Cool Off, A New Whole House Fan App!

We’ve often talked on this blog about how we are big promoters of “open” systems. That’s why we included an application programming interface in our 2nd Generation control package, and why we were very excited that a third party developer released an iOS app that works with our 2nd Gen. controls. It will come as no surprise, then, that we’re once again excited to share a new independent whole house fan app, Cool Off.

turn off ACCool Off helps homeowners get the most out of their whole house fans (both AirScape and other manufacturers) by automatically notifying them whenever the temperature outdoors drops below their desired indoor temperature. This, as I’m sure you’ve already figured out, allows you to know exactly when and when not to run your fan.

Unlike AirScape’s own Temperature Sensor Package, Cool Off doesn’t use an external temperature sensor to gauge the outdoor temperature. Instead, the homeowner enters their location into the app and it finds the temperature using readings from Weather Underground’s network of weather stations. Accessing this network has some great benefits:

Users can use both actual and “apparent” temperature settings, which is a very nice option in more humid climates. “Apparent” temperature readings take humidity into account in order to provide a measure of how hot it feels like outside, as opposed to what a thermometer says it is. Air feels increasingly hot as humidity rises—in a humid climate, air conditioning removes humidity from the indoor air, making it feel cooler than humid outdoor air even when it actually isn’t.

Furthermore, thanks to Weather Underground’s forecasting, Cool Off can estimate the time of day you’ll be able to switch from A/C to your whole house fan. This is subtly useful. If, for example, it is too hot to run the fan at the moment, but will be cool enough soon, you might want to turn off your A/C now, endure the heat for a short spell, and save a little money. Likewise, if it won’t be cool enough to run the fan until the early hours of the morning (which could easily be the case during a heat wave), you’ll want to know, so you can turn on your A/C early and not lose any sleep.

It is important to note Cool Off cannot directly control either our fans or those of any manufacturer. That said, we are very happy its developers have published it. Our new Digital Touch Controls, now shipping standard with every AirScape fan, are not compatible with our own Temperature Sensor Package, which can only be used the 2nd Gen. controls. If a homeowner would like to easily gauge the outdoor temperature, without upgrading their controls, Cool Off is an excellent way to do so.

To learn more about Cool Off, visit their website at If you check out their site, you’ll also learn that the app is available in versions for both iOS and Android operating systems, and will work on both smartphones and tablets in either ecosystem. You can download Cool Off on the App Store or Google Play.

New Controls!


This spring we are introducing several new models of whole house fans. We’ve made very large investments in R&D over the past couple years, but thus far have only adopted new innovations piecemeal. Collectively, these upgrades will boost our fans’ airflow at maximum speed by an average of 28%, and their efficiency by 37%. We’ll detail every improvement in a series of posts, but, to start, we want to discuss what will be the biggest change: a new control system.

In all of our new models, we will be replacing our 2nd Generation Controls with our new Digital Touch Controller. This new controller provides every fan with 10 speed settings (up from 7), and a 12-hour timer. Instead of traditional “buttons”, the touch controller use capacitive sensors to turn its face plate into a touch pad much like your tablet or smartphone. Simply touch your finger to the correct part of the face plate and, voilà, the fan responds accordingly. We’ve even added two banks of LEDs to display the fan’s current speed setting and the amount of time remaining on the timer. You can see this remarkable new controller in action by following this link.

So, beyond its cool technology dashing good looks, what are the benefits of the Digital Touch Controller? Several, actually:

Read more

The Power of Open Source

We’re big believers in the power of Open Source here at AirScape. We run as much of our business as we can on Linux workstations, and we’ve published the application programming interface (“API”) that controls our fans. Now, not everyone’s a programmer, so we’ve released our own apps for both iOS and Android devices on the App Store and Google Play. In our heart of hearts though, we’d love to see as many of our customers as possible take advantage of our open platform to configure a unique control system that works best for them.

Porchdog app for AirScape Fans
Porchdog app for AirScape Fans

This is why we’re excited to write about one of our customers who’s taken our API and built upon it. Scott is a software developer who bought one of our fans for his Bay Area home and “fell in love with it.” He decided to write his own app, which went live on the App Store yesterday. The “Porchdog app for AirScape Fans” includes all the same functionality as our own, with a different interface. A unique feature of the app is a series of notifications guiding the homeowner to turn their fan on or off based on conditions outdoors. Scott has also included a utility for estimating the outdoor temperature without needing to outfit your fan with one of our temperature sensor packages.

Now, since we didn’t develop this new app ourselves, we don’t provide support for it. If you need support, you’ll need to contact Scott directly; the support website is Also, the Porchdog app is only available for iOS devices.

We try to be the first to recognize one app doesn’t fit all, even when it comes to our own products, so we’re very excited one of our fans has built on our prior work to develop this new app. If you’re an iOS user and looking for an alternative to our own app, we’d encourage you to check out Scott’s.

Making Sense of Performance Claims

Skeptical Blog Fan Curves

As a bunch of engineers we love running tests. It brightens our day to finally find out if our ideas for better performance actually delivers the goods. A lot of the time we have to go back to the drawing board (or, nowadays, Solidworks),but some of the time things turn out pretty good. In fact, this winter we began construction a new test chamber. We’ve successfully exceeded the limits of our current chamber, and need to be able to accurately gauge much higher and much lower airflow (relative to our whole house fans) for some new designs and products we have in development.

Our sales team often fields calls from interested homeowners wondering why our fans are so much larger than our competitors’, which often promise equal or better performance. So we want to take a moment to offer our explanation for the this difference. Considering the time and energy we commit to R&D, it can be a little frustrating for us to be constantly explaining why, but our explanation is simple: Our fans are bigger because they have to be, physically, to deliver the performance we certify they do, and we’re skeptical, extremely skeptical, of other manufacturers’ performance claims.

Here’s why:

The performance of all fans is governed by a set of physics equations known as the “Affinity Laws”. These equations set out the relationship between a fan’s diameter, how fast it spins, how much airflow it produces, and at what power. There are three of these laws and they are:Fan Affinity Laws - CopyWith a little bit of algebra we can move the elements in these equations around to transform them into new equations, just as enlightening. The derivative equation we’re most interested in for our purposes here is below (we’ll let the p1/p2 term fall out of our equation from this point forward, as all of our performance specs are published as adjusted to a standard air density).Fan Law Derivative - CopyNow, we said above that we’re very skeptical of some of other manufacturers’ performance claims. The equation above is why. Consider, for example, our 5.0e fan. This fan is our most power and most efficient. At its highest speed, the 5.0e moves 5064.9 cubic feet of air per minute. Its motor draws 809.8 watts to accomplish this, giving it an efficiency of 6.25 cfm/watt. One of another manufacturer’s fan’s published specifications claim it moves 4816 cfm while drawing 477 watts (10.10 cfm/watt), which is fine as far as things go, except for the fact it uses only an 18.5″ diameter fan blade, while our 5.0e’s blade is 24″ diameter.

When see such differences in performance, our first instinct is to ask ourselves how we might be able to improve our own performance. For our 5.0e to achieve 10.10 cfm/watt efficiency on high, it would have to move the same 5064.9 cfm while drawing only 501.48 watts. This is a lot less than 809.8! We could improve our fan’s performance by changing the diameter of its fan blade, but what would the diameter need to be? Let’s do the math.Skeptical Blog Math 1 - CopyThe mathematics above show that, in order for our 5.0e fan to move 5064.9 cfm at the other fan’s 10.10 cfm/watt efficiency, the diameter of its blade would have to be 27.12 inches. That’s three inches larger than it is now! In fact, to simply just match the other fan’s 4816 cfm at 477 watts, the 5.0e’s blade would have to be 26.4 inches in diameter (our math is here). The diagram below visually depicts the difference between these for diameters.WebHow does a fan that is only 18.5″ in diameter achieve performance that would seem to require a 26.4″ diameter fan? Well, that’s why we are “extremely” skeptical of these performance claims. The fan affinity laws are laws of physics, they cannot be broken. Science is science to everybody.

So what would be the consequences if the other manufacturer’s performance claims were incorrect? Quite a lot actually. If we were to reduce our 5.0e’s fan diameter to 18.5 inches, it would require 1992.11 watts to move 4816 cfm. That’s over four times as much electricity the other manufacturer claims its fan uses to move the same amount of air. Translated into dollars and cents, this is the difference between a fan that costs 7.32¢ per hour to operate, and a fan which costs 30.56¢ to operate (at a cost of electricity of 15.34¢/kwh).

That’s a lot of money, considering a whole house fan is intended to be run for hours at a time on most (if not all) evenings during a large portion of the year. The graph below visually shows just how big this difference is.WebLikewise, if we were to reduce 5.0e’s diameter to 18.5 inches, 477 watts of power would only move 2988.29 cfm. That’s nearly 38% less than claimed! To meet the requirements of the State of California’s Energy Code (aka “Title 24”), a new house must have a whole house fan capable of exhausting 2 cfm per sq. foot of conditioned floor area in the home. The difference here is the difference between a fan that can be used to meet the code requirements for a house up to 2408 sq. ft., and a fan that can only be used to meet these requirements in a home up to 1494 sq. feet. If you installed this fan in your 2400 sq. ft. home—thinking it was capable of the greater airflow—not only would your home not be code-compliant, but your fan would be very ineffective. Such a low amount of airflow relative to the size of the home would do little to cool it.

New Test Chamber in Construction
Our new test chamber under construction

You can double-check our math for the above here and here. If you’d like, you can even come check out our new test chamber; our address is 625 Charles Way, Medford, Oregon. Until then, please enjoy a picture of it under construction.

At any rate, we hope this blog has helps you to understand why our fans are so much larger than other manufacturers’: they simply have to be to produce the airflows they do. And this is the same reason why we are so skeptical of those other manufacturers’ performance claims: they simply don’t seem to add up. We’d encourage you to be similarly skeptical, and to consider one of our fans for cooling your home this summer. If you find the mathematics above even a tiny bit confusing, please contact us. We’d be happy to walk through the numbers with you, and we’d love the opportunity to discuss the many other advantages AirScape whole house fans offer over other available brands.

Vertical Damper Installation, Part 2: Kohilo Fans

In a prior post we covered how to install our AirScape line of whole house fans vertically or on a slope. In this post, we’ll do the same for our Kohilo line.

There are many differences between our AirScape and Kohilo fans, but the important one for our purposes here is how their backdraft dampers function. AirScape fans use actuators to mechanically open and close their damper doors whenever the fan is turned on and off. This allows us to insulate the dampers and for their door to seal airtight when closed.

Read more

Coming Soon to Southern California: Rolling Blackouts

Every summer has its own story. For residents of Southern California, this summer’s story is going to include a chapter about rolling blackouts. The L.A. Times wrote the prequel earlier this month. To summarize, the natural gas leak this winter at the Aliso Canyon Underground Storage Facility has left Southern California short on natural gas, which means that, come summer, the region’s utilities could be unable to generate enough electricity to meet demand. To prevent the entire grid from, power managers will institute rolling blackouts by cutting electricity to certain individual sectors of the grid at moments of peak demand.

To many, the possibility of a blackout seems quaint. Who doesn’t enjoy the occasional candlelit dinner? And what parent doesn’t wish their kids would watch less television? The reality of blackouts, however, is deadly serious. Electricity provides us with more than just entertainment. We depend on it to, among other things, refrigerate our food, power hospital equipment, and illuminate traffic signals. We hardly notice it when it’s there, but without electricity are lives are much less safe.

Read more