Bathroom exhaust/extractor fan on batteries


I am planning a bathroom renovation and now it has ‘passive’ ventilation. There is a 12x17.5cm open vent goes into ventilation shaft that exhaust a couple floors above into the roof.
I would like to put in a fan that pulls the air out and ideally add some smarts too it however… there is an issue.
I do not have power in the shaft and no real way of wiring it up.

Are there any small battery powered fans?

I do not have a mold issue probably helped by heating rack in the bathroom but I would love to improve the situation.

You will not find a battery fan that will run more that a couple of times unless you buy something that was meant for a recreational vehicle and have a car battery charged by solar cells or something.

You will need to install an extractor fan tied to the power of the main ceiling light if you don’t run new wires, this will then use a duct to pipe into the vent that leads outside.

I have this fan installed in the bathroom with the power coming in from the ceiling light when its turned on:

and its using this duct to funnel the steam etc out through the vent leading outside that is just above the ceiling:

I use a zigbee based switch to control the on and off state based on the humidity detected via the switchbot hub 2.

I was thinking if I do not need a lot of it I could do by with batteries but I was concerned that may be an issue.
I may have to downgrade to just some small servo that actuates the vent shutters.

I am not planning on resurfacing the celling, so I can not carve a channel for a wire of my light into concrete ceiling and having a power wire dangle above shower also not an option.
Also I can not put in a duct because apartment below is using same shaft and it is has 15x12 cm cross section so it would effectively plug it with ducting.

I’ve seen a 12V computer fan work in a canal boat bathroom, but have to agree with SG that the energy required to move useful amounts of air is going to kill even a bank of 18650’s pretty quickly.

EDIT: Data point - my bathroom fan is rated 25W @ 230V, which were the power linear (it isn’t, but…), 25W/ 12V = over 2A! Even the best Noctua PC fan is going to pull quite a current from batteries.

Then your next option is to use a dehumidifier and have its pipe draining into an input where the sink is and just leave the window/passive out open when in use.

I have a small dehumidifier draining out into the same outpipe that my washing machine uses at my sink in my bathroom to keep it constantly draining so I don’t have to manually empty it. I have it also tied to the humidity in the bathroom and running when the exhaust fan runs for about an hour and is done removing the steam+a little extra humidity from the bathroom.

For dehumidifier I also have no power outlets in the bathroom, so I have nowhere to plug it in… though I may solve it. That depends if the old plans are not lying and there is an outlet behind some tiling. I also start running into space limitations…
What I think I will do is talk with my neighbors about installing something like wind powered ventilation shaft cowl on the roof. Maybe with solar option depending on the price.
Maybe some small actuation servo on battery and that would close the vent blinds so that in winter warm air does not get pulled out.

Yea work with your neighbors to get the best overall solution that works with both your setups to get the most out of it.

Does the bathroom have a window. Nothing as good as cracking open a window. A linear actuator on the window.

I’ve been tempted to do this myself for my window so I can have it automated to open when its not raining and close when it is but since its vertical slide and takes a little force to do so I would need a dual actuator setup most likely, something of a project to think about in the future heh.

edit for those interested

and for this type

Wormgear and a motor

Unfortunately there is no window in my bathroom, so it is not an option either. However the videos you showed are not a waste. I have a place where basement door is a hinge door that are very heavy, so I was planning on installing some “air springs” to ease the lift and I was thinking of adding some small actuator to be able to pop it up automatically… but that project is going to have to wait a couple of years lol :smiley:

The links to the vids was from TH3xR34P3R.