Heat Value / Calorific Value
Different fuels contain different amounts of chemical energy. When a fuel is burnt, its chemical energy is transferred to other forms of energy. The heat value (a.k.a. calorific value) of a substance is used to indicate how much heat will be released by the process of combustion.
In a laboratory, the heat value is measured by burning a known amount of fuel at a constant pressure and temperature. The amount of heat transferred to a known amount of water (placed above the area of combustion) can be calculated by measuring the water’s change in temperature.
Heat values are usually given as either Higher Heat Values (HHV) or Lower Heat Values (LHV). LHV does not include the water’s latent heat energy due to vaporisation, HHV does, thus HHV is always equal to, or higher than, LHV.
The table below shows some common fuels and their associated heat values.
|
|
Imperial Units |
Metric Units |
||||
|
Fuel |
Approx. Heat Value (Btu/cu ft) |
Approx. Heat Value (Btu/gallon) |
Approx. Heat Value (Btu/lb) |
Approx. Heat Value (MJ/m3) |
Approx. Heat Value (MJ/litre) |
Approx. Heat Value (MJ/kg) |
|
Natural Gas |
1,000 |
|
22,000 |
37.0 |
|
50 |
|
Heavy Fuel Oil (HFO) |
|
147,000 |
18,000 |
|
38.0 |
41.0 |
|
Light Fuel Oil (LFO) |
|
151,000 |
19,000 |
|
39.0 |
42 |
|
Anthracite Coal |
|
|
14,000 |
|
|
31.0 |
|
Bituminous Coal |
|
|
13,000 |
|
|
29 |
Fuel Heat Values TableFuel Heat Values Table
Boiler Fuel Oils
Boiler fuel oils are rated #1 to #6. The higher the fuel number, the higher the heat value.
Example
- Kerosene is a grade #1 fuel oil with a heat value of approximately 134,000 Btu/gallon.
- Heavy fuel oil is a grade #4, #5 or #6 fuel oil, with a heat value of approximately 150,000 Btu/gallon.
A substance’s viscosity describes how easily a fluid flows under its own weight. For example, at 10°C, honey has a higher viscosity than water. Fuels with a higher viscosity (‘thicker’ fuels) tend to have a higher heat value than lower viscosity fuels (‘thinner’ fuels).
The below table is based upon information in the book ‘Handbook of Energy Engineering’ and provides further heat values of common fuels. Metric unit calculations were provided by the Cleave Books Unit Conversion Calculator, which can be found at the below link:
http://www.cleavebooks.co.uk/scol/index.ht
Additional Resources
https://en.wikipedia.org/wiki/Heat_of_combustion
https://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html
https://www.engineeringtoolbox.com/gross-net-heating-value-d_824.html