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Upgrade nowFuel Properties: Gas, LPG & Solid Fuel
Read through the material below, then test your understanding.
Module Lessons
Domestic Fuel Systems, Combustion & Flues
Fuel Properties: Gas, LPG & Solid Fuel
Fuel Properties: Oil & Low-Carbon Alternatives
Storing Oil, Coal & LPG
Storing Biomass & General Fuel Storage
Fuel Delivery & Distribution
Complete & Incomplete Combustion
Carbon Monoxide Poisoning
Combustion & Ventilation Air Requirements
Ventilation Categories & Calculations
Ventilation for Open-Flued & Room-Sealed Appliances
Flueless Appliance Ventilation Calculations
Types of Chimney & Flue Systems
Open Flues & Flexible Liners
Flue Terminals & Builder's Openings
Terminal Guards, Flue Blocks & Ridge Terminals
Room-Sealed (Balanced) Flues
Effective Height & Flue Routing
Flue Temperature, Condensation & Termination
Class 1 & Class 2 Flue Construction
Rigid & Flexible Metallic Flue Systems
Flue Testing Procedures
Flue Gas Analysis
Lesson Overview
Understanding the physical, chemical, and combustion properties of natural gas, LPG, and solid fuels is essential for correct appliance selection, safety, and regulatory compliance under Gas Safe and HETAS standards.
Learning Objectives
Identify the chemical compositions, specific gravities, and calorific values of natural gas, propane, and butane.
Compare the heat content, carbon percentage, and burning characteristics of commercial coal types, coke, and peat.
Recognise the legal registration requirements governing fuel systems under Gas Safe and HETAS.
Natural Gas Properties
Natural gas is a naturally occurring fossil fuel consisting primarily of methane (70–90%). Because it is colourless and odourless in its refined state, a waxy compound called mercaptan is added to provide a distinctive 'rotten egg' odour for leak detection.
The amount of energy stored in a fuel in its uncombusted state, released upon complete combustion, measured in MJ/m³ or MJ/kg.
Natural gas has a specific gravity of 0.6 to 0.8, meaning it is lighter than air and rises freely in well-ventilated spaces. Its calorific value ranges from 37.8 to 43 MJ/m³.
Liquefied Petroleum Gas (LPG)
LPG fuels are hydrocarbons extracted from oil wells and petroleum refining. The two primary commercial LPG variants used for heating and domestic services are commercial propane (C3H8) and commercial butane (C4H10).
| Property | Propane (C3H8) | Butane (C4H10) |
|---|---|---|
| Boiling Point | −42 °C | −4 °C |
| Specific Gravity (Air = 1.0) | 1.5 (heavier than air) | 2.0 (heavier than air) |
| Calorific Value (Volume) | 95.8 MJ/m³ | 111.4 MJ/m³ |
| Calorific Value (Mass) | 49.58 MJ/kg | 47.39 MJ/kg |
| Liquid Expansion Ratio | 1 litre liquid : 274 litres gas | 1 litre liquid : 274 litres gas |
Safety Hazard
Because LPG is heavier than air, escaping gas collects at low level in cellars, floor ducts, and drains. LPG storage vessels must never be installed near untrapped gullies.
Solid Fuel Classifications
Solid fuels vary widely by fossilisation age, moisture level, and carbon density. Higher carbon content yields higher heat output per kilogram.
| Fuel Type | Carbon Content (%) | Heat Content (kW/kg) | Key Characteristics |
|---|---|---|---|
| Anthracite | 86–97% | 10.0 kW/kg | Dense, shiny, highest heat output, burns cleanly. |
| Bituminous | 45–86% | 7.0–10.0 kW/kg | Smooth layers, common for power generation. |
| Sub-bituminous | 35–45% | 5.5–8.3 kW/kg | Higher moisture, lower heat than bituminous. |
| Lignite | 25–35% | 2.2–5.5 kW/kg | Crumbly brown coal, very high moisture content. |
| Coke | Very high | > Coal standard | Smokeless fuel produced in coke ovens at 1000 °C. |
| Peat | Low | Poor | Part-decayed plant matter from bogs, produces high ash. |
Statutory Registration Bodies
By law, operatives working on domestic natural gas or LPG installations must hold valid ACS competencies and be registered with Gas Safe. Solid fuel and biomass appliances are approved and governed under HETAS.
British Standard / Regulation
Natural gas appliances cannot be operated on LPG supplies without manufacturer-approved conversion kits, recalibration, or replacing injectors to accommodate differing operating pressures and flame characteristics.
Key Takeaways
Natural gas (predominantly methane) is lighter than air (SG 0.6–0.8) with a CV of 37.8–43 MJ/m³.
LPG (propane at −42 °C boiling point, butane at −4 °C) is heavier than air and expands 274 times from liquid to gas.
Anthracite provides the highest carbon content (86–97%) and greatest calorific output (10 kW/kg) among natural coals.
Gas and LPG work legally requires Gas Safe registration, while solid fuel installations are overseen by HETAS.
Next Steps
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