The choice of a(n) before sounded h is based on stress: where the first syllable is stressed, it's definitely a full consonant, so a hat, a home, a history.

When unstressed, usage varies. The older method was to use an: an historic event. I think most of us now would say a historic event.

My brother Esau being an hairy man is clearly so said (Peter Cook, wasn't it?) for comic effect, and I doubt it had been seriously said before a stressed syllable for hundreds of years.

The OED in fact says it was so used until after 1700. After scanning Jane Austen long enough to get the suspicion that she was avoiding the issue, I found 'a house'.