It would be possible, we personally don't do it because our dps is shite, but I don't see a problem as long as your dps aren't braindead.
I have a feeling people in this thread is talking about 10m, while OP is talking 25m.
Shaman since Vanilla. All the way !
On normal you can easily three heal it. I don't see why you would though. On heroic, unless the DPS are great and decked out in heroic gear.