Does it have to be 29 for either candidate or 29 between the two?
29 votes for ANY real person who is a US citizen that is not Boehner, will force the second vote.
However, any “present” vote is not counted as a vote at all. If there are enough of them, then Pelosi could be made speaker! If your congresscritter votes present, it is time to primary the anti-american marxist!