Air Flow Sizing Recommendations

How to size your WHF

We are often asked what kind of results can be expected when using a Whole House Fan, and/or what size fan should someone get based on their house size. The truth is, there are a bunch of factors to consider and no one size fits all answer – read on for things to consider when shopping for an AirScape Whole House Fan.

  • Climate – Do you live in an arid or humid climate? High elevation where it cools off quickly or a lower elevation where the heat stays longer into the night? Humid climates need more airflow to feel cool, and won’t cool down as quickly at night.
  • House size – Square Footage X Ceiling Height – How much volume of air needs to get moved through the house? High ceilings add a lot of air to the house that takes longer to move out of the structure so you want to take that into account in your airflow calculation.
  • Insulation level/tightness of the house – Good insulation will take the house longer to heat up, but once the materials are warm, it takes a lot longer to cool down. Good insulation will need to be cooled nightly or will have trouble releasing the heat. If the attic/walls/ insulation/etc. are still warm in the morning, the house will heat up again once the fan is off. If you have very little insulation, you will be able to cool your house quickly, but it will heat up quickly the following day. The best combination is a lot of insulation with a well vented attic and a whole house fan, so the structure can be properly cooled every night.
  • Personal comfort level – Do you live in a warm climate and rely heavily on A/C throughout the warm season? Do you currently sleep with windows open even if it is warmer than ideal outside for the fresh air, or because it cools off throughout the night? These 2 styles will need much different airflow in order to be happy with the results.
  • Personal security – Are you comfortable opening a few windows throughout the night or only before going to bed and after you are up in the morning? Ideally you want to run the fan as long and as low as possible. All night is best to really pull out all the stored heat from the structure. If you can’t do that, you’ll want a lot more airflow to feel the cooler air faster when you can run it.

Every house and micro-climate is different, and you know yours better than anyone. Once you know what to keep in mind, you can calculate your house volume and look at the recommendations for airflow:

Air Flow Recommendation Ranges*

First, calculate the volume of air in your house.
SQ ft x Avg Ceiling Height = approx volume of air in the house (ex: 1500sf x 8 = 12000cf)

Then, divide that by the cfm of the fan to get the time it takes to complete 1 full air exchange.
(ex: 12000cf / 1700 cfm = 7min air exchanges on high speed of 1700 WHF)

Or, divide it by the desired airflow (see below) to find out the cfm needed to achieve results.
(ex: 12000cf / 5 min = 2400cfm)

Here are the ranges I have found to be effective assuming your home has adequate insulation and is relatively airtight to store the cool air from the previous night through the next day:

3-4min = “Pull the hat off your head.” Moves air fast enough to dry the skin in a humid climate.

4-6min = Eliminate A/C in a dry climate – moves air fast enough to simulate the 68-70 degree consistent climate produced by A/C in a moderate, arid climate.

6-8min = Great airflow, esp. for the West Coast. You will not be able to run the fan until after it cools off in the evening, but it should only take 2-3 air exchanges to notice a nice drop in temperature and be comfortable. You can usually still feel a slight breeze depending on how many windows you open and if outside temp is significantly cooler than indoor temp (10 degrees). This is the minimum airflow we generally recommend.

8-10min = Slower air exchanges, but still moves the air fast enough to cool the structure (assuming the outside air is cool). Likely you will not physically feel this air moving over your skin. This can be adequate airflow in mild climates and well sealed houses. Not recommended for people who currently rely heavily on A/C.

10-12min = Usually this can keep ahead of the heat radiating out of the structure, but it will take a while to cool down in the evening and you will not feel any type of breeze or draft over your skin. This is really the bare minimum for airflow. The fan will need to run all night to see efficient cooling. Usually only recommended for people without A/C in mild climates.

AirScape WHF airflows on their highest speed*:
1700 LiftLock / Ventura = 1696 cfm / 1545 cfm
2500 Liftlock/LL Ducted = 2698 cfm / 2276 cfm
3200 Sierra / Ventura = 3253 cfm / 3132 cfm
3400 Sierra / Ventura = 3440 cfm / 3342 cfm
5300 Sierra / Ventura = 3253 cfm / 3132 cfm

*Ideally, choose a fan that has a high speed more than you think you need, so you can use it on the middle speeds, which are more efficient, but you can add air if you want or need to. Our fans all have 10 speeds, so finding one with a middle speed that fits your goals gives you lots of room to handle heat waves and hotter days.

Last, remember to check to make sure you have enough ATTIC VENTING. If you don’t, it is much better to add attic venting than to get a smaller fan.

More questions? Give us a call at 866.448.4187.

We’re happy to talk about your specific needs to find the best Whole House Fan for you.

Vertical Damper Installation, Part 1: AirScape Models

Over the years ve’ve also fielded a lot of questions from customers wanting to know if our fans’ dampers can be installed vertically (i.e. in a wall rather than over a ceiling) or at an angle on top of a vaulted ceiling. The short answer to both questions is “yes”, but there are some important limits that need to be considered, which we’d like to go over. Please note: this blog post is limited to our line of AirScape fans—Kohilo models will be covered in a future post.

Read more

Check Out this Great Video

As you may have heard, we are currently running a promotion offering rebates to customers who send us a video of themselves installing or operating their fan. You can read more about that promotion here, but you should also check out this video that was recently submitted by one of our customers—we’re really excited to share it because it was so well done.

And the video wasn’t the only thing well done. We often field questions as to how our fans’ dampers can be installed in a vertical orientation, or how to organize the installation in an attic with low clearance. This customer did a great job of both. Also, you’ll notice that this customer used many of our fans’ available accessories: the Openable, Washable Grille; an Acoustic Plenum; Wireless Remote; SafeSpeed Kit; and our Data Monitoring Package.

While we can’t identify them here, we’d like to thank our customer for sending us that great video. We’re looking forward to sharing more as the promotion continues.

Send Us Your Videos, Get a Rebate!


Note:  2015 Rebate ended.

When we’re designing our whole house fans, we here at AirScape endeavor to make them as easy as possible to install. Over the years, this effort has led us to create damper boxes that fit easily on 16″ or 24″ on-center framing, “plug & play” controls that use  low-voltage CAT-5 wiring, and a new latching mechanism for attaching ductwork to our new 5.0e. Our goal is simple: we want do-it-yourselfers to feel confident in installing AirScape fans themselves.

We often hear back from customers once they’ve finished installing their fans. Customers with unique installations often want to share their experience, and many customers simply want to share their pride in their own installation and excitement about our fans. We loving hearing back and getting feedback (both good and bad) from our customers. We’d love our customers to share more—we’d even like to offer a rebate to those who do.

Read more

How to Install and Program an AirScape LCF Remote Control


1. Plug the remote antenna into the control board 4-pin connection

2. Program the remote transmitter by cycling the power to the WHF off and on (unplugging and plugging in the power cord) or by pressing remote reset button

– A red LED on the control board will begin to flash indicating that the control board is ready to mate with your remote transmitter

– Press any button on the hand held transmitter

– The red LED will blink off

– Your WHF is now ready to use

3. Repeat this process to program additional remote transmitters

TOP 5 – Common Installation Errors

(1) Forgetting your attic gets hot in the summer – Buy and install your unit in the fall, winter, or spring when your attic isn’t 150 degrees

(2) Wiring wall switch to auxiliary actuator terminal – Doing so will blow the AirScape circuit breaker and possibly damage the control board. Check out our blog “Correctly Wire Your Wall Switch

(3) Switching the 110v power – So the AirScape plugs into an outlet …why not have that on a switch? First of all, doing so will not turn your unit on and off. All you will be doing is providing power to the actuator(s) and control board. By switching this power off you are eliminating the effect of having an automatic motorized damper door. This will cause you to lose the airtight seal that the closed door(s) create (one reason an AirScape is an AirScape) and allow conditioned air to escape to the attic.

(4) Installing the wall switch up side down – If the writing stamped on the metal is upside down, so is your switch.

(5) Installing the unit so the junction box is difficult to access – The more difficult it is to access your control board, the more challenging it will be to wire your wall switch.