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In the United States and Canada, the R-value that describes the performance of thermal insulation is typically quoted in square foot degree Fahrenheit hours per British thermal unit (ft 2 ⋅°F⋅h/Btu). For one square foot of the insulation, one Btu per hour of heat flows across the insulator for each degree of temperature difference across it.
The therm (symbol, thm) is a non-SI unit of heat energy equal to 100,000 British thermal units (BTU), [1] and approximately 105 megajoules, 29.3 kilowatt-hours, 25,200 kilocalories and 25.2 thermies. One therm is the energy content of approximately 100 cubic feet (2.83 cubic metres) of natural gas at standard temperature and pressure. However ...
Common units for selling by energy content are joules or therms. One therm is equal to about 1,055 megajoules. Common units for selling by volume are cubic metre or cubic feet. Natural gas in the US is sold in therms or 100 cubic feet (100 ft 3). In Australia, natural gas is sold in cubic metres. One cubic metre contains about 38 megajoules.
This volume of natural gas has the same energy content as one US gallon of gasoline (based on lower heating values: 900 BTU/cu ft (9.3 kWh/m 3) of natural gas and 114,000 BTU/US gal (8.8 kWh/L) for gasoline). [22] One GGE of CNG pressurized at 2,400 psi (17 MPa) is 0.77 cubic feet (22 litres; 5.8 US gallons).
Units for other physical quantities are derived from this set as needed. In English Engineering Units, the pound-mass and the pound-force are distinct base units, and Newton's Second Law of Motion takes the form = where is the acceleration in ft/s 2 and g c = 32.174 lb·ft/(lbf·s 2).
The IEEE symbol for the cubic foot per second is ft 3 /s. [1] The following other abbreviations are also sometimes used: ft 3 /sec; cu ft/s; cfs or CFS; cusec; second-feet; The flow or discharge of rivers, i.e., the volume of water passing a location per unit of time, is commonly expressed in units of cubic feet per second or cubic metres per second.
Note that the m³ gas conversion factor takes into account a difference in the standard temperature base for measurement of gas volumes in metric and imperial units. The standard temperature for metric measurement is 15 degrees Celsius (i.e. 59 degrees Fahrenheit) while for English measurement the standard temperature is 60 °F.
Specific volume is a property of materials, defined as the number of cubic meters occupied by one kilogram of a particular substance. The standard unit is the meter cubed per kilogram (m 3 /kg or m 3 ·kg −1). Sometimes specific volume is expressed in terms of the number of cubic centimeters occupied by one gram of a substance.