My 17 month old has the same issue, he soaks through a shirt per hour! We took him to an ENT and it turns out he has enlarged adenoids that make nose breathing difficult, thus why he’s a chronic mouth breather/drooler.
If he is teething, then yes, it is normal.
I don’t think he is teething- I check when brushing and there doesn’t seem to be any new teeth coming through.
@Jenn this is interesting - maybe I need to check that out…
Is he teething?