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I was always taught that in front of vowels and an H, one always uses an and not a. Please let me know what the correct usage would be.
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I think you are generally correct, though it depends upon the sound of the "h". "An" doesn't always precede a vowel. See the article: "Articles: A versus An" below.

I want a hot looking car. correct.

I want an hot looking car. Incorrect.

("hot looking" is slang for sexy or attractive....eg She's a hot looking girl...key word is "hot" She's hot, means she is sexy or special.)

I want to go in an hour. Correct.

I want to go in a hour. Incorrect.

Here are some additional references for you.

[url="http://owl.english.purdue.edu/handouts/esl/esliart.html "]Articles: A versus An[/url]

[url="http://www.rpi.edu/dept/llc/writecenter/web/esl.html"]Article Usage[/url]

Hope that helps.
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The only words that come to my mind right now in which initial "h" is silent are: heir, hour, honour, honest, and their derivatives. These words take "an" instead of "a".

Miriam