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26040 Ynez Road, Temecula, CA United States of America 1-888-QUIETCOOL Mon-Fri 8:00 AM - 5:00 PM PST Contact Us

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#1 cooling, energy savings, and ventilation system in Australia!

Whole House Fan Sizing Formula

Per square meter of floor space, we utilize a standard formula of 34m3/h, 43m3/h, or 51m3/h. A good system would have a flow rate of 34m3/h, a better system would have a flow rate of 43m3/h, and the best system would have a flow rate of 51m3/h. Use the calculator on this page to figure out how much airflow your home requires. This mathematical formula is applicable to homes of any size, with the caveat that more airflow is always preferable.

In case you forgot, the Energy Department, PG&E, and the California Energy Commission all back up our sizing formulas.

Considerations Regarding Size

The sizing of a whole-house fan system also requires attention to the following two factors:

Location: A good system should function well if situated in a cooler coastal zone. The optimal setup makes the most sense in a desert environment where daytime temperatures are high but drop significantly at night.

Ceiling Height: If the ceilings in the home are higher than 8 feet, the system should be sized somewhat larger to accommodate the additional air volume.

whole house fan locations

central whole house fan system

CENTRAL (SINGLE-FAN) SYSTEM

There is only one fan in a centrally mounted system, as the name suggests. A single system is often put in the middle of a single-story residence, or at the top of the stairs in a two-story home. While one QuietCool system will do a fine job of ventilating a whole house, zoned systems allow for more precise temperature regulation in specific rooms.

ZONED (MULTI-FAN) SYSTEM

The homeowner has complete control over the ventilation and cooling conditions in their home with a multi-fan zoned system. Rather than adding up the CFM of each fan in a zoned system, the total CFM output of all fans in the system must meet the system’s sizing requirements. When cooling the home, zoning fans can be activated together. More precise control over the airflow in separate rooms is possible with a zoned system.

zoned whole house fan system

ZONED (MULTI-FAN) SYSTEM

The homeowner has complete control over the ventilation and cooling conditions in their home with a multi-fan zoned system. Rather than adding up the CFM of each fan in a zoned system, the total CFM output of all fans in the system must meet the system’s sizing requirements. When cooling the home, zoning fans can be activated together. More precise control over the airflow in separate rooms is possible with a zoned system.

attic venting

HOW TO CALCULATE VENTING IN THE ATTIC

Once you determine the correct size of the system you need, based on the sizing principles we just discussed, you need to ensure there is adequate attic venting based on the total CFM of the system.

Attic venting is measured in square feet and is expressed in net free vent area.

As stated by the Department of Energy, PG&E, and the California Energy Commission, each home should have 1 square foot of net free vent area for every 750 CFM in the QuietCool system.

It is very easy to measure the venting in your attic. Simply measure the width and length, in inches, multiply them together; divide by 144, and that is your gross free vent area in square feet. Then, simply deduct 25% off that number to get the net free vent area, which accounts for any air restrictions through the vent. Do this for every vent, add them all up, and you will know exactly how much venting you have or will need to add to equal the venting requirement stated in your local building codes.

Power Venting

So you need to add more vents, right? Sometime that’s easy! Just add a gable and a few O’Hagans. But other times it can be very hard. We have a product that can fix a lack of venting.

Power venting is the process of putting an attic fan in the attic. When the QuietCool is turned on, the attic fan is turned on as well to help move air out of the attic faster.

We discovered this by accident while we were testing our fans in our HVI-916 testing booth. When we put an attic fan in our booth while testing the air flow of one of our ducted whole house fans, the attic fan increased the air flow of the whole house fan by over 25%.

We recommend using our attic fans to improve ventilation when you are 1 to 2 square feet short of the amount of ventilation that is needed.

We always recommend adding more venting when you don’t have at least 2 square feet of venting.

power venting

Power Venting

So you need to add more vents, right? Sometime that’s easy! Just add a gable and a few O’Hagans. But other times it can be very hard. We have a product that can fix a lack of venting.

Power venting is the process of putting an attic fan in the attic. When the QuietCool is turned on, the attic fan is turned on as well to help move air out of the attic faster.

We discovered this by accident while we were testing our fans in our HVI-916 testing booth. When we put an attic fan in our booth while testing the air flow of one of our ducted whole house fans, the attic fan increased the air flow of the whole house fan by over 25%.

We recommend using our attic fans to improve ventilation when you are 1 to 2 square feet short of the amount of ventilation that is needed.

We always recommend adding more venting when you don’t have at least 2 square feet of venting.

attic venting

VENTING TIPS AND TRICKS

If you’re still unsure whether you have enough venting, there are some simple tests you may perform after the whole house fan is installed.

Turn on your whole-house fan and place your hand over a switch or plug outlet to feel a very small quantity of air blowing through. If there is a lot of air coming through, this indicates that you are most likely under vented.

Another approach to check for inadequate ventilation is to open your attic access door and switch on your fan. The open attic access will allow your fan to vent more effectively, allowing you to witness how much more powerful your whole house fan becomes.

Remember that there will always be some air coming out of your light sockets, switches, and outlets. This is very normal. Even if you don’t have enough venting, your whole house fan will still work. It will simply be underperforming. For the best experience, we always recommend that customers install the appropriate quantity of venting.

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