Montag has been collecting books for a year. He doesn't understand why he has stolen the books from the fires he has set, but he did it. He also knows that if the governement --- or even his fire department buddies --- find out, he will be reported, his house burnt, and he will be arrested. He is hiding the books in the vent. On page 65 it says "Then he reached up and pulled back the grille of the air conditioning system and reached back inside to the right and moved still another sliding sheet of metal and took out a book". He had a total of twenty books up there.