Small vent

For gas appliances, why do the smaller exhaust vents need to be connected to the vent above the larger appliance connector? I am looking for a scientific explanation.

think in terms of draft and volume…

volume as in btu’s

He asked for scientific:p;-)

Well then he’s at the wrong forum. :mrgreen:

It’s so when they are both running the larger one passing by the smaller one will help the smaller unit draft. When they are reverse you can sometimes see venting problems with the smaller BTU unit. The smaller can be lower but the pipe size has to increase before the larger pipes connection.