There are 242 Republicans in the 112th House of Representatives. All of the returning incumbents voted against Obamacare, and all of the freshmen should be expected to vote for repeal as well.
There are also 14 Democrats still in Congress who voted against Obamacare. (A total of 34 Democrats voted against Obamacare last year — three retired and 17 were defeated.) If they all repeat their performance, that's 256 votes for repeal.
Of the 7 freshman Democrats, all are likely to vote in favor.