Hello, I have a question regarding horizontal vent lengths. I am trying to tie my vents in to a vent header to have them share the same roof vent. I have stayed under my total fixture units for the size of vent. I have a 3" roof vent and captured most of the fixtures on that before stepping down to a 2" vent to finish the eastern side of the house.

In doing so I have ended up with a 37' run of 2" vent to capture the kitchen sink. It is a single story house, so there is not a great vertical run to speak of. When I have found information regarding the maximum allowed length of a 2" vent the consensus is 40'. I have stayed under that. Some information regarding this matter notes the horizontal vent to only be 1/3 of the vertical rise. This is where I start to get confused.

My question is can I run a 37' vent of 2" material WITHOUT having the vertical rise as some mention? It is a single story home and no great vertical vent to speak of. Thank you in advance for any and all information provided.

a vent needs to be (back) pitched towards the fixture(s) served to permit the flow of internal condensation

your description of your job is good to go as long as you maintain 'some' pitch

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

(Unless local code states otherwise)

According to the 2017 Idaho Plumbing Code, Table 703.1 allows 120' total length on a 2" vent and 60' on an 1 1/2" vent. A maximum of 1/3 of those lengths are allowed to be horizontal. Note 6 states that if you upsize the vent pipe 1 size larger, there are no maximums. If your total vent length is 120', your 37' is less than the 1/3 maximum. The kitchen sink only needs an 1 1/2" vent, you have upsized it to 2", so there's no maximum lengths.

Chapter 9 Venting - 905.1 states a horizontal pipe can be installed level or pitched back towards the drain it serves, so you do not need to be concerned with getting 1/4" to the foot pitch.



Edited 1 times.

Yes thank you for checking. I have maintained a 1/4" slope for vents and drains.

I get it now!!! A 2" vent is allowed to run 120' and only 1/3 can be horizontal. Which leads to the max of 40' horizontal. Thank you so much for putting this in to terms even I can understand.



Edited 1 times.

you need 1/8 or 1/4 pitch on drains depending on size and 'run'

you need sliiiggght pitch on vents

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

An 1/8" per foot of back slope would mean a ~5" elevation drop over 37'. Curious why not just add another roof vent rather than try to tie them all together in the attic? Typically fixtures that are somewhat close are grouped into a header for single exit, but if the kitchen is 37' away it usually makes more sense to add another roof vent. Put them low on the back side of the roof and they won't be seen from the street.

One does not need 1/8 pitch for a vent.

Vents need juuussst a 'hair' of back-pitch.

Juuust enough so that internal condensation does not 'puddle'.

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Well, the wife wants a cleaner look without extra or added vents. The roof is already on, and I am about to land the kitchen sink as I type this. Happy wife = Happy life. All fixtures are vented except kitchen and laundry room sink. The tub is a different story.

if allowed in your area use an automatic vent (studor vent)

packy ...... sheeeeez


the OP wants to do it as per good practice and you are recommending do it to MINIMUM !!!!!?

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



Edited 1 times.