Net Free Air Calculator for calculating the airflow of a octagonal louver gable, roof or attic vent
This calculator will calculate the approximate net free air for Onyx Xteriors louvered vents.
These calculations are specific to our vents due to louver face size and louver spacing of other vent brands may differ.
How to calculate the net free area of a stop sign or 8 sided louvered vent?
1 inch deep: The calculation of our octagon louver vents without customization is apx width x height and divide by 2 for a 1 inch deep vent. Then 75% of that is the net free area.
2 inch deep: This calculates as width x height and divide by 2.5 and deduct this total from the original total of the width x height. Now use 75% of that total.
3.5 inch deep: Again, width x height then divide by 3. Now, deduct that number from the width x height total. And 75 percent of that will be the net free.
5.5 inch deep: Same, width time height and divide by 3.5 equals. And, deduct this sum from the width x height sum. Finally, 75 percent of that is the net free air area.
These calculations are for only the open vent area. Not including the flange or faced trim.
The octagon vents have a 1 inch face trim. Also, the first louver height total and the last will reduce the vented height measure.
These complete calculations are in the net free air calculator above.
Any variations or customization will slightly alter the net free air calculation.
Tip to tip vs opening size...the depth of the vent outside the listed depths...and any other custom variations.
Order a Octagon Louver Vent
All louver vents are manufactured with the 4-fold louvers locking onto a rail for extended life and strength of the vent. No facing or exposed pop rivets to pop out. Louvers stand straight and true.
Measuring is easier than most think.
All that is needed is the width and the height.
How to Measure
"Opening size" just means the measures were of the hole in the wall. For this, we will reduce your measures 1/4 inch dimensionally to ensure a good fit. Do not deduct measures yourself. They will not be accurate.
"Tip to tip" is if the vent size itself is to be the measures ordered with no reductions.
A "boxed base" is squared and boxed for a wall install.
The "roof pitch angle base" is in reference to the vent sitting directly onto the roof metal or shingles. For this, type the pitch into the comments box and we will pre-set the base at that angle.
The depth of the vent is as shown in the changing pictures. So, just how thick the vent will be or how far it will protrude into the gable wall.
Offering all 4 mounting styles.
If the rectangular vent will be painted or is matching a painted home color, enter primed white into the "color" box. Otherwise, enter the trim coil manufacturer and the color name and the finish.
Aluminum screen for the back of the vent is a bug screen for crawling and flying insects.
The grasshoppers and wasps can chew through the fiberglass screen.
The non vented has a solid metal back to block all air and water so it is decorative only.
And the wire mesh option automatically comes with aluminum screen to provide both bug and larger 4 legged critter protection (squirrels, raccoons, roof rats).
Shipping small products will be via UPS Ground or UPS Oversize Ground in wooden crates to ensure the product safety during shipping.
Larger aluminum products ship with SAIA Freight. These too are packaged in wooden crates. Freight items require a commercial delivery address or will be delivered to the nearest freight hub for individual pick up. Residential delivery is not available to all addresses.
If any product ordered is over 48 inches, call 901.281.2887 to find out if it will ship ground or freight.
Most items ship within 3 weeks. But due to some current shipping delays, always order products a month or more in advance to ensure delivery before needed. Stocking many of the commonly ordered colors speeds up the lead time drastically, but not on all.