I have a 2nd floor bathroom with no external ventilation. The house is a back split, however, without great expense and even then I am not sure it could be done, there is no way to install a ceiling ventilation fan. The gables are too low for a person to get near the ceiling of the bathroom and the inside walls are in-accessible Is a side wall installation is possible. The outside wall at the end of the bathroom has a 2 ft wide window in the middle and 2 ft on each side of the window. This wall could accommodate a fan but this is on an outside wall with normal wall 4-6" thickness. The outside idea might work but would require a vertical fan installation. Is this possible, this presents many questions, but my concern is the opening in the side of the house with regards to rain prevention and outside elements. I have asked but locally but no one seem too sure of what to do
Answer:
Your idea of a surface mounted fan is great and it can be vented to the exterior through the wall because the wall plate can be properly sealed. I would mount the fan in a separate box against one wall and then vent it by building a chase for the duct. This will ensure good ventilation and at the same time, permit you to deal only with what you add instead of dismantling what is already there except for leading power to the unit.
