I've noticed for the first time last night that water was pouring from the AC/Heat venting in the ceiling in the downstairs laundry room when my daughter was upstairs draining the water after taking a bath. Why do you think this happen? Could there be a leak in the shower upstairs causing water to leak in the vent downstairs?

I've noticed for the first time last nite that water was pouring from the AC/Heat venting in the ceiling in the downstairs laundry room when my daughter was upstairs draining the water after taking a bath. Why do you think this happen? could there be a leak in the shower upstairs causing water to leak in the vent downstairs?

Cut a square patch out of the ceiling directly under the tub drain. Take a wad of TP and start up next to the tubs drain wipe around. Tell me where you see moisture when you wipe around. Exactly what joint's leaking. Back to you, Tom

Definitely - leak from the tub somewhere and the water is just taking the path of least resistance to flow, which happens to be the vent.

If I contact a plumber will it be expensive? Should I get it fix now or can I wait for a later date. I will not let anyone use that bathroom.

fritolay : what is TP? Sorry I don't have a clue. Also when you state cut a square pathch out of the ceiling directly under tub drain. Where exactly is that? Once again no clue. I'mlady :) If I contact a plumber will it be expensive? Should I get it fix now or can I wait for a later date. I will not let anyone use that bathroom.
TP is toilet paper. Do you have access panel behind the tub? If so open it and use the TP b\lot around then drain and tell me where you pick up moisture.
No one can say what a plumber would charge until you know exactly where the leak is and how hard it is to get to.
Is you can localize the leak for me I might be able to save you the cost of calling in a plumber. Backn too you. Tom