I have 4 vents coming out backside of my roof ( span of approx 25' )


I plan to put metal roof and would like to combine the vents in attic
and just have one vent through roof.


Three vents are for my 2 bathrooms and one vent for the central unit.
One is a 4" ... the others are 1 1/2 " to 2".


I can show diagram of layout if needed.


Will it affect there operation by combining them in attic ?


Any advice appreciated.

It is OK to combine all PLUMBING vents into your existing 4" (plumbing) stock vent. Use long 90 degree bends to make the vertical-to-horizontal transition, and run 2" and 1 1/2" pipes up-slope with 1/4" per foot up-slope towards the point of connection. Use Fernco couplings to connect new and old. Secure horizontal runs with proper support so they don't collapse.

If your 4" main stock vent is cast iron, you have to support the pipe prior to cutting it. Cast Iron pipe is very heavy and it will collapse on you if not supported. Also cutting 4" cast iron is a bit tricky and you want to make sure you have proper tools, and "know-how-to" before you undertake such project. You will most likely need a second set of hands to help you with this project.

Not sure what do you mean by "... for central unit ..." but must stress - ONLY plumbing vents can be combined. Any other vent - as is air discharge vent, furnace vent, sewer ejector vent, dryer vent, kitchen hood vent, etc - cannot be combined in any combination and has to run through the roof independently

Hope that helps

Milo

I wanted to get in the attic to make sure I was giving you accurate info.

Here is the layout. All pipe sizes are outer dimensions.

Thanks for the reply.

All plumbing vents to be connected to the 3 3/4" vent (on the left). The A/C coil (.. I assume you meant to say furnace.. ) will have to vent separately. Therefore, you will end up with 2 roof penetrations

Thanks Milo... appreciate your advice.