Plumbing vent: old galvanized to new PVC (amateur)

[Dan]

hi all, wondering if someone can give some advice to me (a home owner trying to improve a few things around the house; a complete amateur)

i am replacing galvanized steel piping in my 1940s home. for one 'run' of galvanized steel pipe, it connects into a cast iron stack. my thought is to cut the large run of galvanized pipe and replace with 2" pvc. the run of galvanized pipe that i am replacing is through a non-load bearing wall that will be covered up (i.e. framed, drywalled, and painted).

i need to get this done as quick as possible and dont want to mess with the cast iron stack to galvanized steel connection that may be fused/corroded together. i cut the large chunk of galvanized already and looks clean inside the galvanized pipe. i can access the cast iron stack and the galvanized <--> pvc connection to the iron stack even after the wall is finished.

the inner diameter of the galvanized pipe is 1.25" (outer is 1.75"). i can't find any no-hub coupling that will fit this 1.25" ID / 1.75" OD pipe. based on pvc dimensions charts (like this: https://formufit.com/pages/pvc-pipe-size-dimensions-chart) i will need a no-hub coupling that is sized as '1.25-inch to 2-inch' but can't find that anywhere!

my options seem to be:

(1) find coupling with one end that measures ~1.75-inch in inner diameter to accept galvanized pipe and the other fits a 2" pvc. finding coupling that fits 2" ID pvc is easy. the former seems unlikely

(2) replace the entire iron stack with pvc/abs

(3) use 'flexible' fernco coupling (instead of the no-hub) and fail inspection

are there any other options that i'm not considering?

 

[Jeff H Young]

It should be closer to 1.625 diametor 1 5/8 " Go with fernco like you said if it fails ask inspector for permission to proceed and youll call him back to inspect the stack when you complete in a few days. ( since you said its all acessable) Our inspectors have to check drywall nailing after its hung and befor tapeing any way so no extra trip out

 

[Sponsor]

 

[Reach4]

the inner diameter of the galvanized pipe is 1.25" (outer is 1.75"). i can't find any no-hub coupling that will fit this 1.25" ID / 1.75" OD pipe. based on pvc dimensions charts (like this

Do you have nominal 1-1/4" pipe, schedule 40 pipe which is 1.660 OD ?

Always secure your pipe above before cutting out the pipe below. A riser clamp can be useful for that.

So where is this pipe you are trying to connect to -- is that going through the ceiling?

 

[Dan]

It should be closer to 1.625 diametor 1 5/8 " Go with fernco like you said if it fails ask inspector for permission to proceed and youll call him back to inspect the stack when you complete in a few days. ( since you said its all acessable) Our inspectors have to check drywall nailing after its hung and befor tapeing any way so no extra trip out

yup, that's an option but i was hoping for a more permanent 'temporary' option. such as if i could find the 1 1/4" coupling now and wait till this winter or later to go back and remove the last bit of the galvanized steel connected to the iron stack and replace the galvanized with pvc.

Do you have nominal 1-1/4" pipe, schedule 40 pipe which is 1.660 OD ?

Always secure your pipe above before cutting out the pipe below. A riser clamp can be useful for that.

So where is this pipe you are trying to connect to -- is that going through the ceiling?

well as far as the dimensions of the pipe. i measured the pipe's outer diameter and it comes out to 1.74" (some decimal places after 1.74, but given it was with a string and low precision math: circumference = diameter * 3.14, i rounded up to 1.75)

the inner diameter, once i cut the galvanized pipe, i measured the inside and got the 1.25". could my measurements be off? is there not such thing as a 1.25" ID / 1.75" OD pipe?

i take it from your comment my description gave you the impression that the galvanized pipe is running 'vertically' (i.e. from floor to ceiling).

the galvanized pipe is running horizontally inside the length of a wall. this plumbing vent comes from a vertical sink galvanized pipe. this galvanized pipe connects to the cast iron stack.

see the photo above: this is not the room in the basement that i am talking about but this is very similar in that it is the same pipe material, dimensions (not length, though), and running horizontally into the same cast iron stack, but at a location further 'down' the iron stack

 

[Jeff H Young]

add 3/8 to the size of pipe inch and a quarter plus 3/8 equals 1 5/8 all day long if you cant find a coupling to fit I cant either. although 1 1/2 copper is that same od dont know if a shielded coupling is available that size

 

[Dan]

add 3/8 to the size of pipe inch and a quarter plus 3/8 equals 1 5/8 all day long if you cant find a coupling to fit I cant either. although 1 1/2 copper is that same od dont know if a shielded coupling is available that size

any thoughts on another solution? can i place a solid rubber or neoprene 'shim' around the pipe to make the galvanized pipe fit tight?

 

[wwhitney]

Most likely you've got the OD off a little and it's 1.66", standard for 1-1/4" Schedule 40 pipe. Try a Proflex 3001-215 to go from 1-1/4" Schedule 40 to 2" Schedule 40.

Cheers, Wayne

 

[Dan]

Most likely you've got the OD off a little and it's 1.66", standard for 1-1/4" Schedule 40 pipe. Try a Proflex 3001-215 to go from 1-1/4" Schedule 40 to 2" Schedule 40.

Cheers, Wayne

Thanks for the reference. Looks like I can order it online. I'll report back as soon as I get it and try to fit it.

 

[Jeff H Young]

I know its closer to 1.660 than 1.750 " So I wonder how a 2 inch vent is going to fly choked down to 1 1/4 " It seems as though a a2inch vent should remain 2 inch as it rises getting bigger if anything not reduce in size. But hope it flys its just temporary. 2 inch ip x 1 1/2 copper thatll work Thought he said he couldnt find the size? if not perfect its super close

 

[Dan]

I know its closer to 1.660 than 1.750 " So I wonder how a 2 inch vent is going to fly choked down to 1 1/4 " It seems as though a a2inch vent should remain 2 inch as it rises getting bigger if anything not reduce in size. But hope it flys its just temporary. 2 inch ip x 1 1/2 copper thatll work Thought he said he couldnt find the size? if not perfect its super close

yes! i found a fernco coupling, exactly as you said, fernco p3000-215 was the right product!

https://www.menards.com/main/plumbi...lexible-coupling/3000-215/p-1444430431820.htm