| Question: 05-04 | Code Section: 7 | Date: | OBC 2006 Reference: |
Question: Where can a vent off the top of a sewage tank extend to or be connected to? Does this vent have a load? Are any of the following installations legal?
1. conveying the sewage tank vent independently to open air and increasing it to 3″.
2. extending the sewage tank vent to a 3″ stack vent and connecting to the stack vent independently.
3. after connecting the vent to the top of the sewage tank, connecting other vents in the location of the tank to the sewage tank vent and then connecting this vent to other venting systems in the building.
Interpretation: (On. Reg. 403/97) This vent can extend to open air or be connected to any other vent pipe in the vicinity. Vent terminals are found in Sentence 7.5.5.5.(1) and we all concur that all of your examples a) through c) comply with that requirement.
Some members, however, did express concerns with a) in that although it met the intent of the code, it could possibly cause hoar frost at the terminal point because there was not enough heat produced in the tank to keep the terminal open.
As for loading the sewage tank vent, the initial size of that vent is determined in Clauses 7.5.6.5.(1)(a) & (b) and until other vent pipes connect to it there is no load associated with the sewage tank vent.
Now once you connect the basement fixture vents to it and provided the connections to the vent comply with 7.5.5.4. the loading would only be restricted by 7.5.7.2. and Table 7.5.7.2.A.