Natural Gas vs Propane Coffee Roasters: Fuel Conversion and Orifice Sizing

Two roasteries can buy the same 12 kg drum machine and end up with very different installs. One has a natural gas line at the meter. The other runs propane from a tank outside the building. The natural gas vs propane coffee roaster question rarely decides which machine you buy, but it decides what happens after the crate opens. Get it wrong and your roaster sits idle while you wait on a gas technician and the right parts.

This guide covers what actually changes between the two fuels at the burner, what to ask a seller before you commit, and how a fuel conversion gets done properly.

Key Takeaways

• Most gas roasters run on either natural gas or propane. The machine gets set up for one fuel at the factory, and a qualified technician can usually change it later.
• Propane carries about two and a half times the energy of natural gas per unit of volume, so the burner needs smaller gas openings and different pressure settings to deliver the same heat.
• A correctly converted roaster puts out the same BTU rating on either fuel. Switching to propane does not give you a hotter machine.
• Only a licensed gas technician should touch the burner, orifices or gas train. In many places, doing this work yourself is illegal as well as dangerous.
• Of the roasters listed on CoffeeTec between October 2024 and October 2026, about half ran on natural gas, a quarter on propane and one in five was all-electric.
• Ask every seller which fuel the machine is set up for, and whether anyone has converted it before.
• Propane brings extra rules around tank storage, handling and ventilation that natural gas does not.

What Changes Between Natural Gas and Propane at the Burner

Both fuels burn to heat the same drum. The difference sits in how much energy each one carries and how the burner has to meter it.

Propane packs more energy into the same volume. Roast Magazine puts propane at roughly two and a half times the calorific value of natural gas. That sounds like free power, and it is not. If you feed propane through a burner jetted for natural gas, you push far too much fuel into the combustion chamber. You get sooting, poor combustion and a real safety problem.

So the burner compensates. Propane setups use smaller gas openings, called orifices or jets, and run at a different supply pressure. Natural gas setups use larger openings at lower pressure. Match the orifice and the pressure to the fuel and both setups land on the same rated heat output. That is the point most forum threads miss. Converting your roaster to propane does not add power. It keeps the same power on a different fuel.

The burner type matters too. Traditional drum roasters mostly use atmospheric burners, which pull combustion air from the room around a manifold of jets. Power burners, also called fan-assist or pre-mix burners, use a blower and a mixing chamber, and a gas professional sets the fuel-to-air ratio with test instruments. Both types convert between fuels, but a power burner conversion involves more setup work because the air-to-gas mix has to be measured and dialled in again.

Natural Gas vs Propane Coffee Roaster: Side by Side

Neither column is the better choice in the abstract. The fuel already at your site decides it, and the machine follows.

Why Fuel Type Matters Before You Buy a Used Roaster

On a new roaster you pick the fuel at order time and the factory builds it that way. On a used machine, somebody else already made that choice, possibly decades ago, and possibly for a building nothing like yours.

That is why fuel type sits alongside batch capacity and power needs on every CoffeeTec listing, and why the roaster finder on the used coffee roasters collection asks what fuel you have at your site before it points you anywhere. A 22 kg Probat set up for natural gas is a different purchase for a rural roastery on propane than it is for a shop with a gas main at the kerb.

The gap between the two is usually bridgeable. It is rarely free, and it is never a weekend job. Plan for it before you agree a price, not after the freight arrives. Our guide to the hidden costs of buying a used coffee roaster covers gas line work and the other install items that catch first-time buyers.

Enter the fuel at your site and what the listing says below to see whether a conversion is involved and what it would cover.

What to Ask the Seller About Fuel Setup

Five questions cover almost every case. Ask them before you talk numbers.

• Which fuel is it currently set up for? Natural gas or propane. Not which fuel the model can run, which fuel this machine runs today.
• Has it been converted before, and by whom? A machine converted once by a licensed technician with a manufacturer kit is straightforward. A machine converted by a previous owner with parts from a hardware store needs a full inspection.
• What does the data plate say? The rating tag carries the BTU rating and the fuel the machine was built for. Ask for a clear photo of it.
• Is a manufacturer conversion kit still available for this model? For current models from Diedrich, Probat, US Roaster Corp or Mill City Roasters, usually yes. For a 1960s drum, often no, and your technician will source parts individually.
• What burner type does it use? Atmospheric or power burner. This changes how much setup labour a conversion takes.

No data plate, or one you cannot read? That happens on older drums, and it does not end the purchase. A gas technician can identify the burner setup from the components themselves. Ask the seller for clear photos of the burner assembly, the regulator and the gas valve instead, and send those to your technician before you commit.

Pair these with the broader mechanical checks in our used roaster safety checklist before you commit to anything.

How a Fuel Conversion Actually Works

Here is the honest version: you do not do this yourself. Working on a gas appliance burner without a licence is unsafe, and in many jurisdictions it breaks the law. Your insurer will also take a view if anything goes wrong afterwards.

What a licensed gas technician does, broadly:

1. Sources the right parts. A manufacturer conversion kit where one exists, or correctly specified components for that exact machine where one does not.
2. Changes the orifices or jets. Each burner opening gets swapped for the size matched to the new fuel.
3. Adjusts or replaces the regulator and gas valve. The two fuels run at different pressures, so the gas train has to suit the new supply.
4. Sets up the pilot or ignition assembly. Pilot orifices change with the fuel as well as the main burner.
5. Tests combustion and pressure. The technician verifies the machine fires at its rated BTU, burns cleanly and holds pressure, then checks every joint for leaks.
6. Updates the data plate and documents the work. Keep the paperwork. It matters for inspections, for your insurer and for the next owner.

Once the conversion passes, treat the machine as new to you and work through a proper startup. Our commissioning guide walks through seasoning and first roasts.

Where Conversions Get Complicated

Most conversions are routine. A few situations need more thought. The diagram below shows every part a conversion reaches, and where the afterburner sits outside it.

• The roaster has an afterburner. That is a second gas appliance with its own burner and its own orifices. Converting the roaster and forgetting the afterburner is a common and expensive oversight. Check the fuel on any afterburner listed separately as well.
• The machine is old enough that no kit exists. Vintage Probat, Gothot and Royal drums still roast beautifully, and parts get sourced individually rather than from a box. Budget more technician time.
• Nobody knows the conversion history. If a machine has changed hands several times and the data plate says one fuel while the hardware suggests another, have a technician inspect before it runs.
• Your propane tank cannot carry the load. A production roaster firing at high BTU draws hard on a tank. Tank sizing and vaporisation rate are a separate conversation with your propane supplier.
• You are moving to a site with a different fuel. Convert before the machine ships if you can. It is easier to schedule the work while the roaster is still accessible and not yet bolted into a new room.

Common Mistakes to Avoid

• Assuming propane means more heat. Set up correctly, both fuels hit the same rated output. The energy difference gets absorbed by orifice sizing, not passed on to the drum.
• Using a generic appliance orifice chart. Grill and fire pit charts circulate widely online. A roaster burner is not a grill burner, and the manufacturer's specification for your machine is the only chart that applies.
• Converting the roaster but not the afterburner. Two appliances, two conversions.
• Skipping the pressure test. Correct orifices with the wrong supply pressure still give you the wrong firing rate.
• Buying on price without checking the fuel. A cheaper machine on the wrong fuel is not cheaper once the technician invoice lands.

If you are still weighing fuel against going electric entirely, our electric vs gas coffee roaster guide compares install requirements and heat response across both.

Selling a Roaster? Put the Fuel Type in Your Listing

Sellers often leave fuel type out, then field the same question from every enquiry. Put it in the listing and you filter for serious buyers immediately.

Three things worth stating up front:

• The fuel the machine currently runs on.
• Whether it has been converted, when, and by whom.
• The BTU rating from the data plate, with a photo of the tag.

Buyers on propane and buyers on natural gas are both shopping. A clear fuel line tells each of them what the machine will cost to install, which is what they actually want to know. You can list your roaster on CoffeeTec with those details and reach buyers already browsing this category.

Find a Roaster That Matches Your Gas Supply

Browse current drum roasters and filter by what fits your site. Every listing shows batch size, year, condition grade and fuel type, so you can rule out an awkward install before you enquire. New to buying used equipment? Start with our complete used roaster buying guide.

The mix shifts with batch size. Across CoffeeTec roaster listings that record both fuel and capacity between October 2024 and October 2026, propane held roughly a fifth to a quarter of listings at every size. Electric thinned out above 4 kg, and natural gas rose to about four in five listings at 20 kg and up. If you are on propane, you have options at every size, and more of them involve a conversion as the drums get bigger.