Short answer: A torch’s oxygen demand, measured in liters per minute (LPM), scales with how big the torch is, how many (and how large) its jets are, and how hard you actually run it. At the largest usable flame, a small single-stage bench torch draws roughly 5 to 10 LPM (the GTT Cricket ~5.5 LPM, the Bethlehem Alpha ~10 LPM), a two-stage mid torch roughly 15 to 30, and a big multi-stage burner 40 LPM and up (the GTT Delta Mag ~54 LPM), which is far beyond one concentrator and points to concentrators plumbed in parallel or compressed tanks. Run smaller than full flame and you draw less, so size your supply to meet or exceed the flame you actually run, with a little headroom.
This article is about demand: how much oxygen your torch wants and why. The companion piece, oxygen concentrator vs tanks for lampworking, covers supply: which source to run once you know your number, and the oxygen concentrator LPM guide covers matching one or more concentrators to that number.
What LPM actually measures
LPM is the volume of oxygen flowing to the torch each minute. A flame is just fuel and oxygen combusting; the more flame you want, the more of both gases you have to push through the torch. The oxygen side of that equation is what your supply has to satisfy, and it’s the side that usually becomes the bottleneck, because oxygen is the harder gas to produce or store in volume.
Every flameworking torch has a range of oxygen draw: a gentle, small flame uses little; the same torch opened up wide uses much more. So “how many LPM does my torch need” really means “how many LPM does my torch need at the flame size I intend to run.”
Why bigger torches need more oxygen: it’s the jets
The single best predictor of a torch’s appetite is its jets, the small orifices in the torch face where the gases meet and burn.
- More jets means more points of combustion, so more total gas flows.
- Larger jets pass more gas each.
- More stages (multi-stage torches layer a center fire and outer rings of jets) stack additional jets you can bring online for a bigger flame.
GTT’s own Flow Rate Chart shows the pattern inside one maker’s line, measured at the largest usable flame on propane:
| Torch | Jets | Stages | Oxygen at largest usable flame |
|---|---|---|---|
| GTT Cricket | 5 | 1 | ~5.5 LPM |
| GTT Phantom | 22 | 2 | ~16.5 LPM |
| GTT Mirage | 40 | 2 | ~26 LPM |
| GTT Delta Mag | 88 | 3 | ~54 LPM |
That’s the whole mechanism: more and larger jets, lit harder, equals more oxygen per minute. The chart gives cubic feet per hour; our catalog converts to LPM (CFH x 0.4719).
Mix type matters here too. If you’re weighing flame styles, see surface mix vs premix torches, but for sizing purposes, the thing that drives LPM is total jet capacity and how wide you run it, regardless of where the gases mix.
How to find your torch’s recommended LPM
The right source is the manufacturer’s spec sheet for your exact model. Some makers publish a flow figure (and often a fuel pressure) per torch; plenty do not, and the ones that do are not all quoting the same thing. A full-flame consumption number, a largest-usable-flame number, and a supply recommendation are three different claims, so check which one you are reading before you design around it.
Our catalog’s oxygen figures come from the manufacturer’s own pages and charts where we have them: GTT’s Flow Rate Chart, Bethlehem’s full-flame tanked-oxygen figures (the Bethlehem Champion at ~40 LPM, for example), and Carlisle’s listed standard oxygen use (the Carlisle Mini CC at ~7 LPM). Where a maker publishes nothing, the figure is our labelled estimate, placed against a comparable torch; the Nortel Minor page is one. Either way it is a single figure at the largest usable flame, not a minimum, and a torch’s real draw still moves with flame size, fuel pressure and jet condition. Before you buy a supply around a number, confirm your exact torch’s oxygen requirement with the manufacturer.
When you do find a figure, size for the top of your intended flame, not the minimum. If a torch is happy at, say, a modest flow for a small flame but wants much more wide open, and you plan to run it wide open, plan for the higher number plus headroom.
What happens when you run oxygen-starved
If your supply can’t deliver the LPM the flame is calling for, the torch doesn’t politely run smaller; it runs badly. An oxygen-starved flame is typically:
- Lazy, cool, and lengthy instead of tight and hot,
- Sputtering or fluttering as a concentrator’s internal tank empties and the sieve beds cycle,
- Slow to melt boro or larger gathers, frustrating your work,
- and sometimes sooty or unstable, never quite locking into a clean cone.
People often blame the torch when the real problem is supply. A powerful torch on inadequate oxygen performs worse than a modest torch that’s properly fed, which is exactly why we tell people to settle their oxygen reality before chasing a bigger torch. Source: Lampwork Etc..
Mapping LPM demand to a supply choice
Once you know roughly how many LPM your torch wants, you can map it to a supply. The full comparison lives in the concentrator-vs-tanks guide; here’s just enough to connect demand to options:
- One oxygen concentrator typically delivers up to roughly 5 to 10 LPM, depending on the unit, and purity tends to sag as you push it toward its ceiling. That covers small and many mid torches.
- Several concentrators plumbed in parallel add their flows together (two ~5 LPM units ≈ 10 LPM). Important: parallel plumbing adds flow, not pressure; concentrators are low-pressure devices and can’t simply be cranked up.
- Compressed oxygen tanks deliver high flow at high, consistent purity on demand, which is what thirsty production flames need; the tradeoff is refills, handling, and high-pressure safety (oxygen tanks, suppliers and costs covers the running cost).
- Bulk / liquid oxygen is for serious production where even banks of tanks become a chore.
As a rough shape: demand at or below a single concentrator points at one concentrator; a bit beyond that points at two units or a modest cylinder; well beyond a concentrator’s reach points at tanks, a bank, or bulk. Treat that as orientation, not arithmetic. Flow is only one of the inputs: delivered pressure and purity at load matter too, and parallel concentrators add flow without adding pressure, so two 5 LPM units are not interchangeable with one 10 LPM unit for a torch that wants pressure. Confirm against your torch’s manual and your own supply. Source: The Crucible.
A qualitative guide by torch class
Grouping torches by class turns those per-model figures into a supply decision. Find roughly where your torch sits:
| Torch class | Catalog examples (largest usable flame) | Typical supply that comfortably feeds it |
|---|---|---|
| Small bead / minor-class bench torch, small surface-mix starter | Cricket ~5.5 LPM, GTT Bobcat ~8.5 LPM, Alpha ~10 LPM | One concentrator |
| Mid-size bench surface-mix (versatile soft + small boro) | GTT Cheetah ~13 LPM, Phantom ~16.5 LPM | One capable concentrator, sometimes two |
| Larger multi-stage surface-mix (pipes, functional, sculpture) | Mirage ~26 LPM, Bethlehem Bravo ~30 LPM, Champion ~40 LPM | Multiple concentrators in parallel, or tanks |
| Large / production burners | Delta Mag ~54 LPM, Bethlehem Grand ~60 LPM | Tanks, banks of cylinders, or bulk oxygen |
- Small / bead / minor class, low demand. These are the sweet spot for a single concentrator. This is the classic home-studio setup: one machine, no cylinders, work as long as you like. GTT says the Cricket was designed around a 5 LPM, 5 psi concentrator, and Bethlehem says a machine that makes at least 5 LPM at 5 psi can feed its low-pressure surface-mix line; below full flame, that single small machine is enough.
- Mid bench surface-mix, moderate demand. Often a single capable concentrator, or a concentrator or two, depending on how big you run the flame. This is where people start plumbing units in parallel.
- Large / production, high to very high demand. Big multi-stage boro and production torches can demand far more oxygen than one concentrator delivers. Here you typically need tanks, bulk oxygen, or a bank of several concentrators plumbed together. Trying to feed a large production flame from a single concentrator simply won’t work.
The class boundaries are approximate and the catalog figures are full-flame numbers; your real draw depends on flame size and fuel pressure. Get the spec from the manufacturer, then size with headroom.
Putting it together
- Identify your torch class and, ideally, its manufacturer-published LPM range.
- Pick the flame size you’ll actually run and size to the top of that, not the minimum.
- Add headroom: a supply that’s always at its ceiling delivers a worse flame (and, for concentrators, worse purity).
- Choose the supply that meets the number, using the concentrator-vs-tanks guide, or the concentrator LPM guide if you are matching machines.
- Confirm everything with the maker before spending; this is the step that prevents an expensive mismatch.
This sequence is the third of the four questions in the glass torch buyer’s guide: decide your oxygen reality, then pick a torch that thrives on it.
Key takeaways
- LPM demand scales with torch size, jet count/size, and how hard you run the flame: on GTT’s own chart, oxygen at full flame climbs from about 5.5 LPM on the 5-jet Cricket to about 54 LPM on the 88-jet Delta Mag.
- Find your number on the manufacturer’s spec sheet, and treat any single published or community-circulated figure as a starting point to confirm with the maker.
- Running oxygen-starved gives a lazy, sputtering, poorly performing flame, and the torch gets blamed when the supply is at fault.
- One concentrator ≈ up to ~5 to 10 LPM; add units in parallel for more flow (not pressure), or move to tanks/bulk for thirsty production torches.
- Size by torch class and run the math toward your biggest intended flame, with headroom, then choose a supply that meets it.
Related guides
- Oxygen concentrator LPM guide: matching one or more concentrators to your number
- Oxygen concentrator vs tanks: choosing the supply
- Oxygen for lampworking: tanks, suppliers, and costs: what cylinder oxygen costs to run
- Oxygen concentrator brands compared: machines lampworkers actually use
- How many LPM does the GTT Bobcat need?: one torch worked through in detail
- Surface mix vs premix torches: flame styles
Sources
- Glass Torch Technologies, Flow Rate Chart (PDF; fuel and oxygen at the largest usable flame, measured on propane): https://www.glasstorchtech.com/_files/ugd/0f433e_940fa1536d544665a118116eb9542e62.pdf
- Bethlehem Burners, “Technical Information” (full-flame oxygen figures): https://www.bethlehemburners.com/resources/technical-information/
- Bethlehem Burners, Champion (full-flame tanked-oxygen consumption): https://www.bethlehemburners.com/torches/champion/
- Carlisle Machine Works, Mini CC (standard oxygen use): https://carlislemachine.com/as_benchburners/minicc.php
- The Crucible, “Lampworking/Flameworking tools & supplies”: https://www.thecrucible.org/guides/lampworking-flameworking/tools-supplies/
- Lampwork Etc., “Pre-mix vs Surface mix”: http://www.lampworketc.com/forums/showthread.php?t=191042
Editor’s note: torch oxygen figures come from manufacturer charts and pages where we have them and are labelled estimates where they are ours, as of 2026; makers measure differently (GTT at the largest usable flame on propane, Bethlehem as full-flame tanked consumption). Verify your torch’s recommended LPM and your supply options with the manufacturer before buying.