Why Your Bathroom Still Feels Damp Even With the Fan On

One of the most moist and humid places in a house is the bathroom. From hot showers to running water from the sink, and a lack of ventilation, the humidity stays in the bathroom long after the water is turned off. Over time, this moisture settles on the walls, mirrors, ceilings, and grout, creating an optimal environment for mold and mildew to start to develop.

Most homes use simple ventilation fans to combat the humidity in their bathrooms. However, these types of fans are only as good as the people using them.


A new line of smart switches is looking to combat this problem by using the condensation to automatically turn on the fan. One such switch is the DewStop FS-300-W6, a moisture switch designed to turn on bathroom fans when condensation starts to develop.

Why Bathrooms Trap Moisture

According to the guidelines of the ventilation experts at the HVAC Insider, as well as the product literature of DewStop, the formation of condensation results when the air comes into contact with the dew point temperature at which the water vapor turns into liquid form.

Once the process of condensation is established, the surfaces remain damp for longer periods of time, thus providing the right conditions for the formation of molds as well as damaging the surfaces.

The traditional ventilation fans operate by removing the moist air from the surfaces. The operation of the traditional ventilation fans is effective only if the fan is operated at the right time and for the right duration. If the fan is operated too late or too early, the moisture may already have formed on the surfaces of the bathroom.

The DewStop switch tries to solve this problem with its use of moisture-sensing technology that tracks condensation levels, not general humidity. According to product details provided on the official website of DewStop, as well as on product documentation provided by TremTech, QUE moisture sensing technology is used to identify when condensation actually begins to form on bathroom surfaces.

Key Features of the Smart Switch

The switch fits into a standard single-gang wall switch configuration, which allows the user to install the device in place of an existing fan switch without extensive modifications to the existing electrical configuration.

According to the documentation provided by TremTech on the operation of the device, the switch is compatible with standard 120-volt household power supplies and most permanently installed bathroom ventilation fans.

The device has a countdown timer that users can set to control the length of operation of the fan. The user can set the timer to run the fan from five minutes to sixty minutes, depending on the specific needs of the bathroom.

A blue LED indicator provides a clear visual signal showing when the fan is operating. The switch also includes manual on and off control so that users can run the fan whenever they prefer.

It appears that the installation requirements for this product are relatively simple for homeowners who have some familiarity with basic electrical installation. The switch appears to be designed for installation in wall boxes that are common in most residences and can be wired directly into the most common types of copper wire that are often utilized in the construction of homes.

Documentation provided for this product in most retail stores from the manufacturer TremTech indicates that the switch can be utilized in conjunction with nearly any permanently wired 120-volt bathroom fan that homeowners might have in their residences.

How It Compares With Other Moisture Sensors

There are several other manufacturers of humidity sensing fan controls. For example, the Lutron XactSense switch and the Panasonic WhisperControl Condensation Sensor Plus are other products that attempt to automate the ventilation of the bathroom.

A review published by Fine Homebuilding points out the following: "Many humidity sensing switches actually measure the overall humidity level, not the level of condensation. This can cause the fan to come on too soon or stay on too long.".

Automated ventilation can also reduce energy consumption. Bathroom fans draw electricity whenever they operate, and extended runtimes increase household power use.

According to product documentation published by DewStop, operating fans only when condensation appears reduces unnecessary usage and can extend the lifespan of fan motors by minimizing mechanical wear.

A Small Device With Practical Impact

One would not necessarily think of bathroom ventilation as a significant technological problem, but the issue of controlling indoor moisture levels is a problem in many residences.

Smart switches to sense the presence of condensation offer a basic solution to a problem where a homeowner may forget or incorrectly estimate the need to run the fan.