My bathroom has a single switch for the lights and fan. It is an ordinary, standard construction bathroom in a house built in 2007 or so, with sheetrock walls and a tile floor. The bathroom is entirely on the interior of the house (no windows).
I like to take showers in the dark, especially in the morning. I just find it a more pleasant way to wake up than stepping into a bathroom lit up like an operating theatre. Obviously, this means I’m taking showers without the fan running. I do take fairly hot showers, maybe 10-15 minutes long.
When I’m done, I turn on the lights/fan, and open the door to the rest of the house.
I live in Colorado - the air is usually fairly dry and the indoor humidity in the rest of the house is maybe 40-45%. The house has a good A/C system that I run regularly.
Am I risking any damage by doing this: rot, mold, etc.?
You are increasing the amount of moisture in the absorbent materials in the bathroom, and probably you have water condensing in various places and dripping. Some of the bigger problems may be hidden behind walls or under a vanity. However, unless you have some huge fan in that bathroom it’s not rapidly increasing the rate of what will happen eventually anyway.
If you live alone and generally take one shower per day that’s not excessively long - usually allowing the bathroom 24 hours before the next shower - you’re probably okay. The key, for mold especially, is any moisture or condensation built up on anything to dry completely each day or between uses.
If you’re like me - with a family of four, a tiny bathroom with the only shower in the house, with a wife who often showers twice per day because she exercises in the afternoon, then that fan probably needs to be on.
You can also swap your light switch out for a timer so that you can leave the fan running after you’re finished in the bathroom for some extra fan time that will turn itself off. I know you said the lights are on the same switch, but you can still use the timer for it - manually twisting the timer off after you’re finished with non-shower related bathroom uses.
You might try leaving the bathroom door and/or window open when you take showers like this. That will spread the humidity out and should result in less condensation, with or without a fan.
Otherwise, I don’t see it as a guaranteed problem, but it’s the kind of problem that is very particular about your exact situation (like number of people using the bathroom and where water condenses). Any problems can remain hidden for a long time before you discover the full extent of the problem. For me, I’d probably settle with leaving the door open a crack since it doesn’t require rewiring the bathroom.
As another precautionary measure, it might not be a bad idea to stick one of those dehumidifying jars in your bathroom. DampRid is an example brand name of what I’m thinking about. This would be a small extra step to help reduce any lingering humidity, though it’ll obviously be insufficient to prevent condensation during a shower.
A dimmer will cause problems with the fan, as they’re on the same switch.
A separate switch will require a separate wire to be run.
Get a timer switch. I have one for a single switched fan/light and it has six buttons for different durations and one button to turn it on or off. Take the shower in the dark, press the 30 min button, go about your life. The fan and light will run for 30 min and shut off.
Watch out for timer switches on a fan - that’s a motor, and they draw current differently than a bulb. Probably not a problem with the tiny motor in the fan; it would be an issue for the HVAC blower under the furnace.
Another LOUD voice for separate switches.
This isn’t (usually) a problem in a Master bed/bath suite, but: the switch near the door is the light; the fan is away from the door. Reason: when toilet training a kid, you want then to be able to see without the (potentially) scary fan noise. Never thought of that, did you dopers?
I actually bought a copy of the standard building code (back when I was messing with load-bearing walls, adding a bathroom, replacing/adding wiring. etc).
The requirement was for EITHER:
An openable window (actually any section of exterior wall of sufficient size)
A mechanical exhaust fan.
So, modify your bet - how many (professionally built) bathrooms had neither?
An old-fashioned window which had both top and bottom panes openable would beat the tacky exhaust fans.
The room which ended up as the master bath originally had an openable skylight. It was a constant leak of warm air, so I caulked the glass and covered the open/close bits. Code told me the room (which used to be the tub/lavy part of a split bathroom) now needed a fan. It got one. 2 switches, second is the fan, just like the hall bath.