If you install or service air conditioning and refrigeration systems, oxygen-free nitrogen is one of those essential products that appears on almost every job.

It is used to pressure-test pipework, flush moisture and debris from lines, and keep the inside of copper pipework clean during brazing.

Having the right cylinder on the van helps make the job faster, cleaner and easier to sign off. Arriving without enough gas, or with the wrong regulator, can quickly cause delays.

This guide explains what oxygen-free nitrogen is, why air conditioning engineers rely on it, which cylinder sizes are available, and how Adams Gas supplies it rent-free with local delivery.

What is oxygen-free nitrogen?

Nitrogen is an inert, non-flammable gas that makes up most of the air around us.

Oxygen-free nitrogen, often shortened to OFN, is a high-purity, dry grade of nitrogen with the oxygen and moisture removed.

This dryness and purity make it particularly useful for air conditioning and refrigeration work. With no oxygen present, it will not react with hot copper during brazing, and with no moisture present, it will not contaminate a sealed system.

On site, it may be referred to as OFN, dry nitrogen, air-con nitrogen or simply the nitrogen bottle. In practical terms, these all refer to a clean, inert gas used for testing and preparing pipework.

Why air conditioning and refrigeration engineers use nitrogen

OFN has three main uses in HVAC and refrigeration work.

Pressure and strength testing

Before a system is charged with refrigerant, engineers pressurise the pipework with nitrogen to check for leaks and confirm that the joints will hold.

Nitrogen is inert, more economical than refrigerant and safe to release, making it well suited to this type of testing.

Purging and flushing

Nitrogen can be blown through pipework to remove moisture, swarf and debris left from cutting and installation.

This helps prevent contamination reaching the compressor or expansion valve once the system is running.

Brazing under nitrogen flow

A gentle flow of nitrogen can be passed through copper pipework while brazing.

This helps stop oxide scale forming inside the pipe. If this scale, sometimes known as black soot, breaks loose, it can block the system. For this reason, brazing under nitrogen is widely regarded as best practice.

Because these are everyday tasks, most installers keep a nitrogen cylinder on the van. The main question is usually which size is best.

OFN nitrogen cylinder sizes

Adams Gas supplies oxygen-free nitrogen in a range of sizes, from small disposable bottles for occasional testing to large refillable cylinders and manifolded packs for busy commercial teams.

Disposable OFN cylinder, 0.95L

This single-use bottle is suitable for occasional testing, tight spaces and one-off jobs.

Disposable OFN cylinder, 2.2L

This single-use option is suitable for small installations, plumbers and air conditioning installers.

OFN cylinder, 9.4L

This refillable 137 bar cylinder is suited to regular service and installation work.

OFN cylinder, 20L

This refillable 200 bar cylinder is designed for full-time installers and larger systems.

OFN cylinder, 50L

This refillable 200 bar cylinder is suitable for high-volume commercial and workshop use.

Nitrogen manifolded cylinder pack

A manifolded cylinder pack is suited to fixed workshops and depots with heavy nitrogen demand.

The disposable 0.95L and 2.2L OFN bottles are designed for plumbers and air conditioning installers who only need nitrogen occasionally. They use a compact M10 x 1 RH thread connection and can be carried in a toolbox.

The refillable 9.4L, 20L and 50L cylinders are suited to engineers who use nitrogen regularly and want a lower cost per test. For depots and workshops with constant demand, a manifolded cylinder pack keeps several cylinders connected at the same time.

Disposable, refillable or rent-free: which should you choose?

The right option depends on how often nitrogen is used.

Disposable bottles make sense for occasional testing or for those who only carry out refrigeration work now and again. They involve no commitment and no returns, but the cost per litre of gas is higher.

Refillable cylinders are the standard choice for working installers. They provide far more gas for the money, and the empty cylinder can simply be swapped when required.

The drawback with refillable cylinders from many suppliers is cylinder rental. This ongoing charge continues whether the gas is being used or not.

Adams Gas offers rent-free oxygen-free nitrogen. Customers pay for the cylinder and the gas, with no standing rental and no long-term contract.

For tradespeople who pressure-test only a few times a week, removing the rental charge can save more over the year than the cost of the gas itself.

Regulators and what else you need

A nitrogen cylinder cannot be used safely on its own because the pressure inside the cylinder is too high for direct use.

A nitrogen regulator is required to reduce the pressure to a safe and controllable working level.

Adams Gas supplies a 300 bar single-stage nitrogen regulator with a twin-gauge design and 10 LPM flow, which is suitable for most air conditioning testing and purging work.

A typical OFN kit may also include charging hoses and, for brazing under flow, a low, steady trickle set on the regulator.

If you are unsure which regulator matches your cylinder outlet, Adams Gas can advise on the correct fitting.

Using nitrogen safely on site

Nitrogen is inert and non-flammable, but it is stored at high pressure and displaces oxygen. It must therefore be handled with care.

Always use a proper nitrogen regulator rather than relying on the cylinder valve to control pressure.

Secure cylinders upright and restrain them in the van so they cannot roll or fall.

Work in well-ventilated spaces, as a large nitrogen release in a confined area can reduce the available oxygen.

Follow the manufacturer’s test pressures for the equipment being worked on, together with the usual F-Gas and refrigeration procedures.

Keep cylinders away from heat sources and check hoses and fittings for damage before use.

Where to buy OFN nitrogen

Adams Gas is an independent bottled gas supplier serving trade and domestic customers across Kent and beyond.

For air conditioning and refrigeration engineers, Adams Gas offers:

• Rent-free cylinders with no standing charges or contracts
• A full range of OFN sizes, from disposable bottles to 50L cylinders and manifolded packs
• Local delivery and a nationwide stockist network

Customers can browse the nitrogen for air conditioning range, view all nitrogen cylinders or use the stockist finder to locate a nearby supplier.

If you are unsure which cylinder size or regulator you need, the Adams Gas team can help you choose the right option for the van.

Businesses interested in running a stockist counter and selling OFN and refrigeration gases to their local trade can also ask Adams Gas about becoming a stockist.

Frequently asked questions

What is OFN gas used for in air conditioning?

Oxygen-free nitrogen is used to pressure-test air conditioning and refrigeration pipework for leaks, purge moisture and debris from lines, and flow through copper pipework during brazing to prevent oxide scale forming inside the system.

Because nitrogen is inert and dry, it helps prepare a system without contaminating it before refrigerant is added.

What size nitrogen cylinder do I need for air conditioning testing?

This depends on how often you carry out testing.

Occasional users may only need a small disposable OFN bottle, such as a 0.95L or 2.2L cylinder.

Full-time installers usually choose a refillable 9.4L, 20L or 50L cylinder for a lower cost per test.

Busy workshops may be better suited to a manifolded cylinder pack.

Is oxygen-free nitrogen the same as normal nitrogen?

Oxygen-free nitrogen is a high-purity, dry grade of nitrogen with oxygen and moisture removed.

This purity matters for HVAC and refrigeration work because there is no oxygen to react with hot copper during brazing and no moisture to contaminate a sealed system.

For pressure testing and purging, engineers specifically use oxygen-free nitrogen.

Do I need a regulator for a nitrogen cylinder?

Yes. Nitrogen is stored at very high pressure, so a dedicated nitrogen regulator must be fitted to reduce it to a safe working pressure.

Adams Gas supplies a 300 bar single-stage nitrogen regulator with a twin-gauge design, suited to air conditioning testing and purging.

Can I buy nitrogen without paying cylinder rental?

Yes. Adams Gas supplies rent-free oxygen-free nitrogen.

Customers pay for the cylinder and the gas, with no ongoing rental charge and no long-term contract.

For engineers who only test a few times a week, removing rental charges can often save more over a year than the gas itself costs.