Vent pipe freezes Home › Forums › Public Forums › Drainage & Sewerage › Vent pipe freezes This topic has 1 reply, 2 voices, and was last updated 24 years ago by SylvanLMP. Viewing 1 reply thread Author Posts 12 Dec 2000 at 7:30 pm #278801 Anonymous Whenever the temperature gets below freezing, our sewer vent pipe, which is through the roof, freezes and the sewer smell come back into the bathroom right below it. What can we do to keep the pipe from freezing? 12 Dec 2000 at 8:08 pm #299329 SylvanLMPParticipant Simple INCREASE the pipe Vent through roof (VTR) to 4″ diameter MIN. This will prevent HOARFROST. As the warm vapor from inside the building hits the cold out side pipe it had a tendncy of frezing against the piping walls. This is called Hoarfrost. no big deal to increase. Good luck Author Posts Viewing 1 reply thread You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In