Tub fills faster than open drain can handle?

[Vdawg]

New home prior to closing -- Part of the punch list was that filling the tub with the drain stopper open (the stopper is one of those lift-and-turn types) causes water to back up in the tub. That is, with the tub spigot running fully open and the drain open, the tub doesn't drain as fast as it fills. Running it like this for several minutes, the water starts to fill the tub even though the drain is open. Turning off the water allows the tub to drain. It's not a super fast drain, but it does drain at what appears to be a reasonable rate (hard for me to gauge if it's a "normal" drain speed).

Plumber told field manager that this is normal -- the drain can't take as much water as what enters the tub using the spigot. Using the shower head, the tub does not back up while in use with the drain open, at least in a short 3 or 4 minute run test.

Ran water on full in other sinks and it does not back up and they drain quickly, so I believe the main line is clear. Toilets flush normally.

Is this true? Is it normal for a tub spout to fill a tub faster than the drain can handle? Or perhaps just with this type of stopper; does it add such restriction as to make this type of behavior expected?

Thanks!

 

[Hightechburrito]

The tub spout has a much greater flow rate than the shower or sink faucets. Probably like 7-10 gpm vs 1-1.5 gpm.

Does the stopper come completely out of the drain? It may be a tight gap when it's just lifted that doesn't allow it to keep up with the supply.

 

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[Vdawg]

Thanks. I did remove the stopper and it filled a bit more slowly, but the drain still wasn't able to keep up and the tub (slowly) began to fill; although more slowly than it was filling with the stopper in place but lifted.

 

[Hightechburrito]

I'm not a plumber, so I can't really comment on whether the drain should be able to keep up with the supply, but it makes sense that a tub spout doesn't have any flow restriction, so the drain may not be able to keep up. How often are you running the tub without closing the stopper?

It's also possible that the water falls from the spout in just the right place around the drain and disturbs the water enough that it doesn't drain nicely. If you were to divert the water from the spout away from the drain does it change anything?

Is there a screen, or hair catcher, or anything like that integrated into the drain? That would reduce the drains flowrate as well.

If you really wanted to get into this you could figure out your supply's flowrate (fill up a 5gal bucket and time it), then mark the sides of the tub as it fills, then time how long it takes to drain.