Natural Gas Conversion: 5 Critical Points

What does a natural gas conversion actually involve?

A natural gas conversion moves a boiler or process heating system from gas oil (light fuel oil) or heavy fuel oil onto natural gas. It falls into two categories:

• Burner-only conversion: if the existing boiler is suitable for gas combustion, only the burner is replaced.
• Combined boiler and burner replacement: if the existing boiler is not suitable for gas combustion, or has reached the end of its economic life, both are replaced together.

Which category applies depends on the existing boiler's construction standard and certification — a decision that cannot be made without a site survey.

1. Authorisation: who is allowed to carry out the conversion?

This is the step most often overlooked, and the one with the most serious consequences if skipped. Gas installation and conversion work must be carried out only by installers holding the relevant accreditation from the gas distribution utility or national regulator, and unauthorised gas work is both illegal and genuinely dangerous in effectively every jurisdiction.

Turkey-specific note: in Türkiye, internal installation work (design, construction, maintenance and repair) requires a yetki belgesi (authorisation certificate) issued by the Energy Market Regulatory Authority (EPDK) and registered with the relevant gas distribution company (e.g. İGDAŞ, Başkentgaz, İzgaz). For industrial and large-consumption sites, the engineer producing the conversion design must additionally hold the Industrial and Large-Consumption Facility Natural Gas Conversion Engineer Qualification Certificate.

For comparison, gas work in Great Britain must be carried out by an engineer on the Gas Safe Register, the equivalent statutory scheme for installer competence.

Practical takeaway: when getting quotes, ask which distribution area the installer is authorised for, and — on industrial sites — ask to see the qualification certificate of the engineer producing the design. This is the only reliable way to avoid starting work that gets rejected later.

2. Design and utility approval

Conversion work cannot begin before a design has been approved by the gas distribution utility. The key points to establish at design stage:

• Condition of the existing plant room, including ventilation and flue routing
• Gas supply pressure — where a medium-pressure connection is taken, safe practice is not to bring more than around 1 bar into the building; regulation is designed down to the burner's actual operating pressure
• Pipe routing and sizing from the gas meter to the burner service valve

A conversion carried out without approval risks rejection at the gas turn-on stage and can create problems in a subsequent safety inspection.

3. Boiler-burner compatibility and EN 676 burner selection

Burner selection is driven by the boiler's capacity and construction — choosing "an equivalent kW burner" without checking compatibility is the most common specification error in the field. Points to check:

• The new burner must be EN 676 compliant and must sit within the boiler's capacity/back-pressure operating envelope.
• On existing certified cylindrical oil-fired boilers, conversion is only valid where a correctly-sized EN 676 gas burner is fitted and a conformity report is obtained from an accredited testing body confirming the conversion. This report is what makes the conversion technically valid, not just the physical burner swap.
• Mounting dimensions, combustion chamber depth and diffuser position must be adapted to the burner manufacturer's installation instructions.

4. Upgrading the plant room's safety equipment

A conversion affects more than the burner — it touches the plant room's safety equipment too:

• Explosion relief device: on cylindrical boilers, the explosion door/relief hatch must meet the applicable national standard (TS 10425 in Türkiye); its suitability for the new capacity is re-checked during conversion.
• Insulation: surfaces exposed to heat, such as the inner face of the front door, need insulation of adequate thickness.
• Gas train: safety shut-off valves (EN 161), pressure sensing devices (EN 1854) and, where fitted, the valve proving system (EN 1643) must be sized to the new burner's gas flow.
• Gas detection: a gas leak detector in the plant room is recommended as an additional layer of protection.

If any of these is skipped, the conversion can look complete — the burner fires — while the plant room remains deficient from a safety standpoint.

5. Commissioning: gas turn-on, initial combustion setting and flue gas measurement

The final, decisive stage is commissioning:

1. Gas turn-on is carried out by authorised personnel, following the distribution utility's procedure.
2. First firing and combustion setting is carried out with a calibrated flue gas analyser across every firing rate — O₂, CO₂, CO and flue gas temperature are measured and logged. See our guide to flue gas analysis and fuel savings for the measurement method.
3. Safety chain test — flame-loss cut-off time, and the air and gas pressure switch functions, are verified during commissioning.
4. EN 676 conformity record and the measurement results are kept on file — this record is used as a baseline for future scheduled maintenance and may be requested during an inspection.

Why convert: what does gas offer?

Natural gas burns considerably cleaner than gas oil or heavy fuel oil — sulphur content is negligible, which reduces both flue gas emissions and fouling of the heat exchanger and flue. Conversion also removes fuel-oil-specific operating costs entirely: the storage tank, pre-heating system and fuel delivery logistics. The precise cost comparison depends on current liquid fuel consumption, local gas and oil/heavy-oil prices, and the site's load profile, and should be calculated at design stage — quoting a generic percentage saving would be misleading.

3 common mistakes

1. Fitting an "equivalent" burner without a capacity calculation. A burner selected without checking the boiler's back pressure either fails to reach rated output or over-stresses the combustion chamber.
2. Starting work before the design is approved. Installation carried out without approval can be rejected at gas turn-on and require a costly rework.
3. Not reviewing the explosion relief hatch and insulation. Even where the burner changes, the suitability of the boiler's original safety equipment for gas combustion conditions must be checked separately.