The Importance of Air Intake Ventilation

Good air intake ventilation is very important in achieving the desired performance results from your Attic Breeze solar powered ventilation product.  Attic Breeze fans will operate at peak performance when supplied with the proper amount of ventilation.  However, failure to supply adequate air intake ventilation will result in decreased air flow and reduced cooling performance from your product.  We recommend becoming familiar with your attic ventilation design to ensure that the required amount of air intake ventilation is installed for your Attic Breeze solar powered ventilation system to operate at maximum efficiency.

How Much Intake Ventilation Do I Need?

The national building code recommends a minimum of one square foot net free area intake ventilation for every 300 CFM of powered ventilation air flow.  Since Attic Breeze solar powered fans are variable speed in terms of air flow, the calculation for required air intake ventilation must be made at the fan's highest rating to ensure adequate ventilation under the full range of operation.  The table below may be used to estimate the minimum required amount of air intake ventilation for all Attic Breeze solar powered ventilation products.

Minimum Required Net Free Area Intake Ventilation

When using any type of powered ventilation product for an attic application, all passive attic vents will become sources for air intake.  Unlike passive ventilation where air flow must travel from the lowest point in the attic to the highest, powered ventilation uses air intake from all areas of the attic both high and low.  If built to national building code standards, your home will have a minimum of one square foot net free area passive ventilation for every 300 square feet of attic space.  Estimates of total passive attic ventilation based national building code standards are shown in the table below.

Estimated Passive Attic Ventilation Based on National Building Code

What is Net Free Area?

Net free area is a term used to describe the amount of ventilation space available in any type of vent that may be used to freely pass air flow.  This is essentially the empty spaces you see in the installed screens and louvers on most passive vents.  As the screen mesh size decreases, net free area decreases as well and air flow through the vent becomes more difficult.  As a general rule, screen mesh sizes of ¼" mesh and larger have a negligible effect on net free area air intake ventilation.  The chart below shows the effect of screen size and obstructions on net free area for various types of soffit vent designs.

How Do I Add More Intake Ventilation?

In some cases, it may be necessary to add more air intake ventilation to meet the recommended requirements for installation of an Attic Breeze solar powered ventilation system.  This is accomplished by either adding soffit vents, gable/wall vents, or passive roofs vents.  The decision as to which type of vent to install should be based on proper balancing of airflow, as well as space availability.  The chart below gives the net free area ventilation for typical roof and gable passive vent sizes.

When adding additional air intake ventilation to your attic, install the new passive vents at least 10 feet away from the Attic Breeze solar powered fan.  More air intake ventilation is always better when working with active ventilation systems.  Attic Breeze recommends installing more than the minimum requirement if possible should you need to add additional ventilation.

My Home has Ridge Vents

When installing Attic Breeze products in conjunction with ridge vents, the solar attic fan unit should be installed a minimum of 5-7 feet away from the ridge vent to allow for balanced airflow through the attic.  Experience shows that this distance will typically allow enough air diffusion space for proper balancing of air intake ventilation from both the ridge vent and other passive roof vents installed on your home.

Please note that while the Attic Breeze solar attic fan is operating, the ridge vent will work in reverse acting as air intake vent.  In fact, every passive vent on your roof will act as an air intake vent while the fan is operating.  This is not a problem, just a different method of operation for your roof's ventilation system.  When the solar attic fan is not operational (at night, during rainstorms, etc...), the ridge vent will function as normal.

What about Attic Depressurization?

Attic depressurization occurs when there is not enough air intake ventilation to support the volume of air being removed from the attic.  While depressurization can occur naturally (i.e. the sudden cooling of your roof during a rainstorm), it may also occur when using powered ventilation products.  Since air flow follows the path of least resistance, for any powered ventilation system to create attic depressurization and pull conditioned air into the attic, it must have enough power to both overcome any air intake ventilation present, as well as produce enough power to overcome frictional effects created from pulling air through the small cracks and opens between the attic and living space of your home.  While this is an unlikely scenario for a home with properly installed air intake ventilation, attic depressurization can occur under the circumstances of poor attic ventilation and a powerful fan source.

Although by appearance they may seem the same, AC powered attic fans and Attic Breeze solar powered attic fans are distinctly different.  AC powered attic fans have a very large source of grid power from which to use, as well as a constant speed AC motor.  When an AC powered fan does not have enough "free" air intake ventilation to support the motor's operating speed, the fan simply uses more power in order to maintain motor speed, thus pulling more air from any air intake source available.  If the AC powered fan is not installed with enough attic air intake ventilation, attic depressurization may occur.

By contrast, Attic Breeze solar attic fans have both a limited source of solar power and use a variable speed DC motor.  Given the same situation, our solar attic fans are designed to reduce fan speed rather than promote attic depressurization because additional power is simply not available.  Additionally, Attic Breeze UltraFlō^® technology is engineered to minimize any chance of depressurization by design.  Best of all, our Breeze Mate™ control system eliminates the possibility of attic depressurization by putting ventilation control in your hands.  Breeze Mate™ allows you to test for attic depressurization and directly observe the performance of your Attic Breeze solar attic fan product.  With the Breeze Mate™ control system, you will never need to worry about attic depressurization again.