Merriam-Webster's Dictionary of English Usage is more descriptive than prescriptive, but it advises, "You choose the article that suits your own pronunciation." Theodore Bernstein gives the straight vowel-sound vs. consonant-sound explanation but allows that one should indeed say "an hotel" if they think hotel is pronounced otel.
To avoid confusion, perhaps we should all consider using "an H.S.A." or just 'h-s-a" (see below) I tend to use "an HSA" exclusively, using the "an" to signify that a hard letter pronounciation (H in this case) follows (e.g. An FBI agent...). That being said, I think "a hissa" would also be correct because the period are missing between the letters (but marketing would never listen). When I do not see periods between letters I tend to pronounce what follows as a word rather than reading the letters, except when "an" is used.
I.R.A. was shortened to IRA.
FWIW, there is only one instance of "a HSA" in the 3rd Edition of the HSA Anwser Book. [I'll correct that next year.]
I once globally replaced "a health savings account" which I wrote a few hundred times with "an HSA" and it worked just fine. I've also learned to stop Word from changing "HSA" to "hsa."
QUOTE
I play "An Harmonica".
Does that count??
Unquestionably it would; especially if for someone (not you) that thinks "Harmonica" is pronounced "AYE-monica." <grin>
"Y.M.C.A." (lyrics)
Young man, there's no need to feel down.
I said, young man, pick yourself off the ground.
I said, young man, 'cause you're in a new town
There's no need to be unhappy.
Young man, there's a place you can go.
I said, young man, when you're short on your dough.
You can stay there, and I'm sure you will find
Many ways to have a good time.
It's fun to stay at the
y-m-c-a. It's fun to stay at the
y-m-c-a. ...