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# Venting Question

Member Posts: 113
I'm trying to calculate how much venting I need. If 3 mains share 11 feet of 4 inch pipe coming up from the header before splitting up, can I

divide the amount of air in that shared part of the mains by 3 so each of

the vents at the end of the 3 mains help vent the air out?

The total cubic feet of air in that shared part of the

main would be .99 cubic feet. If each main needs to vent the air on its

own I would need 1 Gorton #2 (1.1 cfm each) on each of the mains in the

back to vent the air at one ounce of pressure. If they all contribute

to the venting I would only need 1 Gorton#1 (.33 cfm each adding up to the .99 all together) on each back main.

What is suggested in the case of a shared main? Thanks.

• Member Posts: 1,567
it would seem reasonable

this question in one form or another has come up before without a satisfactory answer AFAIK .. it would seem reasonable to suggest that you can vent the main from the branches .. i might be better if you vented the 11' main as it's own entity and then vented the branches as their own entities... bottom line, as long as you give the air a quick escape route whether by 1 "stairwell" or several .. and as long as the venting of the mains is happening before the venting of the rads... you should be OK .. you never want to make the easiest way out to be by way of the rads.

Of course I'm open to any corrections.
1-pipe Homeowner - Queens, NYC

NEW: SlantFin Intrepid TR-30 + Tankless + Riello 40-F5 @ 0.85gph | OLD: Fitzgibbons 402 boiler + Beckett "SR" Oil Gun @ 1.75gph

installed: | gortons on all rads | 1pc G#2 + 1pc G#1 on each of 2 mains