Filter Fan Plus

My Dad is the smartest man I know. He majored in Physics and graduated near the top of his class, in an era before laptops, graphing calculators, and the Internet. Even more amazing to me,

Backgrounds and textures: group of old slide rules, or slipsticks, retro science abstract

he did all his calculations using a slide rule (pictured left). I now have my Dad’s slide rule proudly on display in my office; it reminds me of my Dad and all the lessons he taught me. Today we rely on computers to do the heavy lifting when calculating heat transfer rates and other thermodynamic data. Thank goodness we don’t have to remember how to use a slide rule!

Here’s the key, though – whether using a slide rule or your iPad, there are fundamental principles that still must be respected, no matter how you get to the answer. In other words: how you get to the solution doesn’t matter. All that matters is that you make the right engineering decision. That choice needs to consider the system requirements AND the total system cost.

In terms of electronics thermal management, we need to challenge certain assumptions to design the most cost-effective solution that will protect your device from temperature extremes.

Changing the paradigm: Active vs. Passive Enclosure Cooling


Air conditioning is considered active cooling. Like in your home in the heat of summer, you simply set the temperature and the unit maintains it, just like you programmed. Simple right? Not so fast!

As humans, we like a specific temperature to function at our peak. The same applies to the electronics inside your enclosure. However, although air conditioning may work fine in your design, it might be overkill. Consider these factors:

Power requirements:

An air conditioner will require the most power compared to other (e.g., passive) technologies.


Active cooling solutions cost the most initially and on an ongoing / maintenance basis.

True system requirements:

 Many times, your electronics need only to be slightly cooled, not requiring a very tight window of control or not requiring a temperature significantly below ambient.

Condensation risk: 

Air conditioning removes humidity from the air, but that condensate has to go somewhere. So you’ll have to engineer some way to handle this thermal “waste stream.”

A filter fan may be a better choice. Filter fans are used to provide cooling via forced air circulation. The interior temperature of an enclosure can be reduced by channeling cooler, filtered outside air into the enclosure, and pushing hot air out of the enclosure. The resulting airflow prevents the formation of localized hot pockets and protects electronic components from overheating.

A filter fan can protect your enclosure from high-temperature exposure with:

  • Fewer power requirements.
  • Less cost to install and maintain. 
  • Less mess, with no troublesome condensate to be managed.

Our takeaway: don’t always assume you need to design an air conditioner for your electronics enclosure.

We can help you select the right thermal management solution. Contact us today for a consultation.

We get it. We’re in the thermal management business, and we’ve heard the jokes about fans versus air conditioners. Usually, it’s someone asking about, for example, getting in a vehicle on a hot Summer day in the South and instead of turning on the air conditioner… why not just crank up the fan instead (cue laugh track)? When it comes to controlling the environment inside an enclosure, it’s a similar question:

Aren’t you just replacing hot air with more hot air?

Geek humor! But seriously, we do get this question from enclosure designers, who want to know why they don’t just go ahead and design in an air conditioner. In this case, the temperature desired for a human body is much different than what is necessary to maintain the integrity of electrical and electronic components. So essentially, an A/C is overkill for most NEMA enclosures needing environmental control.

STEGO offers a wide variety of Filter Fans that provide a net cooling effect via forced air circulation. The interior temperature of an enclosure can be reduced by channeling cooler, filtered outside air into the enclosure, thus expelling hot inside air. The resulting airflow prevents the formation of localized hot pockets and protects electronic components from overheating.

So, no, our technology doesn’t just move hot air. Instead, it modulates the air inside the enclosure to a cooler state. This, in turn, enhances the longevity of the components inside and the working life of the overall enclosure. Furthermore, with the addition of new air-flap technology on the air outlet side, we have achieved an unparalleled high degree of airflow.

What’s the difference between FPI or the FPO system (FPI = “in”, FPO = “out”)?

This is another question our tech support teams get asked regularly.

There are two distinct filter fan options. The FPI system is the more commonly utilized installation system. A filter fan located in the lower part of the enclosure draws cleaner, cooler air into the enclosure (airflow direction “In”). This system consists of a filter fan and an exhaust filter.


With the newer FPO system, the filter fan will be located in the upper area of the enclosure to draw warmer air out of the enclosure (airflow direction “Out”). The FPO system consists of an intake filter and exhaust filter fan.

For a video explanation of how this all works, check out this link: STEGO Filter Fan Plus Animation

The answer to the title question is simple economics: it’s just not feasible to power, control, and manage an air conditioning unit inside most NEMA enclosures. Also, it’s overkill!

For more questions about thermal management, reach out to one of our experts.

Designing complex electronics that perform perfectly outdoors is, well, complex. At STEGO, we believe that protecting those complex projects from extreme climates should be the simplest part of your design. That’s why we use German engineering to create the highest quality thermal management components to protect your designs from anything Mother Nature throws at it. We’ve been pioneering Thermal Management for over 40 years now. With STEGO parts installed, you can rest easy that your complex design is reliably protected for the long haul.