Originally Posted by dpreznik
last winter I noticed lot of condensation in my insulation in my attic craul space. And now I am trying to reduce it. I suspect the wet air from at least one of the showers has not enough time to be removed by the fan.
You may have more of a problem than humidity from one shower. In fact, the shower may not even be the problem. The best thing I can suggest is do a search in these forums and elsewhere on the Internet about attic ventilation, attic insulation, and humidity. You most likely have a problem with high humidity in general in the house during the winter coupled along with inadequate attic ventilation and a leaky ceiling. The moisture in the house air gets into the attic where it condenses on a cold surface. That cold surface is probably the top of the insulation. Before you spend time and money redoing your bathroom fan study your attic ventilation situation first.
On the other hand, 19 feet is a fairly long run for a duct. Make sure the fan you already have is pushing air like it should. Make sure the duct is clear all the way and that whatever back draft damper is in there isn't stuck shut. You may just need to replace the current fan with a bit bigger one. It's location in the bathroom shouldn't matter much at all. I don't think fan location is your problem.