Extractor fan control advice

I have a new requirement for which I'm not yet sure of the solution, and have not yet bought ANY compoents so would appreciate any advice which can be provided. In summary here is what I need:

We have a brick & concrete garage which is separate from our house, and I am trying to reduce the humidity/damp which means I need to install an extractor fan to create movement of air throughout. I would like to be able to trigger or the fan using automation (maybe with humidity or motion sensors, not decided yet, but certainly timers/schedule).

Due to the location any automation would have to be Zigbee - z-wave does not extend that far. I am assuming that I will install a standard extractor fan (like a bathroom) which would give local control and the run-on timer.

To ask a simple question; is there a zigbee module I can use alongside the lighting wiring which would also trigger the fan to come on (I guess if I wire it like a light it would then either stay on, or carry on with the run-on timer when switched off)?

Are there any recommendations for the actual FAN to go with this setup?

Thanks in advance


My initial reaction was that you are really looking for a dehumidifier. A fan would help if: 1) moisture is originating from inside the garage; and 2) outside humidity is typically much lower.

When I think "extractor fan", I think of the wall-mounted, industrial louvre fans (like this). Not sure how much air that you need to move or where you can exhaust - roof, wall, eves?

1 Like

@Hatallica brings up a good point in that a fan would only help if moisture is originating from inside the garage AND the outside humidity is much lower.

Since you are located in England I believe the outside humidity would be the cause of dampness in the garage. Therefore I don't believe a fan would be of much help.

@Hatallica's suggestion to install a dehumdiifer would probably be your best solution. They do make portable stand-alone dehumdiifers that you could plug into an electrical outlet. Assuming there is no floor drain to pipe to, you would have to empty the drain container occasionally or frequently depending on usage. The other option to handle the condensate is to add a small condensate pump and pump the condensate outside.

That is a fair response. I should explain better. We bought the house in September, and have discovered damp in the garage. So far we have 1. fixed the roof - was allowing seepage through the concrete roof leading to high humidity & damp, 2. replace. we have yet to seal the concrete floor - this is not damp sealed and hence rising damp coming up into the room. We have been advised to enable air flow to reduce the static humidity and allow the damp to clear, but will also be tanking the floor and walls to reduce the incoming damp.

I do have a freestanding dehumidifier which we are using to solve the immediate, but that is not a long term solution, and a simple fan will resolve most of the issues in the long term alongside the other work we are doing.

I should also note that our planned usage of the garage is storage, sometimes working on the cars, but mainly will be the "pain cave" with exercise bikes and other Gym equipment in use.

Hopefully that clarifies the request for advice on controlling a simple fan.

Also a good question, I will need to do some air volume calculations and come back to you. The installation & exhaust will have to be through a wall for practical reasons.

A 2-car garage with 9' ceiling is roughly 5,000 cubic feet. In theory, a 100CFM bath fan would cycle the air in under an hour, but ratings are very optimistic. My gut feel (take it for what that is worth) would be 250CFM for a 1-car and 500CFM for a 2-car. You can get single speed version with a wiring kit to plug into a standard outlet. Then, a cheap outlet such as Sonoff would be the only control needed.

1 Like

Thank you, that's about what I worked out (although for me it's 90 cubic.m. garage 5m x 6m x 3m). I am currently working my way through all the options of extractor fans and finding few which will do the air flow I'd like.
500 CFM is approx. 845 m3/h and most of the "normal" fans I've looked at are rated at 75 m3/h or something close (example: Vent-Axia Silhouette 100T 4"/100mm Extractor Fan c/w Timer | Vent Axia (454056B)) and that is at max. Think I'm going to need to look at something a little more industrial...

Fans are a series of trade-offs. A fan with lower flow may simply need to be run all-day. Typical bath fans use inexpensive sub-fractional HP motors and bearings that wear out quickly. After 100 hours of run time, noise increases and efficiency decreases.

It sounds like this may just be a stop-gap measure until the walls and floor are treated, which may help to alleviate some of the dampness. In which case, maybe running a smaller fan 24/7 is a manageable situation ... though that would eliminate the need for controls (booooo!).

I'm out of my comfort zone here but wouldn't a fan in or near the ceiling extract the air that has warmed (relative to the air at floor level)? It would seem you would like to keep that air and somehow extract air at floor level.

Extractor will be at (near) ceiling level.

I may have found a fan capable of moving enough air for me without being crazy noisy: https://www.screwfix.com/p/manrose-wf150a-commercial-axial-kitchen-extractor-fan-white-220-240v/89323

Now I've found and acquired the extractor fan I need some advice in relation to the controller.

I need a Zigbee module which will play nice with my hub, and provides ON/OFF control for the fan. I will have neutral wires present in the wiring and this does not need to be positioned behind a switch or anything like that.

Can someone recommend a suitable module?

Note: UK based.

Can you give an idea as to what the connections are like? I looked at the Manrose site and came away confused.

For starters, though, would something like the Sonoff ZBMini work? I recall someone from the UK reporting that they were able to get these. Ratings are OK. CE certified ... for what that is worth.

You mention Zigbee but have you considered Z-Wave 700 devices... they see to be coming on the market now. I am not sure about the radio licensing in the UK as to whether they are available there or not.

I just use the inexpensive Sonoff devices to detect humidity and a standard Z-Wave switch to control the fan.

SONOFF SNZB-02 ZigBee Mini Indoor Temperature and Humidity Sensor for Checking the Room Climate, SONOFF ZigBee Bridge Required, Indoor Thermometer Hygrometer with Alert, Works with Alexa, Google Home

I have a second Rule to turn it off.

on the Fan I have 3 terminals, Live, Neutral and Earth. the power must be switched on the Live, and does not support variable speed (so no dimmer controls).

I have z-wave in the house but have real issues with range due to thickness of the walls. The garage is too far away to get any device to pair (have confirmed with a Gen7 device).

In principle yes, but needs to be a zigbee device - am looking for a recommendation for the switch module.

The Sonoff temperature / humidity sensors are Zigbee!

Any Zigbee "mains" switch that works with Hubitat will do.

Is that the essence of your inquiry?

You are just looking for a UK-compatible Zigbee "mains" switch?

In my master bathroom, I have a humidity sensor. If the humidity sensor in there is more than 10% higher than the humidity sensor on the thermostat (which is outside the bathroom), it turns on the fan. You could do something similar...

If the humidity outside is lower than the humidity inside, turn on the fan.

You should also figure out where the moisture is coming from. It might require sealing of the block wall with paint specifically made for sealing moisture out of concrete or something like siloxane. Don't use regular paint, it won't work.

Can you run into an attic or similar and just use a basic ZigBee outlet? The IKEA Tradri ones are £10

Unfortunately not - this is going into a garage with a concrete flat roof. I have for now purchased a simple zigbee switch module and will see how well it works.

Ah cool, out of curiosity, what product did you buy and from where. I'm always a bit nervous about cheap 240v electronics so looking for a few pointers👍

I went to Vesternet and bought this switch module:

Much like you I am nervous about the no-brand modules on Amazon and E-bay and do not want problems with anything wired into my house. I do much of the electrics myself, and in this case the circuit is dedicated to the fan, and will have breaker and RCD protection at the fuse board but I am still cautious.

Download the Hubitat app