginning with the letter h?

A summary:

• If the h is silent, as in "hour", use "an".
• If the h is sounded and the first syllable is stressed, as in "hammer", we use "a".
• If the h is normally sounded but the first syllable is not stressed, it could be either "a" or "an", depending on the noun and the speaker. I think you will hear "an historical building" more than "an harpoon". Words in this category may be pronounced differently by different people in different places. According to our esteemed moderator Nohat, traditionalists would use "an" in this case (see the link above).

We should not when it is not silent. We say "a human" and not "an human".

However, we use 'an' when h is silent. E.g We say 'an hour' but not 'a hour'.