Is this the appropriate use of the word "an"?

An, since eight begins with a vowel. Doesn't matter how you wrote it, it's how you speak it. If you would write "an eight", then you would write "an 8", since they're both spoken the say way. And technically, the word doesn't even really have to start with a vowel... it just has to sound like it does. And that an honest answer. Notice how "honest" doesn't begin with a vowel? It sounds like it though, so you use "an" instead of "a" in that case too.