Laser exhaust fan & duct calculator
A fan’s “max CFM” is measured with nothing attached. Enter your duct, bends and flex hose, pick your fan, and see how much air it will actually move — and whether a bigger duct would help. Below it: what published studies measured in laser smoke.
1Your duct run
2Your fan and target
How the calculator works
Every duct resists airflow, and the resistance climbs steeply with flow. Every fan pushes less air the harder it has to push. The airflow you get is where the two meet.
The duct formula is Engineering ToolBox’s simplified equation for round galvanized duct. Trotec counts two 90° elbows as 12 ft of straight pipe, and a range-hood guide gives 2.5 ft for a 45° elbow. Stretched flex hose is rougher than metal duct (we estimate 1.7 × from the Darcy–Colebrook equation), and LBNL’s tests on 6" flex duct found that ordinary compression raises the pressure drop about four times and heavy compression close to ten times (coefficient 25.35 for 6", 21.61 for 8"; no data for 3" or 4", where it is likely worse, so we use the 6" value). Trotec’s rule of thumb counts 5 ft of flex as 15 ft of straight pipe without saying how compressed it is; our “normal” setting is harsher. If your laser’s manual gives airflow at a pressure, the calculator adds that pressure so the comparison is fair. No hobby fan maker we found publishes a full fan curve, so the fan is a straight line between its two ratings; real curves usually bulge above it.
What laser makers ask for
| Machine or fan | Airflow | Duct |
|---|---|---|
| Universal Laser Systems VLS desktop | 150 / 250 CFM at 6 in. w.c. (1.5 kPa) | 3" port |
| Universal Laser Systems VLS platform | 250 / 500 CFM at 6 in. w.c. | 4" port(s) |
| Epilog Fusion Edge, Fusion Pro 24/36, Zing, Mini, Helix | 350–400 CFM | — |
| Trotec (20 × 32 in. table, example) | 600 CFM at 6 in. w.c. | 4" or 6" metal duct |
| xTool SafetyPro IF2 fan | 140 CFM free air, 122 CFM on the laser | 3" |
| Glowforge (manual, as quoted) | No CFM given; at most two 90° bends (three with the Compact Filter) | 4" hose |
Professional makers state airflow at a pressure, such as 6 in. of water. A hobby inline fan rated 400 CFM with a maximum pressure of about 2 in. of water does not meet a “250 CFM at 6 in.” requirement.
Duct rules that matter most
- Go to 6". At the same airflow 4" duct loses about seven times more pressure per foot (our calculation from the duct formula). Trotec suggests 6" for runs over 35 ft.
- Pull flex hose tight, or replace it. Trotec counts 5 ft of flex as 15 ft of straight pipe.
- Few, smooth bends. Glowforge’s manual allows at most two 90° bends on its hose.
- Fan at the outside end. Trotec puts the fan at the end of the duct so the duct runs under suction: a leak pulls room air in instead of pushing smoke out.
- Damper and make-up air. Use a wall cap or vent hood with a damper, and leave a path for replacement air into the room, or the fan will starve in a tight house.
What is actually in laser smoke
| Study | What was measured |
|---|---|
| Acrylic, 60 W CO2 (UCLA, 2023) | Particles of 10–420 nm in the room rose sharply after the lid was opened; peaks of 3,515–18,143 particles/cm³. Methyl methacrylate was near the instrument’s 0.4 ppm detection limit, far below the OSHA limit of 100 ppm. |
| Cardboard, wood, plastic, glass, 40 W desktop CO2 (2024) | Inside the closed machine without exhaust: respirable dust up to 254 mg/m³ (cardboard) and 164 mg/m³ (wood); CO 24–32 ppm (cardboard and wood; not detected for plastic and glass); VOCs highest for plastic. Exhaust cut dust by 61 % on average and brought CO and VOCs below detection. |
| Fabrics and polymers, 25 W CO2 (NIOSH, 1997) | Up to 40 compounds per material, including hydrogen cyanide (felt 15 ppm, Formica 8–10 ppm inside the enclosure), formaldehyde, benzene and HCl. Duct residue was acidic and corroded copper. |
| Makerspace with local exhaust (Harvard GSD, 2019) | In the laser room (shared with 3D printers): PM2.5 at most 0.034 mg/m³, against 0.025 in a control office, and formaldehyde 4.5 ppb. Ultrafine particles were higher than in the office. |
| Paperboard, model-making lab (2024) | Particles, formaldehyde and VOCs rose with board thickness. An air purifier cut particles but not formaldehyde or VOCs. |
Three lessons run through these studies. With the lid closed and the exhaust running, levels dropped sharply. Room levels rose when the lid was opened, so keep the exhaust running after the job ends and wait for the enclosure to clear before opening it. And the purifier in the 2024 study cut particles but not formaldehyde or VOCs; the US EPA notes that filtration does not replace ventilation.
Almost every published measurement is of a CO2 laser. We found no peer-reviewed study of a blue diode engraver. Diode lasers burn the same materials, so the same chemistry applies, but how much a 10–20 W diode emits has not been measured.
Exposure limits for comparison
| Substance | OSHA limit | NIOSH recommendation |
|---|---|---|
| Methyl methacrylate | 100 ppm (8 h) | 100 ppm (10 h) |
| Formaldehyde | 0.75 ppm (8 h); 2 ppm short-term | 0.016 ppm (potential carcinogen); 0.1 ppm ceiling |
| Carbon monoxide | 50 ppm (8 h) | 35 ppm; 200 ppm ceiling |
| Hydrogen chloride | 5 ppm ceiling | 5 ppm ceiling |
| Hydrogen cyanide | 10 ppm (8 h) | 4.7 ppm short-term |
These are workplace limits for adults, shown for scale. The study figures above were mostly measured inside the machine, not in the room.
FAQ
- How many CFM do I need for a laser engraver exhaust?
- Use your laser maker’s figure. Published examples include 150 CFM at 6 in. of static pressure for Universal Laser Systems desktop machines and 350–400 CFM for most Epilog machines; larger machines ask for more. If the figure is given at a pressure, enter that pressure in the calculator too. A hobby fan’s “max CFM” is measured with no duct, so it delivers much less once the duct, bends and flex hose are connected.
- Should I use a 4 inch or 6 inch duct for a laser?
- Six inch if you can. At the same airflow, 4" round duct loses roughly seven times more pressure per foot than 6". Trotec suggests 6" duct for runs over 35 ft.
- Does a laser air purifier remove all the fumes?
- No. A 2024 study of laser cutting paperboard found that an air purifier significantly reduced particles but not formaldehyde or VOCs. The US EPA notes that filtration does not replace ventilation. Vent outside whenever you can.
- When is it safe to open the laser lid after cutting?
- Keep the exhaust running and wait until the smoke has cleared. A UCLA study found a sharp rise in fine particles (10–420 nm) in the room after the lid of a CO2 laser was opened, even with an extractor running during the cut, and a NIOSH study found methyl methacrylate escaping when the lid was opened before the enclosure had cleared.
Sources
- Engineering ToolBox, Duct friction loss.
- Trotec, Laser exhaust system information.
- Abushakra, Walker & Sherman, Compression effects on pressure loss in flexible HVAC ducts (LBNL).
- KitchenAid range hood duct guide (equivalent lengths of elbows, 35 ft for 6" round).
- AC Infinity, Cloudline S4 and S6 ratings; xTool SafetyPro IF2 ratings as listed by a reseller quoting xTool.
- Munoz et al., Characterization of emissions from CO2 laser cutting acrylic plastics, ACS Chemical Health & Safety, 2023.
- O’Neill et al., Respirable particles and gas contaminants emissions from a desktop laser cutter and engraver, Aerosol and Air Quality Research, 2024.
- Kiefer & Moss, Laser generated air contaminants released during laser cutting of fabrics and polymers, Journal of Laser Applications, 1997.
- Jeong et al., Indoor pollutant emissions in response to laser cutter operating conditions, Environmental Pollution, 2024.
- TRC Environmental for Harvard GSD, Indoor air quality assessment during fabrication activities, 2019.
- US EPA, Guide to air cleaners in the home; NIOSH Pocket Guide (linked in the table).
Last checked 2026-10-27 · Calculated values; no machine was used to make this page. See also what not to laser cut.