Sound Reduction part 1 – Duct Board

Your AirScape is already the quietest whole house fan on the market, but there are a few install techniques to make it even quieter. We’ve decided to dedicate a few blog entries to some techniques that will help with sound reduction.

We’ll start with a simple installation step that works with all AirScape models. You can easily line the inside of the framed opening (between the unit and grille) with duct board. Duct board is a resin bonded fiberglass board that has acoustic and insulative properties. The fibrous mat surface of the duct board helps absorb sound and allows for the smooth passage of air. The fiberglass body of this material usually has an insulation value of R-4. The duct board can easily be installed in new or existing installations using either adhesive or screws and flat washers. In fact, we love this material so much we lined one wall of our new office with it (our lead engineer’s rants on energy efficiency, life, and politics are a little more muffled now).

Duct board resources:


Installation for attics with loose fill insulation

Loose Fill Insulation

We often get asked if AirScape whole house fans can be installed in attics with loose fill insulation. The answer is yes, with one additional install step. The idea is to stop the insulation from being displaced by the air movement generated by the AirScape. We now offer a breathable synthetic fabric that can be placed on top of the insulation to stop any displacement. The installation is as simple as laying the material down in the attic where the fan discharges and tacking or weighting it down. The final step would be to turn the AirScape on and adjust the fabric material as needed.

The Loose Fill Insulation Cover (LFIC) is available in 9’x10′ sheets and can be found on any of the product pages on the website.

4.4e/4.5 Install: Low Attic Clearance

Often a WHF will not easily install in the traditional horizontal position. In some instances trusses or other obstructions will interfere with a normal installation. More often there is not enough clearance between the attic floor and the roof. One solution is to create a plenum box which the WHF will attach to. The plenum box can easily be constructed out of plywood and 2×4’s.  The red line in the photos represents the plenum box constructed for an AirScape 4.4e installation. The flexible ductwork and fan can then be mounted straight off of the damper box (the ductwork may have to angle slightly upward so that the fan does not touch the attic floor). A 90 degree bend in the ductwork is not necessary for sound attenuation in this application.

Installation Notes:

– Line the inside of the box with a layer of sheetrock to maintain any required fire ratings

– Use a sound attenuating duct liner for maximum sound reduction

– Seal all framing joints with latex caulk to make the box air tight

– Insulate the outside of the box to minimize heat loss

– Support any sags in the ductwork with additional chain

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.