When choosing an extractor fan for a bathroom, one of the most effective and increasingly popular options is a model that includes a humidistat. These fans feature an integrated sensor that monitors moisture levels in the air and automatically activates the fan when humidity exceeds a specified threshold.
What Is a Humidistat Fan and Why Use One?
The concept is simple yet smart: air naturally contains water vapour, and factors such as temperature, climate, and indoor activity can affect how much moisture is present at any given time. In bathrooms, the most significant contributor to humidity is typically the shower. When hot water flows from a showerhead, it creates fine droplets that fall through the air, providing an ideal environment for evaporation. This causes a sharp rise in humidity within the room.
A humidistat fan is designed to detect this rise in moisture and respond accordingly. Once the air’s humidity reaches a preset level - usually adjustable between 60% and 90% - the fan will automatically start, helping to extract the moist air and prevent condensation, mould growth, and damp-related issues.
Adjusting the Humidity Settings
So, how do you decide what level to set your humidistat at during installation?
First, it’s important to understand that when these fans are first powered on, they often run continuously for a short period. This is completely normal and allows the sensor to calibrate itself to the environment. Because of this initial calibration phase, it's recommended to begin with the least sensitive setting.
Here’s where it can get slightly counter-intuitive: on fans equipped with a rotary dial to adjust sensitivity, turning the dial clockwise typically reduces sensitivity (i.e., the fan is triggered by higher humidity levels), whereas turning it anti-clockwise increases the sensitivity. Always refer to the manufacturer’s instructions if you’re unsure; this information should be clearly outlined in the user manual.
After the initial calibration period, which ends when the fan switches off for the first time, you can begin fine-tuning the sensitivity.
How to Set the Fan for Shower Use
To configure the fan to respond specifically to humidity generated by a shower or hot bath, follow these steps:
- Adjust the humidity sensor sensitivity to the least sensitive setting.
- Simulate a humid environment by running hot water in the bath or shower to elevate the room’s humidity.
- Gradually adjust the sensitivity: For dial-based fans, slowly turn the dial anti-clockwise in small increments until the fan activates. For units with dip switch settings, lower the trigger point one step at a time.
- After each adjustment, allow a good 10-20 seconds for the sensor to react before making further changes.
- When the fan kicks into operation, it should mean that your unit is now set up correctly.
This method ensures that the fan will only activate in response to significant humidity spikes, such as those caused by bathing, and not due to natural variations in ambient humidity resulting from seasonal weather changes or temperature fluctuations.
There are some exemptions to these adjustment instructions. For example, the Monsoon DMEVR100HT and Envirovent Silent Dual units have an intelligent humidistat that doesn't require any manual set-up and the Silent Tornado ST100DMEVHT has a digital interface that allows for precise manual calibration, which also can tell you the ambient level in your room to help you set up the unit to minimise ambient nuisance triggering.
Final Touches: Setting the Overrun Timer
Once your humidity trigger is configured correctly, you may also want to set the overrun timer, which controls how long the fan continues to run after it’s been triggered. At first, it’s advisable to keep the overrun setting on the minimum value to minimise the variables changing the fan operation during set-up of the humidity sensor. This can be adjusted later based on personal preference or specific room conditions, but we recommend a good 15 minutes of over-run for a room with a bath or a shower present.
Summary
Humidistat fans offer a hands-free, energy-efficient way to manage bathroom ventilation. By automatically detecting high moisture levels and responding only when necessary, they provide excellent protection against condensation and mould without the need for manual control. With proper setup, allowing for calibration and careful sensitivity adjustment, your fan will only operate when it’s truly needed, ensuring both comfort and efficiency.
Below is a selection of what we consider the best-in-class bathroom fans with Humidistats: