Vent size reduction

[Denray]

Seems like this vent should not be reduced as it rises above the house, right?

[Chad Fabry]

Where it freezes, the vent diameter must be at least three inches to prevent frost closure. 

I'm not bothered by the change in size and I couldn't find anything that prohibits it- if water is running down the pipe it flows from smaller to larger. What probably limits the size is the number of fixture units. If I'm right and that's 2-1/2 inch pipe, just 6 FU's are allowed. If it's 3-inch pipe 12 FU's are allowed and it's probably OK for any normal modest house.

All that said, it probably works fine.

 

[Denray]

Thanks!

[Bill Kibbel]

28 minutes ago, Chad Fabry said:

Where it freezes, the vent diameter must be at least three inches to prevent frost closure. 

I'm not bothered by the change in size and I couldn't find anything that prohibits it- if water is running down the pipe it flows from smaller to larger. What probably limits the size is the number of fixture units. If I'm right and that's 2-1/2 inch pipe, just 6 FU's are allowed. If it's 3-inch pipe 12 FU's are allowed and it's probably OK for any normal modest house.

All that said, it probably works fine.

 

Chad,

Probably should stick with the standard abbreviation D.F.U., well, cuz FU.  

[Chad Fabry]

That was funny.

 

[mjr6550]

Regardless of freezing, I believe the IRC requires one minimum 3" vent. However, its an old house. I doubt I would have mentioned it.