BTU/min to BTU/h for Torch and Forge Burner Ratings

Reading a Torch or Forge Burner Rating in BTU per Hour

Burner and torch makers like the per-minute figure because it sits next to the flame you are looking at. Everything downstream of the burner — the regulator on the cylinder, the hose bore, the cylinder itself and the gas supplier's paperwork — is written per hour. A metalworker putting together a propane setup for a forge, a melting furnace or a heavy heating torch spends a good part of the job moving between those two numbers.

Conversion factor: 1 BTU/min = 60 BTU/h — multiply by 60. A ¾ in. venturi forge burner quoted at 1,500 BTU/min is running 90,000 BTU/h, roughly 4.2 lb of propane an hour, which empties a 20 lb cylinder in under five hours.

What the Hourly Figure Decides

Regulator capacity

Adjustable high-pressure regulators are catalogued by BTU/h at a stated outlet pressure. A burner asking 180,000 BTU/h wide open will starve behind a regulator rated below that.

Cylinder vaporisation

A cylinder is not a pipe — it has to boil liquid propane fast enough to keep up. That withdrawal limit is quoted in BTU/h and drops as the cylinder empties and as the air gets colder.

Fuel draw and run time

Propane carries roughly 21,500 BTU per pound and about 91,500 BTU per US gallon, so an hourly firing rate turns straight into pounds burnt and hours of work per bottle.

Forge chamber size

Forge builders work to a rough hourly heat input per unit of chamber volume, so the BTU/h number tells you whether one burner covers the shell you welded up or you need a second.

From a Burner Spec Sheet to a Propane Order

The sequence below is the one that matters in the shop: get to BTU/h first, then let that number pick the regulator, the bottle and the length of the working session.

Enter the per-minute rating off the burner label

Type the BTU/min figure on the left — 400, 1,500, 3,000 — and the hourly value appears as you type. A comma or a dot both work as the decimal mark, and spaces inside the number are ignored.

Hold it against the regulator and hose

Compare the hourly figure with the BTU/h capacity printed for the regulator at the pressure you actually run, and with the hose bore. A venturi forge burner wants an adjustable 0–20 psi regulator, not the fixed low-pressure one that comes on a barbecue.

Turn the hourly figure into pounds of propane

Divide by about 21,500 for pounds an hour, or by about 91,500 for US gallons. The copy button hands over the bare number with no unit attached, so it drops straight into a fuel log or a job costing sheet.

Go back the other way for an hourly catalogue

Plenty of forced-air and industrial burners are listed in BTU/h instead. Press the swap button (↔) to run BTU/h → BTU/min and put such a rating on the same footing as the per-minute torch label beside it; by hand, divide by 60.

Rated is not what you burn all day: a quoted rate is wide open at the design pressure. Forge work usually settles well below that once the chamber is hot, so size the gas train on the rated figure and estimate fuel use on a lower average.

Firing Rates of Torches, Forges and Process Burners

Typical wide-open figures across the range a metalworker meets, from a hand torch for silver solder up to a forced-air burner on a heat-treat oven. Fuel draw is worked out at roughly 21,500 BTU per pound and 91,500 BTU per US gallon of propane.

Burner or torch	Firing rate (BTU/min)	Firing rate (BTU/h)	Propane draw
Pencil-flame hand torch	150 BTU/min	9,000 BTU/h	0.42 lb/h (0.10 gal/h)
Swirl-flame plumbing torch	400 BTU/min	24,000 BTU/h	1.1 lb/h (0.26 gal/h)
Weed and roofing vapour torch	1,000 BTU/min	60,000 BTU/h	2.8 lb/h (0.66 gal/h)
Single ¾ in. venturi forge burner	1,500 BTU/min	90,000 BTU/h	4.2 lb/h (0.98 gal/h)
Two-burner blade forge, wide open	3,000 BTU/min	180,000 BTU/h	8.4 lb/h (2.0 gal/h)
Ribbon-burner forge or small melting furnace	5,000 BTU/min	300,000 BTU/h	14 lb/h (3.3 gal/h)
Forced-air process burner	10,000 BTU/min	600,000 BTU/h	28 lb/h (6.6 gal/h)

Read down the fuel column and the practical limit shows up long before the burner does. A 20 lb cylinder holds roughly 430,000 BTU of propane, so it feeds the hand torch for days, the single forge burner for not quite five hours and the two-burner forge for a little over two. That is why shops running anything past the middle of this table move to a 100 lb cylinder or a manifolded pair.

What Helps When You Are Costing a Burn

Step through burner sizes without retyping

Both boxes stay live, so you can walk a whole catalogue page — 400, 1,000, 1,500, 3,000 BTU/min — and read off the hourly figure for each in a couple of seconds.

Flip it when the listing is hourly

The swap button turns the page round to BTU/h → BTU/min, the direction you want when a forced-air burner is quoted hourly and the torch next to it is quoted per minute.

Drop in kilowatts for an imported forge

The searchable dropdowns carry every power unit, so a European burner quoted in kW lands alongside your BTU figures — 1,500 BTU/min works out at about 26.4 kW.

Clean numbers for the gas paperwork

Copy lifts the plain value with no unit and no spaces, ready for a quote or the connected-load schedule a gas supplier asks for. Ctrl + C inside a field does the same.

Propane Supply Questions from the Shop Floor

Why does my forge lose pressure and frost the cylinder after twenty minutes?

You are drawing gas faster than the liquid inside can boil. Vaporisation depends on wetted wall area and the temperature difference to the surrounding air, so a full 20 lb cylinder in a warm shop typically sustains something like 50,000–60,000 BTU/h — under 1,000 BTU/min — and considerably less once it is half empty or the shop is near freezing. A 1,500 BTU/min burner simply outruns it. The answers are a larger cylinder, two bottles manifolded together, or short bursts with recovery time. Never warm a cylinder with a flame.

How long will a 20 lb propane cylinder run my forge?

Take the cylinder's energy content — about 20 × 21,500 = 430,000 BTU — and divide by the hourly firing rate. At 90,000 BTU/h that is roughly 4.8 hours wide open; at 180,000 BTU/h it is about 2.4. Real sessions stretch further because you throttle back once the forge is at heat, but plan the day on the wide-open figure and you will not run dry in the middle of a weld.

Can I put a forge burner on natural gas instead of propane?

Not without changing the orifice. Propane carries around 2,500 BTU per cubic foot against roughly 1,030 for natural gas, and household natural gas arrives at a few inches of water column rather than the several psi a venturi burner wants. Reaching the same BTU/h therefore needs a much larger jet and far more gas volume, which is why naturally aspirated natural-gas forges use oversized burners or a blower. Convert with parts made for the job rather than by drilling out the propane jet.

What regulator and hose does a 3,000 BTU/min burner need?

That is 180,000 BTU/h, so you want an adjustable high-pressure regulator with headroom above that at the outlet pressure you run — commonly a 0–20 or 0–30 psi unit — plus hose rated for high-pressure propane, usually 3/8 in. bore for a run of any length. Read the regulator's capacity table rather than its headline number, because capacity falls as the outlet pressure setting falls, and keep hose runs short so pressure at the burner still matches the gauge.

Why do torch makers quote per minute when the rest of the trade uses per hour?

Because a torch is a short-duty tool. Nobody runs a soldering torch for a solid hour, and the per-minute number stays small enough to compare at a glance — 150 against 400 reads more easily than 9,000 against 24,000. Fixed equipment that really does run for hours, and the gas trains feeding it, stayed with the hourly figure. Both describe the same rate of heat release; only the time base differs.

BTU per Minute to BTU per Hour