3D printer exhaust fan: what size and type to use

A 3D printer exhaust fan (also sold as an extractor or vent fan) needs to move only about 10 to 25 cubic feet per minute (CFM) to clear a desktop printer’s heat. That is 17 to 42 m³/h. Through an open outlet one 120 mm PC fan does it; behind a carbon filter or a hose, use a blower or a 4-inch inline fan.

What exhaust fan does a 3D printer enclosure need?

An enclosure needs an exhaust fan that moves about 10 to 25 CFM (17 to 42 m³/h) through its filter and duct. That much air holds a box with an 80 to 200 W printer on PLA at 40 °C in a 25 °C room. Open outlets need only a PC fan; filters and ducts need a blower.

The printer’s heat sets the airflow. nVent Hoffman, an enclosure maker, sizes fans with this formula. The temperature rise is the enclosure limit minus the room temperature:

CFM = 3.16 × watts ÷ temperature rise (°F)

Bambu Lab A1 printing PLA, 95 W, box at 40 °C in a 25 °C room (27 °F rise):
3.16 × 95 ÷ 27 = 11.1 CFM (18.9 m³/h)

The watts are each printer’s average power while printing PLA, from Bambu Lab’s wiki:

Printer, PLA	Average power	Exhaust needed, 40 °C box, 25 °C room
Bambu Lab A1 mini	80 W	9.4 CFM (15.9 m³/h)
Bambu Lab A1	95 W	11.1 CFM (18.9 m³/h)
Bambu Lab P1S	105 W	12.3 CFM (20.9 m³/h)
Bambu Lab H2D	197 W	23.1 CFM (39.2 m³/h)

The 40 °C limit sits just under the roughly 45 °C at which Bambu Lab says most PLA softens. The room temperature moves the answer as much as the printer does: the same A1 needs 16.7 CFM (28.3 m³/h) in a 30 °C room. Size for the warmest day the printer runs. The enclosure fan calculator works it out from your printer’s watts and room temperature, with a margin for a filter.

Fan types compared by airflow and static pressure

Static pressure is the resistance a fan can push against, measured in inches of water gauge (in. w.g.) or pascals (Pa); 1 in. w.g. is 249 Pa. Every filter and hose adds resistance. Fan maker Oriental Motor explains that airflow peaks at zero static pressure and drops to zero at the fan’s maximum static pressure. The real flow sits where the fan’s curve meets the resistance of your filter and duct.

An axial fan is the propeller type used in PC cases. A blower is a centrifugal fan that throws air out sideways through a scroll housing, and an inline fan sits inside the duct run. In the makers’ figures below, the first four fans list free-air flow (nothing in front of the fan) and their maximum pressure. Bathroom fans instead state airflow at a working pressure:

Fan	Type and supply	Rated airflow	Pressure figure
ARCTIC P8, 80 mm	Axial, 12 V DC, 0.14 A	23.4 CFM (39.8 m³/h)	0.075 in. w.g. (1.90 mm H₂O)
ARCTIC P12, 120 mm	Axial, 12 V DC, 0.16 A	56.3 CFM (95.7 m³/h)	0.087 in. w.g. (2.20 mm H₂O)
Delta BFB1024H, 97 x 94 mm	Blower, 24 V DC, 9.6 W	25.4 CFM (43.2 m³/h)	1.00 in. w.g. (25.4 mm H₂O)
AC Infinity Cloudline S4, 4 in. duct	Inline, 100 to 240 V AC, 28 W max	226 CFM (384 m³/h)	0.90 in. w.g. (223 Pa)
Broan AE80B, 4 in. duct	Bathroom fan, 120 V AC, 24.7 W	80 CFM (136 m³/h) at 0.1 in. w.g.	60 CFM at 0.25 in. w.g.
Panasonic FV-0511VQ1, 4 or 6 in. duct	Bathroom fan, 120 V AC, 10.6 W at 110 CFM	50, 80 or 110 CFM at 0.1 in. w.g.	53, 83 or 111 CFM at 0.25 in. w.g.

A small exhaust fan is enough when nothing blocks it. With only a grille in its way, the 80 mm P8’s 23.4 CFM free-air rating is about twice what the A1 mini, A1 or P1S needs.

Why a PC fan stalls behind a carbon filter or long duct

An axial PC fan tops out at a fraction of a blower’s pressure. The P12’s maximum, 0.087 in. w.g., is below the 0.1 in. at which bathroom fans are rated, and Panasonic cites industry research putting typical bathroom fan installations at 0.20 to 0.375 in. As the resistance nears a fan’s maximum pressure, its flow falls toward zero. A filter or duct that barely slows a blower can choke a PC fan, because the Delta blower and the Cloudline inline fan make more than ten times the P12’s pressure.

Filters cost airflow even on a fan built for them. Pfannenberg’s 24 V PF 22000 filter fan moves 61 m³/h (36 CFM) unimpeded and 44 m³/h (26 CFM) through its standard filter mat, 28% less. Oriental Motor names the filter as the accessory with the largest pressure loss. We found no published pressure drop for a carbon filter on a printer enclosure, so get the figure from the filter maker and check that the fan’s curve still shows your CFM at that pressure.

Fan speed for ABS and ASA

For ABS and ASA the exhaust is there for fumes, not cooling, so it has to run slowly. Bambu Lab’s X1E heats its chamber to as much as 60 °C for these materials. To let a 200 W printer (the A1’s average on ABS) warm its box to 60 °C in a 25 °C room, the fan can move at most:

3.16 × 200 W ÷ 63 °F rise = 10.0 CFM (17.0 m³/h)

The walls shed some heat too, so the real limit is lower. At its full free-air rating of 226 CFM, a Cloudline S4 would hold the same box about 1.6 °C (2.8 °F) above the room. Buy a fan with speed control.

Washington State’s Department of Health, writing for schools, says the best practice is to enclose printers and exhaust their emissions directly outside. It adds that HEPA (high-efficiency particulate air) and charcoal filters help reduce hazards but are not sufficient under its code.

Can you use a bathroom exhaust fan for a 3D printer?

Yes, if it vents outdoors and is wired to code. A bathroom fan is a ducted blower rated at 0.1 inch of water static pressure, so it handles a hose or filter better than a PC fan. It runs on 120 V AC and typically moves 50 to 110 CFM, several times a printer’s heat load.

Bathroom fans are tested to the Home Ventilating Institute’s airflow procedure, HVI Publication 916, and their certified CFM is given at 0.1 in. w.g. ENERGY STAR adds a second test point: a certified bathroom fan must still deliver at least 70% of that airflow at 0.25 in. w.g. Broan’s AE80B moves 80 CFM at 0.1 in. and 60 CFM at 0.25 in., or 75%. Panasonic’s FV-0511VQ1 has a switch for 50, 80 or 110 CFM (85, 136 or 187 m³/h). Its motor speeds up when it senses static pressure.

Conditions for using one on a printer

• It must discharge outdoors. International Residential Code (IRC) Section M1501.1 requires the air from every mechanical exhaust system to be discharged outdoors. It may not go into an attic, soffit, ridge vent or crawl space. Broan’s instructions agree: ducted fans must always be vented to the outdoors.
• It is wired in, not plugged in. Both fans above run on 120 V, 60 Hz. Broan’s Model 690 instructions require a qualified person to do the installation and wiring, switch location included, under applicable codes. The unit must be grounded.
• Its mounting limits still apply. Broan rates the AE80B for ceilings, or for a wall when mounted 8 ft (2.4 m) or more above the floor. Its 690 kit must sit at least 5 ft (1.52 m) above the floor. Panasonic lists the FV-0511VQ1 as not for wall installation. A fan housing screwed to an enclosure on a bench falls outside these instructions, so check the limits in your model’s manual.
• It is for general ventilation. Broan’s caution reads: “For general ventilating use only. Do not use to exhaust hazardous or explosive materials and vapors.”
• It gets its own duct. Broan specifies the AE80B ducted to a roof or wall cap in 4 in. (102 mm) round duct. We found no code section or fan instruction that lets a printer fan share an existing bathroom fan’s duct. Before joining one, ask your local building department.
• It moves more air than the heat needs. The FV-0511VQ1’s lowest setting, 50 CFM, is 4.5 times the 11.1 CFM an A1 needs on PLA. At 50 CFM a 95 W printer’s box sits about 3.3 °C (6 °F) above the room: fine for PLA, too cold for a warm ABS chamber. Broan’s 690 instructions call for an on/off switch or a speed control.

DIY 3D printer exhaust fan

A DIY exhaust is a fan, a power source, an outlet high on the box and an inlet low on the opposite side. Through an open outlet, a 12 V 120 mm PC fan is the simplest build. For a filter or a hose, use a 24 V blower or an inline fan.

1. Pick the fan by its air path. An open grille or a short opening suits an axial fan like the P12. A carbon filter or a duct calls for a blower like the BFB1024H (1.00 in. w.g.) or an inline fan.
2. Power it at its rated voltage. Run a 12 V fan from a 12 V DC adapter rated above the fan’s current; the P12 draws 0.16 A. A 24 V fan can share a 24 V printer’s supply; the BFB1024H adds 9.6 W, or 0.4 A. Never wire a 12 V fan straight to 24 V, which doubles its rated voltage. The guide to what voltage 3D printer fans use covers step-down converters and matching a replacement fan. Add the fan’s watts in the power supply calculator before you put it on the printer’s supply.
3. Mount it high, as an exhaust. nVent Hoffman puts the inlet low on one side and the outlet high on the opposite side, so exhaust air does not loop back in, and makes the outlet at least as large as the inlet. For electrical cabinets Hoffman generally recommends blowing air in, to keep dust out. For printer fumes, pull air out instead: the box then sits below room pressure, and leaks draw room air in. Bambu Lab notes that when its X1E loses this negative pressure, some gases escape through gaps instead of passing through the filter.
4. Duct it outside for fumes. Run the hose to a window or wall opening, never into an attic or crawl space, which IRC M1501.1 bars. A 4-inch vent hose carries this airflow with little loss.

3D printer ventilation kits: what they contain and what to check

A ventilation or exhaust fan kit bundles the fan with the parts that carry air outdoors. For sizing the inline fan in one, see what size inline fan a printer needs. AC Infinity’s 4-inch Air Filtration Kit (AC-FKS4), sold for grow tents, shows what a 4-inch kit holds:

• A Cloudline inline fan rated 165 CFM (280 m³/h) and 324 Pa (1.30 in. w.g.), 100 to 240 V AC, with a 10-speed controller
• A carbon filter with a 38 mm charcoal bed, rated for 210 CFM maximum
• 25 ft (7.6 m) of 4 in. (102 mm) flexible duct
• Duct clamps, prefilter cloth, rope clip hangers and hanging straps

Check these specs on any kit before you buy:

• Airflow at pressure. Look for a fan curve or a CFM rating at a stated static pressure, not just free-air CFM. It has to beat the calculator’s figure with the filter in place.
• Static pressure. Compare it with the table above: the PC fans top out below 0.1 in. w.g. (25 Pa), while the blower and inline fans reach 0.9 to 1.3 in. (223 to 324 Pa).
• Duct diameter. Match the enclosure port, the hose and any window adapter. 4 in. is 102 mm.
• Speed control. A stepped controller or dial lets the same fan run fast for PLA and slow for a warm ABS chamber.
• Voltage. Both AC Infinity fans above plug into a wall outlet. A 12 V or 24 V DC fan needs an adapter or the printer’s supply.
• Filter rating against the fan. The filter’s maximum airflow should exceed the fan’s, as in the AC-FKS4: a 210 CFM (357 m³/h) filter on a 165 CFM fan.