# Ontario Circuit Venting



## billy_awesome (Dec 19, 2011)

Hey everyone, apprentice here.

My Boss is an old school plumber/old code/was taught code so long ago he forgets stuff and calls me.

I haven't been to school for circuit venting yet, he had a question on sizing his circuit and relief vents.

I would imagine the circuit vent minimum size would be the biggest trap, for this case 3" trap = 1 1/2" circuit vent. Now looking at the code book I saw that relief vents can be one size smaller than the circuit vent with a maximum of 2 inch, etc etc.

Now for sizing the vent I know that fixture units and distance come in to play with 7.5.8.3 (I think) thats the chart)

Would I add up all the fixture units in the circuit vented group (ie. 3 floor drains and a slop sink = 12 FU)? And would I calculate distance from the circuit vent itself? that would make sense.

Someone steer me in the proper direction? Ontario plumbers only please


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## MarkToo (Dec 17, 2011)

You got it. 

Sized based on hydraulic load. Distance measured from most distant connection (connection between two most upstream fixtures). 

Table 7.5.8.3.


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## billy_awesome (Dec 19, 2011)

MarkToo said:


> You got it.
> 
> Sized based on hydraulic load. Distance measured from most distant connection (connection between two most upstream fixtures).
> 
> Table 7.5.8.3.


distance to the trap? could you expand a bit more on two most upstream fixtures


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## MarkToo (Dec 17, 2011)

For sizing purposes, you measure the length of your circuit vent from it's most upstream connection which is between the two most upstream fixtures.

Combine the length and hydraulic load for sizing from chart 7.5.8.3.


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## The real E.P. (Aug 9, 2011)

Circuit vent is sized based on size of largest trap served in circuit vented branch, d.l.( the connection to the circuit vented branch to a stack vent, vent stack, header or open air), and hydraulic load of circuit vented fixtures


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