Whole House Fans vs. Attic Ventilators

What is the difference between a Whole House Fan and an Attic Ventilator? First of all the Whole House Fan is mounted in the attic, while an Attic Ventilator is mounted on the roof or the gable wall of an attic.

The Whole House Fan pulls in cool outside air when you open the windows at night and exhausts the stale, hot air out. It is a natural source of fresh air that saves energy. Because a WHF operates between 2000 CFM and 6000 CFM they quickly exhaust hot indoor air and bring in the cool outside air.

An Attic Ventilator’s purpose is to get hot air out of your attic and bring cool air in. However, it can be pulling that cool air from your house. The fan can depressurize the attic by exhausting air from it, as well. Replacement air comes in either from the outside intake vents or from openings/cracks into the house. The main reason to cool an attic is if you store things in it or have ductwork or HVAC equipment up there. If this is the case, your HVAC equipment and ductwork would better serve you in the interior of your home somewhere, or the insulation should be moved from the attic floor to the sloped roofing of your house.

As you can see the Whole House Fan is designed to cool your home and save you energy while the Attic Ventilator, while good in theory, can actually pull cool air from your home and in turn cost you more in energy.

Designing the 5.0e

5.0e, Front
5.0e, Front

Our newest model of whole house fan, the 5.0e, is has been available on our website since spring. We’re extremely excited about it. Not only is this our first new fan in several years, but it is also our most powerful and our most efficient fan ever. Moreover, we’re manufacturing a greater portion of this fan “in-house” at our Medford, Oregon facility than any of our other fans. We’re also seeking a patent for some of the innovations behind its performance. As our patent is finally “pending”, we can now share the story of the 5.0e’s development.

Read more

4.5 Installation – Maximize Airflow, Minimize Noise

Recently we have been using our new and improved sound testing chamber to make sound comparison videos of our different models. The shooting of these videos reminded us that the set up of the ducted models will make a significant difference in the CFM and noise levels. Basically, improper installation will decrease the unit CFM and increase the amount of noise. Some numbers for comparison:

AirScape 4.5 improper installation –  high 59 dBA / low 50 dBA

AirScape 4.5 proper installation –  high 55 dBA /low 46 dBA ……A 4 dBA difference!

The photo above shows the correct install dimensions for the 4.5 WHF. You will notice that we have a nice even bend and the ductwork is fully extended (Note that we used an extra length of the provided chain to help support the bend). It is important to maintain the 20″ diameter of the duct through the 90 degree bend. This will ensure that you get unrestricted airflow through the duct and will help disrupt the sound waves. You also want to make sure the duct and fan are fully extended from the 90 degree bend. This moves the fan to the furthest point from the grill opening, thus decreasing the decibel level.

Airscape 2.5/2.5e installation: The install dimensions for the AirScape 2.5/2.5e are very similar. The duct should be 21″ from the attic floor. It should extend 44″ from the 90 degree bend to the fan (you may be able to extend it to 48″ if the bend is supported as shown in the photo above). The top of the fan should be 44″ from the attic floor.

Changing Fan Speed Settings on Your AirScape 2.5e

2.5e Control Board v3.0Not only does the AirScape 2.5e have phenomenally low energy use, the user can also select up to 5 different CFM settings. The 2.5e fan motor has inputs which we program at different CFM. From the factory it is set for a low speed of 1512 CFM at 42 watts and a high speed of 2536 CFM at 196 watts. Now let’s say that the factory low speed setting does not provide enough airflow to properly cool your home over night. The fan speed settings can easily be adjusted for more airflow. For example, you could change the low speed from 1512 CFM to 2080 CFM. At the same time you could also adjust the high speed setting so that the fan will move 2604 CFM on high (see example #2). This is as simple as moving the low and high speed wires on the 2.5e fan control board (located on the fan housing) to different connections. The fan speed adjustment is described below:

  1. Turn your 2.5 e off. Unplug the fan power cord and turn off power to the damper box by unplugging it or switching the circuit breaker off if hardwired.
  2. Remove the fan junction box cover (located on the fan housing).
  3. Move the low and high speed wires to different taps to adjust fan speed (see photos).
  4. Plug in the fan power cord and turn the damper box power back on.
  5. The unit is now ready to operate at the new CFM settings.


TP1 1512 43
TP2 2080 108
TP3 2536 197
TP4 2604 216
TP5 2778 258

What is a cubic foot and a CFM?

balloonOK, first the boring defintion. A CFM stands for cubic foot per minute. This term is used as a measurement of airflow rate for ventilation systems. The cubic foot refers to a (mythical) cube of air 1 foot x 1 foot x 1 foot. CFM becomes a flow rate since we measure how many cubic feet are flowing by per minute.

Now, let’s get some perspective on what a cubic foot and CFM represent:

  • It takes about13.5 cubic feet of air to weigh one pound. A 2,000 square foot house will contain 16,000 cubic feet of air. The weight of all that air is only 1,185 pounds.
  • Warming or cooling air is “low calorie”. To warm all that air in your house up from 50 degrees F to 70 degrees F takes about 5,688 BTU’s . The smallest house furnace puts out 40,000 BTU’s per hour. So how come it takes so long to heat up the house on a cold morning?
  • An unsealed door jamb, leaking 50 CFM would over the course of 24 hours, leak out 72,000 cubic feet of air – not “low calorie”