Mary,

Venting interior moisture to the exterior is indeed the best practice.

Going through the roof or through the gable end wall are both fine.

Personally, I prefer exiting through the gable end wall as I prefer as few roof penetrations as possible.

Duct length can be a factor in regards to effective air movement, so it's best to minimize the length of dict as well as the number of turns.

Venting through the soffit is low on the priority list, for with today's houses having soffit-to-ridge venting, I've been told that the moisture can be drawn back in through the soffit vent.

Best, Mongo

In your case---with the possibility of a second bat visit---vent to the outside.

The present construction---ridge vent with soffit vents with the fan exhaust terminating near the ridge vent is the only way an in attic bath vent should be done. As evidenced by the lack of any problem.

However, shortening the exhaust line as much as possible is always a good idea---and then there is that pesky bat thing.

Mary,

Handymac's advice leads me to bring up one more point.

People who post on the forum are, obviously from varying geographic locations.

As such, we build under different codes and regulations. You mention that you have no specific code that you fall under.

I'm in CT and fall under the IRC. For a bit of guidance, the IRC 303.3 states:

Code Requirement:
* Minimum ventilation for the bathroom is to be a window of at least 3 sq. ft. of which 50% is operable, or a mechanical ventilation system of at least 50 cubic feet per minute (cfm) ducted to the outside.
(IRC R 303.3)

There are always state and local amendments or variances to a national code, but in a heating environment, which I'm in, I wouldn't intentionally vent warm moist air into an attic space. I've seen too many wintertime cases of it condensing on the cool underside of the attic sheathing or on the exposed shingle nail points, then dripping down.

Much depends on the age, air tightness, and climate that the house is in, as well as the amount of moisture being generated, the effectiveness of the fan in evacuating it, and physical size of the attic in comparison to the amount of moisture being vented.

In the end, for me it simply comes down to code. IRC requires bath vent fans to be vented to the outside.

Best, Mongo

That has definitely been a problem for us Mongo, living in N Illinois. There is staining of the ceiling next to the exhaust fan and water actully drips through the fan and hits the toilet seat below (had to stop blaming DH when I realized that!)

Should the exhaust piping be insulated to further minimize the possibility of condensation dripping down?

If you're going straight up through the roof it wouldn't hurt.

If you end up running horizintal to go out a gable end wall, have the horizontal pitch down slightly so condensate runs out the exit instead of bacl to the fan.

Since you're changing the duct, consider going over to 4" metal duct as well. Seal the seams with a roll of aluminum metal tape, available at HD and other box stores.

Metal duct with Al tape is not terribly expensive and it is a much more durable and air tight installation. Especially for horizontal runs where you don;t want sagging and pooling condensate.

Mongo