Humidistat fans are often misunderstood. In essence, they are just like standard extractor fans, but with one clever feature: they can switch on automatically when humidity rises. Many users mistakenly describe them as unreliable or “faulty” due to nuisance triggering, or not triggering at all. But more often than not, problems arise from a misunderstanding of how they work and therefore not having been correctly set up.
A common misconception is that humidistat fans act as dehumidifiers, actively lowering humidity beyond that which a standard fan can achieve. In reality, the built-in sensor simply triggers the fan when moisture levels rise, making it ideal for bathrooms, kitchens, and utility rooms. This automatic operation means you don’t need to rely on the light switch to operate the fan, which is handy for en-suite visits in the middle of the night or utility rooms where dryers and laundry can spike humidity regardless of whether the room is in use.
Most humidistat fans allow you to adjust the trigger sensitivity. This isn’t about controlling the humidity to a precise level; it’s about tailoring the fan’s operation to local conditions. For instance, a home in a typically humid area may require a different setting than one in a drier region.
Environmental context matters. In the UK, ambient humidity can fluctuate dramatically. A humidistat set at 80% will generally perform well year-round, though coastal regions or properties with existing damp may need a slightly different approach where the ambient humidity is generally higher naturally. In the case of a house with existing damp issues, however, this is where a humidity-triggered fan can help to improve conditions, running when required to remove the unwanted moisture. It may mean a fan will extract more often to begin with, while it helps to remove the humidity, but it should hopefully settle once the dampness has been dealt with in the home. This could be within days, or it may take much longer to address the damp issue.
External factors, such as open windows or the temperature of incoming air, also influence performance. As your fan extracts air from your bathroom, new air is drawn into the room to replace it. Suppose you have an open window during a hot shower in a humid climate. In that case, the fan may run longer to reach the set level as the external air's humidity level may be higher than the percentage set as the trigger point on the fan, leading to a vicious circle of humid air replacing humid air. Whereas a closed window, maintaining a warmer room, can allow balance to be restored more quickly.
For properties with ongoing damp issues, a continuous-running dMEV fan with a humidistat is highly recommended, as it helps remove moisture continuously and will recondition a damp space far faster and more effectively than a standard intermittent fan.
In short, a humidistat extractor fan is a smart, low-maintenance way to manage moisture and protect your home, so long as it is installed and set up correctly. Understand how it works, adjust it for your environment, and it will quietly do its job, keeping your rooms fresher, drier and healthier.
For guidance on the best way to set up a humidistat fan, please see our article in the link below:
Understanding Humidistat Extractor Fans: How They Work and How to Set Them Up
Below is a selection of Humidistat fans recommended by our in-house experts: