How long can a bathroom exhaust fan be connected to an external duct?

To be honest, the exhaust fan in the bathroom is generally recommended to be no more than two meters of external pipes, if it is too long, then the effect of this low-power exhaust fan is basically not large.

The smell will not run into the bathroom, I don't believe it, a three-way connects the entire sewer, you think about it is impossible to have no smell, now the general bathroom rarely has windows, so only with a ventilation fan, plus a three-way is to link the entire sewer and your bathroom, there is no smell, the ghost believes.

There are no windows, only ventilation fans.

Both of these options are feasible, but comparatively speaking, I still recommend that you choose the first option, directly punching holes in the roof, which is the best, as for the waterproofing problem you mentioned, it is not a problem, as long as you use a professional punch machine to punch the round hole, the waterproofing will be easy to handle!

It can be connected to 50 centimeters to 1 meter, it is too long and the convulsion effect is not very good.

Absolutely.

According to the design requirements, the exhaust holes left for the bathroom when building the house are only connected indoors and outdoors, and the odor is discharged outdoors when there is odor. There is no legal clause that only the holes left by the construction boss can be drained, so you can drain them however you want. There is no legal clause that stipulates where the gas in the bathroom must be discharged, as long as it does not affect other people's lives, so you can discharge it anywhere.

However, the exhaust fan should be turned off in time after it is not in use, otherwise, the temperature of the motor will rise to a certain level after the long-term operation of the motor, which will lead to an accident.