Natural Gas vs LPG: Pressure Differences, Appliance Conversion, IGEM/UP/1C Requirements and Off-Grid Storage Safety

Quick Answer: Natural gas (methane) is supplied at 21 mbar operating pressure in the UK; LPG (propane) is supplied at 37 mbar for domestic use. Appliances are not interchangeable without a conversion — different injector sizes, regulator settings, and in some cases heat exchanger designs are required. LPG installation on domestic and commercial premises must follow IGEM/UP/1C (for LPG pipe sizing and installation) and the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). All LPG work must be carried out by Gas Safe Registered engineers registered for LPG.

Summary

Around 1.7 million UK homes use LPG as their primary heating fuel, mostly in rural areas off the national gas grid. LPG (Liquefied Petroleum Gas) is predominantly propane for most domestic installations, with butane used in portable applications (because butane does not vaporise below 0°C and is unsuitable for outdoor tanks in UK winters). The physical behaviour of LPG is fundamentally different from natural gas: it is heavier than air (unlike methane, which is lighter), meaning leaks accumulate at low levels and in pits, drains, and underfloor spaces — with serious explosion risk if ignition occurs.

From a tradesperson's perspective, the key distinction between natural gas and LPG work is that LPG appliances are factory-set for a specific gas type and must be formally converted (jet change, regulator change, or replacement of specific components) to operate on the other. A boiler purchased for natural gas cannot simply be connected to LPG supply without conversion — and vice versa. Most major manufacturers supply LPG conversion kits, but the conversion must be carried out by a Gas Safe Registered engineer registered for LPG work (registration category: LPG, not just NG).

The regulatory framework for LPG is broader than for natural gas. In addition to Gas Safe registration, LPG storage tanks and pipe installations must comply with IGEM/UP/1C, DSEAR 2002, and — for larger tanks — may require planning permission and Environment Agency notification.

Key Facts

• Natural gas operating pressure (domestic) — 21 mbar (U6 meter installation)
• LPG (propane) operating pressure (domestic) — 37 mbar (after first-stage regulator at tank)
• LPG calorific value — propane: approximately 93.2 MJ/m³; butane: approximately 121.8 MJ/m³; higher than natural gas (38.7 MJ/m³)
• Wobbe Index — determines interchangeability; natural gas ~52.9 MJ/m³; propane ~81.3 MJ/m³ — not interchangeable
• LPG density — propane vapour is approximately 1.5× denser than air; natural gas (methane) is approximately 0.55× air density
• LPG tank sizes (domestic) — 47kg cylinders; 250kg to 1,050 litres bulk tanks for permanent installations
• Minimum tank siting distance — 1,000 litre tank: 3m from building, 2.5m from non-fixed ignition source; 250–999 litre: 1m from building (LP Gas Association Codes of Practice)
• Gas Safe LPG registration — required for all LPG installation work; separate registration category from natural gas
• IGEM/UP/1C — Institute of Gas Engineers and Managers standard for domestic and commercial LPG pipe installation
• Appliance conversion — requires manufacturer-approved conversion kit; injector change and regulator resetting mandatory
• Injector size (jets) — LPG jets are smaller than natural gas jets (higher CV per m³); using wrong jets causes incorrect combustion
• DSEAR 2002 — Dangerous Substances and Explosive Atmospheres Regulations; applies to LPG storage and use
• Bulk tank refill — bulk LPG tanks are owned by the gas supplier (Calor, Flogas, etc.); they must not be filled by a different supplier without tank ownership transfer
• Vapour pressure — propane vapour pressure increases rapidly with temperature; tanks should not be sited in direct sunlight or enclosed structures

Quick Reference Table

Detailed Guidance

Appliance Conversion: Natural Gas to LPG

Converting an appliance from natural gas to LPG requires:

1. Manufacturer conversion kit — obtain the correct kit for the specific appliance model. Kits typically include replacement injectors (jets), a regulator or regulator adjustment guide, updated data badge, and instructions.

2. Injector replacement — injectors (jets) meter the gas flow. LPG has a higher calorific value per cubic metre but is supplied at higher pressure and different flow characteristics. LPG injectors have a smaller orifice than natural gas injectors for the same heat output. Using the wrong injectors results in incorrect combustion (sooting, incomplete combustion, CO production).

3. Regulator setting — some appliances have an adjustable gas valve that requires resetting from 20 mbar to 37 mbar; others require a different regulator. This must be set using a calibrated manometer.

4. Flue gas analysis — after conversion, analyse flue gases with a calibrated flue gas analyser. CO/CO₂ ratio must be within manufacturer's specification. Any reading above 10ppm CO at flue outlet warrants further investigation.

5. Data badge update — update the appliance data badge to show the new gas type.

6. Gas Safe certification — issue a Gas Safe completion certificate noting the conversion. Record the appliance serial number, conversion kit reference, and gas type.

Conversion in the other direction (LPG to natural gas) follows the same process in reverse.

LPG Pipework Installation (IGEM/UP/1C)

IGEM/UP/1C covers the design and installation of LPG distribution pipe installations from the storage vessel to the appliance. Key requirements:

Pipe sizing:

• Use the flow rate (kW or BTU/hr) at each appliance to calculate pipe diameter
• LPG distribution pressure is 37 mbar; pressure drop allowance is typically 2.5 mbar maximum over the installation
• IGEM/UP/1C Table 1 gives maximum flow rates for steel, copper, and PE pipe at given diameters and lengths

Pipe materials:

• Copper (light gauge to BS EN 1057) is the most common material indoors
• PE (polyethylene, BS EN 12201) for underground pipework from tank to building
• Steel (medium weight) for commercial/industrial; galvanised steel must not be used for LPG (methane is inert to zinc, but LPG can strip residues from galvanised surfaces and block injectors)

Pipe identification:

• LPG pipework must be identified with yellow label tape at intervals and at all connections (yellow = gas)
• Mark on any drawings and on the installation record

Pressure testing:

• Test at 1.5× working pressure minimum (55 mbar for a 37 mbar system)
• Use dry nitrogen or the gas itself; water is not used for gas system testing
• Record test pressure, duration, and result

LPG Storage Safety (DSEAR)

LPG is a flammable substance. DSEAR 2002 requires any workplace storing or using LPG to carry out a risk assessment for explosive atmospheres. For domestic and small commercial installations:

Tank siting (LP Gas Association Codes of Practice Part 1):

Key points:

• Tanks must not be sited below ground level (vapour heavier than air — leak would flow into underground spaces)
• Tanks in enclosed spaces (sheds, garages) are not permitted
• Tanks must have a pressure relief valve (PRV) with clear discharge path away from ignition sources
• Regulator outlet must be piped away from air bricks, vents, and window openings

Ventilation in enclosures with LPG appliances:

• LPG appliances in cellars or basements are generally prohibited without specialist design (leak accumulation risk)
• All rooms with LPG appliances must have low-level ventilation (air inlet at floor level) in addition to normal appliance ventilation requirements

Off-Grid LPG vs Oil

For properties that cannot connect to the gas grid, LPG and oil are the two main fuel options. Key differences:

Frequently Asked Questions

Can I use the same Gas Safe registration for natural gas and LPG work?

No. LPG is a separate competency category on the Gas Safe Register. Engineers must hold separate registration for LPG work. Check your registration certificate — it will list the categories you are approved for. Taking on LPG work without the relevant registration is a criminal offence under the Gas Safety (Installation and Use) Regulations 1998.

Why does LPG smell stronger than natural gas?

Both natural gas and LPG are odorised with mercaptans (typically ethyl mercaptan or THT) because the gases are naturally odourless. The smell is added by the gas supplier before distribution. The perceived intensity varies by person and by gas type but the odorant concentration is calibrated to be detectable at approximately 20% of the Lower Explosive Limit (LEL). If a customer says LPG smells stronger, it may be that a very small leak is present — LPG accumulates at floor level and the smell can become more concentrated in poorly ventilated spaces.

Is LPG being phased out in the UK?

There is no current UK government plan to ban LPG, unlike the trajectory for natural gas boilers (new gas boiler sales banned in new builds from 2025 and phased out nationally from 2035). LPG is a fossil fuel and does not qualify for government incentive schemes (BUS, etc.). Many LPG customers are considering switching to heat pumps or biomass as the LPG equipment reaches end of life — this is a growing market opportunity for installers.

What do I do if an LPG tank is overfilled?

An overfilled LPG tank can release liquid (not vapour) through the PRV, which rapidly vaporises, creating a flammable cloud. If you suspect overfilling (tank showing more than 85% capacity, frost on the tank, PRV discharging):

1. Remove ignition sources and evacuate the area
2. Contact the LPG supplier immediately
3. Do not attempt to operate any appliances
4. Do not attempt to vent the tank yourself

Regulations & Standards

• IGEM/UP/1C — Institute of Gas Engineers and Managers; LP Gas installation in domestic premises; pipe sizing and installation requirements

• Gas Safety (Installation and Use) Regulations 1998 — statutory requirement for Gas Safe registration for all gas work including LPG

• DSEAR 2002 — Dangerous Substances and Explosive Atmospheres Regulations; risk assessment and controls for LPG storage

• LP Gas Association Codes of Practice — industry guidance on LPG tank siting, installation, and safety

• Building Regulations Part J — combustion appliances; applies to LPG boilers and fires

• Pressure Systems Safety Regulations 2000 — applicable to LPG bulk storage systems above a threshold pressure and volume

• LP Gas Association — UK LPG industry body; Codes of Practice available for download

• Gas Safe Register — competency categories, registration guidance

• IGEM — IGEM/UP/1C standard and other installation guidance

• HSE LPG Guidance — DSEAR compliance, risk assessment guidance

• gas appliance servicing — servicing LPG appliances: annual check scope

• oil boiler installation — oil heating as an alternative off-grid fuel

• boiler selection — choosing boiler type for off-grid properties

• fire safety site — explosive atmospheres and hot works near LPG