The previous owners decided to cheap out and leave our suite bathroom with passive ventilation. There doesn't appear to be any wiring either, so adding a circuit would cost a lot of money and is a down-the-road problem. In the mean time I was wondering if a small fan would make any noticeable difference when the room fogs up. I have a 120mm PC case fan, smart plug, and battery-powered air quality monitor that detects humidity. Was thinking of rigging these three things together to create a short-term solution. But before I put any effort into it, I was wondering if this would even work? Thank you.
Bathrooms are required by the International Residential Code (IRC) to either have an operable window or an exhaust fan.
If you have a window, use it! That is the easiest solution. If the ventilation from just opening the window doesn't get rid of humidity/odors fast enough, or if the heat in the summer or cold in the winter is a problem, put a fan in the window. Sort of like a room air conditioner, but much smaller and a lot less energy. Based on comments, no window, but leaving this in because it could help others in similar situations.
An exhaust fan does not need a lot of power. A quick search shows plenty in the 20W - 30W range. So there should be no problem whatsoever piggybacking one onto your existing lighting circuit. You do not need a new circuit. There are two things you need for an exhaust fan:
This is the easy part. Easiest is to either replace an existing ceiling light fixture or splice into the wires (all splices must be inside a junction box, normally with wire nuts inside either the light fixture or fan) and mount near the existing light fixture. The catch is that this will usually require having the fan on whenever the light is on.
The better method is to run a separate cable from a switch to the fan, or a cable with two separate switched hots for light and fan from a double-switch. These possibilities are not that hard to do, but do require more work than a simple "fan/light in place of light with existing switch" setup.
- Venting of the Exhausted Air
This is usually the hard part. Since you don't have a window, you need to run ductwork either up to the roof (easy if this is the top regular floor and you have an accessible attic) or sideways (i.e., over other rooms and out the side of the house). Do NOT vent into an attic or inter-floor space - you will pay for it later with damage from the humidity.