Reference data for common fuels in US and metric units. This comparative table brings together practical data for kiln planning and can support rigorous engineering calculations or practical estimates for fuel supply and key dimensions for chimney sizing, firebox and gas burner designs.
| Calorific value (energy released) | Stochio metric Air/ fuel ratio | Volume of air per MJ | Ignition temp | Adiabatic flame temp | Practical flame temp | Density at 15oC and 1 atmos | |
|---|---|---|---|---|---|---|---|
| Units | MJ/kg | m3/MJ | oC | oC | oC | kg/m3 | |
| Gases | |||||||
| Hydrogen | 120.2 | 2.38 | 0.02 | 500 | 2210 | 2040 | 0.090 |
| Butane | 45.3 | 31.00 | 0.68 | 405 | 1975 | 1970 | 2.590 |
| Propane | 46.3 | 23.80 | 0.51 | 455 | 1995 | 1960 | 1.970 |
| Methane | 48.7 | 9.50 | 0.20 | 580 | 1963 | 1950 | 0.714 |
| LPG | 46.6 | 23.80 | 0.51 | 450 | 1995 | 1980 | 1.970 |
| Natural gas | 48.7 | 9.50 | 0.20 | 580 | 1963 | 1950 | 0.714 |
| Biogas | 21.1 | 5.80 | 0.27 | 700 | 1850 | 1200 | 1.170 |
| Carbon monoxide | 12.6 | 2.38 | 0.19 | 609 | 2121 | 2120 | 1.250 |
| Air | n/a | n/a | n/a | n/a | n/a | n/a | 1.225 |
| Liquids and solids | |||||||
| Kerosene (Paraffin) | 45.0 | 12.1 | 0.22 | 210 | 2093 | 1970 | n/a |
| Charcoal | 32.0 | 11.5 | 0.29 | 349 | 1980 | 1150 | n/a |
| Coal | 26.1 | 6.9 | 0.32 | 454 | 2172 | 1100 | n/a |
| Wood, oak | 18.0 | 4.4 | 0.30 | 482 | 1980 | 1200 | n/a |
| Wood, pine | 19.0 | 4.4 | 0.28 | 427 | 1980 | 1200 | n/a |
| Calorific value (Energy released) | Stoichio metric Air/fuel ratio | Volume of air per 1000 BTU | Ignition temp | Adiabatic flame temp | Practical flame temp | Density at 60oF and 1 atm | |
|---|---|---|---|---|---|---|---|
| Units | BTU/lb | ft3 air/lb | ft3 | oF | oF | oF | lb/ft3 |
| GASES | |||||||
| Hydrogen | 51,644 | 2.38 | 0.046 | 932 | 3,998 | 3,704 | 0.006 |
| Butane | 19,482 | 31 | 35 | 761 | 3,533 | 3,518 | 0.162 |
| Propane | 19,911 | 23.8 | 25.9 | 851 | 3,623 | 3,572 | 0.123 |
| Methane | 20,944 | 9.5 | 9.78 | 1,076 | 3,581 | 3,542 | 0.045 |
| LPG | 20,040 | 23.8 | 25.7 | 842 | 3,623 | 3,596 | 0.123 |
| Natural gas | 20,944 | 9.5 | 9.78 | 1,076 | 3,581 | 3,542 | 0.045 |
| Biogas | 9,072 | 5.8 | 13.6 | 1,292 | 3,362 | 2,192 | 0.073 |
| Carbon monoxide | 5,411 | 2.38 | 7.28 | 1,128 | 3,860 | 3,848 | 0.078 |
| Air | n/a | n/a | n/a | n/a | n/a | n/a | 0.076 |
| LIQUIDS AND SOLIDS | |||||||
| Kerosene (Paraffin) | 19,332 | 12.1 | 11.6 | 410 | 3,803 | 3,518 | n/a |
| Charcoal | 13,745 | 11.5 | 15.3 | 660 | 3,596 | 2,102 | n/a |
| Coal | 11,207 | 6.9 | 20.6 | 849 | 3,951 | 2,012 | n/a |
| Wood, oak | 7,730 | 4.4 | 19.3 | 900 | 3,596 | 2,192 | n/a |
| Wood, pine | 8,159 | 4.4 | 17.9 | 801 | 3,596 | 2,192 | n/a |
Explanation of headings
Calorific value: The heat energy available per pound or kilogram of fuel. Technically known as the lower heating value, the data assumes that the latent heat in water vapour is not recovered.
Stoichiometric air-fuel ratio is the theoretical proportion of air needed for complete combustion; real burners require excess air to achieve a neutral or oxidising atmosphere.
Volume of air per BTU or MJ. This is the theoretical volume of air at the standard temperature and pressure that is needed to produce 1000BTU or 1 MJ of energy.
Ignition temperature: The temperature needed to light the fuel and sustain the flame.
Adiabatic flame temperature: This is the theoretical upper limit which would be achieved if the exact stoichiometric air-fuel ratio is achieved and no energy is consumed in heating the burner or firebox. This may be used in calculations and comparisons for pure gases.
Practical flame temperature is an approximation that can be helpful in the design of fireboxes and burners
Gas density: Thermal calculations have to be based on a stated standard temperature and pressure. These tables use 25oC and 1 atmosphere. Other sources may use 0oC and 1 atmosphere or the international IUPAC standard of 0oC and 1 bar, more widely used in chemical engineering.
Accuracy and reliability
Pure gas figures are rigorously based on molecular data and provide a chemically clean baseline.
Natural gas varies slightly, but is mainly methane. This means that figures for methane are accurate enough for practical applications like gas volume, jet size, and burner sizing.
Biogas is extremely variable due to its origin. Methane, the combustible component, is typically slightly more than 50% of the total gas volume. The table is based on 60% methane, 40% CO2.
Because of their natural origin, all solid fuels are very variable. The figures in the table are purely a guide to compare and contrast with the gases.
Applications of the data
- How much fuel is needed to produce the heat you need?
- Use for planning solid fuel storage or to determine the capacity of gas supply lines and piping.
- How much air is needed to burn the fuel?
- What size air intakes and flue exit are required?
- How must the firebox or burner be designed to mix the air with the fuel?
- Flame characteristics
- How easily can the flame be lit and sustained?
- Theoretical maximum temperature vs practical flame temperature.
- Flame temperature is only a guide for planning. It changes significantly with the position within the flame and depends on design of burner or hearth as well as draft and the fuel-air mix.
- Density of gas fuels
- Density is required for all practical gas calculations. In gas burners, the jet size determines the volume of gas being delivered, but the heat output is proportional to mass.
- At room temperature, butane is about 2.1 times as dense as air, and propane is 1.6 times the weight of the same volume of air. That means that leaked butane or propane can spread along the ground and collect in drains and basements forming an explosion risk.
Our separate article Solid fuel, Gas or Oil? explores some of the important differences in the physical nature of fuel and the implications for kiln design.
A new article will soon be published to cover the practical design of gas burners.
