Free duct static pressure calculator for dust collection
How much static pressure does your dust collection system need?
Every foot of duct, every elbow and every filter makes your fan work harder. Add up your longest run to see the static pressure and the fan it takes.
Updated by Höcker North America. Loss factors from the ACGIH Industrial Ventilation manual.
Dust collection static pressure calculator
With your normal gates open. Don't know it? The CFM calculator works it out from your machines.
Now add up your longest run: the machine farthest from the collector, or the one with the most bends.
Filled in for you. Change either one to match your collector.
Höcker fans run on variable speed drives, so they slow down as gates close and you only pay for the air you use.
Planning estimate for one run at standard air, galvanized duct. See the math.
Quick answer
How do I calculate duct static pressure for a dust collection system? Add up every loss along your longest run: the machine hood, duct friction, flex hose, elbows, the branch entry, the main duct and the collector's filters. Each loss is a factor times velocity pressure, which is (air speed ÷ 4,005)². At 4,500 feet per minute, 100 ft of 6 in duct loses about 5.4 in. wg (inches of water gauge, also written in. WC for water column) and one standard elbow about 0.3 in. wg.
What you get, free
Your static pressure report, line by line
Every loss listed
Hood, duct, flex hose, elbows, branch entry, main and filters, each in in. wg.
Air speed check
Whether your branch and main move air fast enough to keep chips from settling.
Fan size
Brake horsepower and the motor size it takes to pull your airflow.
A free layout check
Ask our team to look over your duct runs and gates.
How static pressure works
Where your fan's pressure goes
Worked example
One 6 in branch on a 6,000 CFM system
A 785 CFM machine on 30 ft of 6 in duct and 6 ft of flex hose, with two 90° elbows and one 45°, joining a 16 in main through a 45° wye. The main runs 100 ft with two 90° elbows to the collector.
Step 1: air speed and velocity pressure
Branch: 785 CFM ÷ 0.19635 sq ft = 3,998 ft/min, so VP = (3,998 ÷ 4,005)² = 0.996 in. wg. Main: 6,000 CFM ÷ 1.3963 sq ft = 4,297 ft/min, so VP = (4,297 ÷ 4,005)² = 1.151 in. wg.
Step 2: add up the losses
| Loss | Math | in. wg |
|---|---|---|
| Machine hood | 1.93 × 0.996 | 1.92 |
| Branch duct, 30 ft of 6 in | 0.04318 × 30 × 0.996 | 1.29 |
| Flex hose, 6 ft | 3 × 0.04318 × 6 × 0.996 | 0.77 |
| Branch elbows, two 90° and one 45° | (0.48 + 0.12) × 0.996 | 0.60 |
| 45° wye into the main | 0.28 × 0.996 | 0.28 |
| Machine branch | 4.86 | |
| Main duct, 100 ft of 16 in | 0.01292 × 100 × 1.151 | 1.49 |
| Main elbows, two 90° | 0.48 × 1.151 | 0.55 |
| Speeding up into the main | 1.151 − 0.996 | 0.16 |
| Main duct | 2.20 | |
| Collector and filters | default | 4.00 |
total static pressure. The fan needs 6,000 × 11.1 ÷ (6,356 × 0.65) = about 16.1 brake horsepower, so a 20 HP motor. These are the calculator's starting numbers, so you can follow along above.
Only the longest run counts
Air takes every path to the fan at once, so the fan has to beat the hardest one. Size it for the machine farthest away or with the most bends, and the closer machines get their air too.
the power, when 7 of 10 machines are running. Höcker fans run on variable speed drives, so they slow down as gates close instead of pulling full pressure all shift.
Duct friction at 4,500 feet per minute
| Duct size | Airflow | Loss per 100 ft |
|---|---|---|
| 4 in | 390 | 8.9 in. wg |
| 5 in | 610 | 6.8 in. wg |
| 6 in | 880 | 5.4 in. wg |
| 8 in | 1,570 | 3.8 in. wg |
| 10 in | 2,450 | 2.9 in. wg |
| 12 in | 3,530 | 2.3 in. wg |
| 16 in | 6,280 | 1.6 in. wg |
| 20 in | 9,820 | 1.2 in. wg |
| 24 in | 14,140 | 1.0 in. wg |
Round galvanized duct, standard air. Smaller ducts lose far more per foot, which is why branches stay short and mains get bigger.
Show the math and assumptions
Loss factors come from the ACGIH Industrial Ventilation manual, applied by Höcker North America.
Air speed = CFM ÷ duct area. Velocity pressure (VP) = (air speed ÷ 4,005)² in. wg. Every loss below is a factor times the VP of the duct it happens in.
| Loss | Factor |
|---|---|
| Machine hood (plain duct end plus getting the air moving) | 0.93 + 1.0 = 1.93 VP |
| Rigid duct friction, per foot | 0.0307 × speed0.533 ÷ CFM0.612 VP |
| Flex hose, per foot | 3 × rigid duct |
| 90° elbow (5-piece, 1.5 × diameter radius) | 0.24 VP |
| 45° elbow | 0.12 VP |
| Branch entry: 30° wye, 45° wye, 90° tee | 0.18, 0.28, 1.00 branch VP |
| Speeding up into a faster main | main VP minus branch VP, when higher |
| Collector and filters | 4 in. wg unless you change it |
Total static pressure = branch losses + main losses + collector loss. Fan brake horsepower = CFM × static pressure ÷ (6,356 × fan efficiency), with 65%% efficiency unless you change it. The motor is the next standard size up.
The main is figured at full system airflow along its whole length, which runs slightly high when your main steps down in size toward the far machines. In the main, count each 45° elbow as half a 90°. Open blast gates add almost nothing. Standard air at sea level; high altitude and hot air change the numbers.
Run more numbers
Questions
Dust collection static pressure FAQ
What is static pressure in dust collection?
It's the resistance your fan has to pull against, measured in inches of water gauge (in. wg), also called inches of water column (in. WC). Ducts, elbows, hoods and filters all add to it.
What static pressure should my dust collector have?
Enough to pull its full airflow through your longest run plus its own filters. Add up that run in the calculator and pick a fan rated for your CFM at that pressure. Until the duct runs are known, Höcker plans fans at 12 in. wg.
How do I calculate static pressure for my duct system?
Add up the losses along your longest run: machine hood, duct and flex hose friction, elbows, the branch entry, the main duct and the collector. Each one is a factor times velocity pressure, (air speed ÷ 4,005)².
Why do I only add up the longest run?
Air flows through every open branch at the same time, so the fan only has to beat the hardest path. If it can pull that one, it can pull the shorter ones.
How much static pressure does flex hose add?
About three times as much as the same length of rigid duct. Keep flex hose to the short drop at the machine.
What air speed should dust collection ducts run at?
At least 4,000 feet per minute, so chips and dust stay in the air instead of settling. Höcker designs branches and mains at 4,500.
What size fan do I need for my static pressure?
Brake horsepower = CFM × static pressure ÷ (6,356 × fan efficiency). For example, 6,000 CFM at 11 in. wg and 65% efficiency needs about 16 BHP, so a 20 HP motor.
How accurate is the static pressure estimate?
It's a planning number for standard air in round galvanized duct. Altitude, hot air, duct seams and how full your filters are all change the real reading.
Sources: ACGIH, Industrial Ventilation: A Manual of Recommended Practice for Design (velocity pressure method, Loeffler duct friction equation, hood, elbow and branch entry loss factors); Spiral Manufacturing engineering data for gored elbows.