Can anyone tell me the equivelent length of a 3" PVC short and long 90 on a 90% furnace exaust vent.

I am being asked to lengthen the pipe by 7' and add 1 / 90 on the exterior of the house because it is dumping out next to a new hot tub.

The max length of the run can be 70'.

There is 31' of pipe 2 / 90s and 1 / 45 right now.

Thanks