We've got two major factors going in getting this total to go Over. 
The first is an Astros offense that had the highest batting average in the majors and was third in runs and homers. They get to face a bunch of Tampa Bay relievers as Rays manager Kevin Cash is using this pivotal Game 4 as a bullpen day. First up for the Rays is Diego Castillo. He had a 6.14 ERA in six regular season starts. Castillo has never started a playoff game. 
The second factor is the Rays coming off a 10-run game against Zach Greinke and now drawing Justin Verlander on three days rest. The 36-year-old Verlander hasn't pitched on this short of rest all year. Tampa Bay has scored at least four runs in 19 of its last 25 games.