After Beatty confronts Montag and explains that he has been under surveillance for a long time, Montag is forced to burn his own house because of the many books inside. However, since he is allowed to run the flamethrower himself, he chooses to start his burning with some other things:
...the twin beds went up in a great simmering whisper, with more heat and passion and light than he would have supposed them to contain. He burnt the bedroom walls and the cosmetics chest because he wanted to change everything... that showed that he had lived here in this empty house with a strange woman who would forget him tomorrow...
(Bradbury, Fahrenheit 451, Google Books)
His fear and misery in being forced into destroying his house and books turns into anger and fury at his life, wasted with destruction instead of construction, and with his wife, who barely cares if he is home or not. He destroys everything that reminds him of her, especially the television walls that he spent so much money on; she was the only person who appreciated them, and not his hard work to get them. His metaphorical destruction of his past life is a gateway into his future, even though he doesn't yet know if he will survive that long.