DewStop™ – Condensation Sensing Fan Switch

The folks at DewStop™ sent us their FS-100 Fan Switch to review. In today’s tighter more energy efficient homes there’s a huge need for better ventilation and moisture control. We’ve written several articles on the causes of window condensation and the leading culprit is too much moisture in the house due to poor ventilation.

Make Your Fan A Smart Fan

There are lots of great bathroom fan timers on the market but none of them take it a step further like the DewStop™ Fan Switch. DewStop™ Fan Switch uses technology to monitor temperature, humidity and dew point, similar to what meteorologists use for weather prediction. This sensory software finds the room’s condensation level and prompts the fan to turn on or off.

DewStop™ Features

  • Fan turns off when condensation is no longer present on the walls
  • Saves energy
  • Low maintenance
  • Long product life
  • Use with your existing fan
  • Manual on/off control also included
  • Manual on/off light control included with the FS-200 model

DewStop™ Fan Switch Review

We recently installed the DewStop FS-100 in one of our bathrooms to test and evaluate the product. For this particular application it was installed in a bathroom with a tub/shower combination, a dedicated bathroom exhaust fan and a separate light that’s wired with the exhaust fan.

DewStop™ Installation

The DewStop™ Fan Switch is very easy to install if you’ve got some basic electrical experience. Installing this switch is very similar to most switches with the exception that a neutral lead must be available.

This is true for all electronic type timers and occasionally poses a problem for older homes that may only have a switch leg at the switch box. (Basically you can open the switch box and check for a neutral wire which will be white. The box must have at least one white conductor and two black or one red and one black.)

Before you begin it’s very important that you shut off the electrical breaker that suppliers power to the room. Then go ahead and remove the old fan switch and exposing the ground, neutral and two hot leads.

If you look at the back of the DewStop™ you’ll see four leads, Red = Fan, Black = Hot Feed, White = Neutral and Green = Ground. The DewStop™ switch comes with wire nuts and pre-stripped wires so there are no special tools needed. Just connect green to green, white to white, black to the hot feed and then red to the hot supply on the fan. Neatly push the wires back into the junction box and install the face plate.

Installation takes less than five minutes. The installation directions are easy to follow and understand. Overall the installation can be performed by most anyone with very basic DIY skills and basic knowledge of electrical work. If you don’t feel comfortable working with electrical switches be sure to consult an electrician. Electrical circuits can be VERY dangerous so it’s important that you consult a professional if you’re not sure what you’re doing.

DewStop™ Performance

As you can see in the photo above we tested the DewStop™ switch to see if it would automatically turn on as advertised. Well we’re happy to report that the switch turned on just as it’s supposed to when the bathroom filled up with moisture as you see above. Once the fan turned on it stayed on until the room was completely cleared out.

In addition to the automatic feature the DewStop™ can be turned on manually until you either manually turn it off or the 30 minute timer shuts it off. These features make the DewStop™ extremely versatile and much more advanced than simple timers.

Overall Impression

The DewStop™ Fan Switch works great. Having an automatic fan switch that senses humidity and dew levels is a huge advantage when trying to prevent mold and mildew in damp bathrooms. The fan switch is very easy to install and and control. Priced under $60 we think the DewStop™ is a great value and a product that home owners should consider for bathrooms, laundry rooms and even spa rooms.

Todd Fratzel

I'm full time builder for a large construction company in New Hampshire. I run their design-build division that specializes in custom homes, commercial design-build projects and sub-divisions. I'm also a licensed civil and structural engineer with extensive experience in civil and structural design and home construction. My hope is that I can share my experience in the home construction, home improvement and home renovation profession with other builders and home owners. I'm also the Editor-in-Chief and Founder of Tool Box Buzz. Please feel free to contact me if you have any questions, suggestions or you'd like to inquire about advertising on this site.

View Comments

  • Can I get a 3 way Dew stop switch? My bathroom has three way switches now and I want to replace the in the room switch and leave the regular 3 way on the outside of the room.


  • my original switch has 2 wires ,white and black oh and ground makes 3.
    there is no red wire . where do i connect the red wire on the DEW STOP SWITCH to ??

Recent Posts

Framing Stick Nailer vs Coil Nailer

Which is Better a Stick Nailer or Coil Nailer? Framers have many choices in nailers…

6 months ago

How Many Roofing Nails Per Square of Shingles

Estimating How Many Nails for a New Roof When it comes to estimating materials for…

6 months ago

Composite / PVC Decking – Layout Tips & Advice

Composite / PVC Decking Layout Tips and Advice Composite and PVC decking have really changed…

7 months ago

Benefits of an ERV System (Energy Recovery Ventilator)

Benefits of ERV Systems (Energy Recovery Ventilator) If you're building a new home or doing…

1 year ago

Vermiculite Attic Insulation Abatement

Vermiculite Attic Insulation If your home was built before 1990 there is a chance it…

1 year ago

Nuisance Tripping of AFCI (Arc Fault) Circuit Breakers

Arc Fault (AFCI) Circuit Breakers Tripping Often An arc-fault circuit interrupter (AFCI) or arc-fault detection…

2 years ago