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Studio Ventilation Design for Lampworking: Hood, Fan, Duct, and Make-Up Air

How to design lampworking studio ventilation: capture hood, fan, ducting, and make-up air, honest community CFM ranges, duct losses, and smoke testing.

cluster · published

By GlassTorches Editorial · Updated

Studio Ventilation Design for Lampworking: Hood, Fan, Duct, and Make-Up Air

Short answer: A working lampworking ventilation system is four components designed together: a capture hood that gathers the flame’s plume, a fan sized to real-world losses, ducting that never necks down in the direction of flow, and a make-up air path that replaces every cubic foot you exhaust without starving or backdrafting your furnace or water heater. Community practice puts a single torch station in the rough 300–600 CFM range, and standard overhead hoods at 100–125 CFM per square foot of hood face — figures that come from community experience and industrial-hygiene math, not manufacturer specifications. Design the system, then prove it with smoke before you trust it with your lungs.

This is the design deep-dive behind the ventilation sections of our glass torch safety setup checklist and the home studio in a small space guide: those tell you that you need ventilation; this one walks through how to design it.

What you’re actually ventilating: NO2 first, CO second

It helps to know what the system has to remove. Per the ISGB safety manual (Stan Wolfersberger), as cited in community ventilation guides, the chief “bad actors” from a high-temperature torch flame are nitrogen oxides — especially nitrogen dioxide (NO2) — a severe respiratory irritant with a very low acceptable air concentration. For scale, NIOSH lists a 15-minute short-term exposure limit of just 1 ppm for NO2, with health effects that include eye, nose, and throat irritation, decreased pulmonary function, chronic bronchitis, and pulmonary edema (NIOSH Pocket Guide).

Carbon monoxide matters too, but the same community sources note that documented CO poisonings trace to faulty furnaces and water heaters, not torches — a torch tripping a CO monitor is unlikely. That doesn’t make a CO detector optional (it’s cheap insurance, and as you’ll see below, your exhaust fan can create a CO problem at the water heater if make-up air is wrong). It means NO2 — invisible and hard to sense — is the contaminant your hood and fan are really sized for, which is why “I don’t smell anything” is not a ventilation test.

The four-component system

Community authority Mike Aurelius (Chaotic Glass) defines a glassworking ventilation system as four parts, and the definition is worth internalizing because most failed setups are missing one of them:

  1. A method of gathering and concentrating the fumes — the hood.
  2. A fan to pull (or push) them.
  3. Ducting to route them outside.
  4. A source of fresh replacement air — make-up air.

A powerful fan with no hood captures little; a beautiful hood with a starved room moves almost nothing; a good hood and fan strangled by undersized duct underperforms both. Every section below is one of these four components. Source: Chaotic Glass ventilation primer.

Hood design and placement

The hood is where capture succeeds or fails, and geometry matters more than raw fan power:

  • Add sides and a back. An open canopy pulls air from every direction, most of it clean room air. Sides and a back on the hood direct the airflow across the flame and greatly increase system efficiency.
  • Get close, or pay in CFM. Overhead hoods hung 4–6 feet above the work surface need much higher airflow than close-capture designs, because the plume has that much more distance to wander and cross-drafts have that much more opportunity to steal it.
  • Use a slot, not a hole. A slot running across the width of the hood draws fumes across the entire hood face instead of concentrating suction at one fixed spot.
  • The gold standard is a five-sided enclosure. One well-known community design (Michel Sun’s lampworking ventilation guide) is a fully enclosed five-sided hood with only the front open, modeled on laboratory fume hoods — the torch effectively sits inside the hood, and the open face is the only place air can enter.

Sources: Chaotic Glass, overhead hood design and Michel Sun’s ventilation guide.

Capture velocity: the math under the rules of thumb

The industrial-hygiene math behind every hood-sizing rule is simple:

Required CFM = hood face area (sq ft) × capture velocity (feet per minute)

Capture velocity is the air speed needed at the contaminant source — at the flame — to overcome room currents and pull the plume into the hood. ACGIH-derived guidance (via CCOHS, Industrial Ventilation – Hoods) gives roughly:

Release conditionCapture velocity
Contaminant released into still air, practically no room currents~100 fpm
Low-velocity release into moderately moving air (welding-like)100–200 fpm
Commonly treated floor — below this, capture fails50 fpm

A torch flame is closer to the welding-like case than the still-air case: it produces a hot, rising plume in a room with real drafts. This is why hood face area drives everything — double the open face and you double the CFM needed to hold the same capture velocity at the flame. It’s also why the five-sided enclosure wins: it minimizes face area and blocks the cross-drafts that would otherwise force you toward the high end of the velocity range. Source: CCOHS, Industrial Ventilation – Hoods.

Sizing: the honest community ranges

Editor’s note: every CFM figure in this section is community guidance — numbers worked out and shared by experienced lampworkers — not a manufacturer specification for any torch. No torch maker publishes a required CFM, and figures vary with hood design, duct run, and room. Where sources disagree, we give the range.

With that stated plainly, here is what community practice converges on:

  • Roughly 300 CFM minimum of air movement for a torch station.
  • A GTT Lynx-class torch: around 400 CFM.
  • Larger torches with the main burner running: around 500 CFM.
  • Two torches running simultaneously are additive — e.g. roughly 900 CFM for a pair of larger torches.
  • Lampwork Etc. threads corroborate 300–600 CFM as the working range for a single home station.

For overhead hoods, the community formula is at least 125 CFM per square foot of hood face area (some sources phrase it as 100–125 CFM/sq ft). Run the numbers and you see why hood geometry is a design decision, not decoration: a 16 sq ft overhead hood needs at least 2,000 CFM, while a close-capture or enclosed hood with a small open face gets the same protection from a fraction of that. Note that this formula is the capture-velocity math from the previous section in disguise — 125 CFM/sq ft is simply a 125 fpm face velocity.

Sources: Chaotic Glass, ventilation basics, Chaotic Glass, ventilation questions, Michel Sun, and Lampwork Etc..

Ducting: where rated CFM goes to die

A fan’s box rating is measured at 0.0 inches water column of static pressure — essentially a fan blowing into open air. Your real installation has a hood, straight duct, elbows, and transitions, and their combined resistance is the system’s static pressure. Against that resistance, the fan delivers significantly less than its rated CFM, so you must consult the fan performance curve (CFM at various static pressures), not the headline number.

The losses are figured like this in general HVAC practice:

  • Friction loss is tabulated per 100 feet of straight duct at a given CFM and diameter.
  • Each elbow counts as equivalent feet of straight duct added to the run.
  • Add the hood’s own entry loss, and the total is the static pressure your fan must overcome.

One community rule keeps you out of the worst trouble: the duct from hood to outside must never decrease in diameter in the direction of flow. A smaller-diameter duct on the suction side raises static pressure and air speed at the intake; a larger diameter on the exhaust side decreases static pressure. Necking a 10-inch hood outlet down to a 6-inch wall thimble can quietly cost you a large share of your airflow. Keep runs short, keep elbows few, and step diameters up — never down — toward the outlet.

Sources: Chaotic Glass primer, Engineering ToolBox, duct friction loss, and Central Blower, determining static pressure.

Make-up air: the component everyone forgets

For every CFM you exhaust, the same CFM of fresh outside air must enter the building. Seal the room and the fan doesn’t ventilate — it just depressurizes, moving less and less air while the gauge pressure drops. Community guidance is to keep the fresh-air path passive: open a dedicated inlet or window and let the exhaust fan pull what it needs, rather than fighting a second fan. Locate the inlet a minimum of 10 feet from any appliance exhaust duct, so you’re not re-inhaling flue gases.

The serious failure mode is backdrafting. An exhaust fan that depressurizes a house can pull its make-up air backwards down the water-heater flue or chimney — dragging combustion products, including CO, into the living space. This is exactly the case where a CO problem in a torch studio traces to the water heater, not the torch. The risk is real enough that the 2009 International Residential Code requires dedicated make-up air for kitchen exhaust fans over 400 CFM when atmospherically vented combustion appliances are present — and note that 400 CFM sits squarely inside the lampworking range above. Sealed-combustion / direct-vent appliances eliminate the backdraft risk, which is worth knowing if you’re choosing equipment for a studio building.

Sources: Chaotic Glass, make-up air issues and Green Building Advisor, All About Makeup Air.

Prove it with smoke

Design gets you close; testing tells you the truth. Smoke pens, sticks, and puffers produce visible, non-corrosive smoke used to verify airflow direction and confirm that the flame’s thermal plume is completely captured and contained by the hood. Standard fume-hood practice is to release smoke around the perimeter of the hood face and at the containment boundaries — corners, edges, the gap over your hands — because that’s where turbulence and escape paths show up first. Smoke curling out of the hood face and toward your chair is a failed test, whatever the fan’s rating says. Re-test whenever anything changes: a new torch, a moved bench, a different make-up air path.

Sources: NEBB, fume hood performance testing and Stanford EHS fume hood testing standards.

Fitting the system into a real room

If you’re building in a spare room or garage, the small-space studio guide covers how ventilation shapes the layout, and the torch setup guide covers plumbing the gas side of the same bench. Fan and airflow noise is also a real consideration in shared buildings — a factor worth weighing alongside torch noise itself (see quietest torches for shared studios).

As with everything safety-adjacent: this article is general design guidance, not engineering for your building. Your torch manufacturer’s instructions, your fan and appliance manufacturers’ documentation, and local mechanical and fire codes take precedence over anything here, and a qualified HVAC professional is the right call for anything touching combustion appliances.

Key takeaways

  • Ventilation is four components designed together: capture hood, fan, ducting, and make-up air — a missing one defeats the other three.
  • The driving contaminant is NO2 (NIOSH 15-minute limit: 1 ppm), not CO — you can’t smell your way to a verdict on the system.
  • Hood geometry beats fan power: sides and a back, close capture over a 4–6 ft canopy, a slot across the width, or a lab-style five-sided enclosure.
  • Sizing math: CFM = hood face area × capture velocity (~100–200 fpm for torch-like releases). Community practice: 300–600 CFM per station, 100–125 CFM per sq ft of hood face — community guidance, never manufacturer specs.
  • Fans are rated at zero static pressure and deliver less installed — read the fan curve, count elbows as equivalent duct feet, and never reduce duct diameter in the direction of flow.
  • Every exhausted CFM needs a passive make-up air path (inlet 10+ ft from appliance exhausts) — or the fan can backdraft your water heater’s flue and pull CO indoors.
  • Test with smoke around the hood face perimeter, and re-test after any change.

Sources

Editor’s note: all CFM figures in this article are community guidance and industrial-hygiene rules of thumb as of 2026 — no torch manufacturer publishes required ventilation CFM, and real systems vary with hood, duct, and room. Where sources disagree (300–600 CFM per station; 100–125 CFM/sq ft), we report the range. Follow your equipment manufacturers’ documentation and local mechanical and fire codes, and consult a qualified professional for any work involving combustion appliances.

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Sources