It is the whole House. Right now, there are 221 Republicans and 212 Democrats. So 289 votes are needed to expel Santos. You can safely assume that all Democrats will vote to expel so the Republicans will need to come up with 77 more votes. This is a little over half. If half of all Republicans can't agree on this, it will fail. A little over a third of Republicans would need to vote for this.
Edit: 289 votes are needed, not 325.