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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.
U = Overall heat transfer coefficient in Btu/(ft2-hr-deg F) A = Area in square feet T1 = outdoor temperature in degrees F T2 = indoor temperature in degrees F For heat gains due to people, equipment (hooded and unhooded), and lighting
Although the concept of U-value (or U-factor) is universal, U-values can be expressed in different units. In most countries, U-value is expressed in SI units, as watts per square metre-kelvin: W/(m 2 ⋅K) In the United States, U-value is expressed as British thermal units (Btu) per hour-square feet-degrees Fahrenheit: Btu/(h⋅ft 2 ⋅°F)
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On average, an air conditioning unit needs about 20 BTUs per square foot of space to keep things cool, said McKeon. ... From 250 up to 350 square feet: 7,000 to 8,000 BTUs. From 350 up to 450 ...
kelvin square-metre per watt (K⋅m 2 /W or, equally, °C⋅m 2 /W), whereas the I-P (inch-pound) unit is degree Fahrenheit square-foot hour per British thermal unit (°F⋅ft 2 ⋅h/BTU). [13] For R-values there is no difference between U.S. and Imperial units, so the same I-P unit is used in both.
Measured in square feet, the reference standard for EDR is the mattress radiator [1] invented by Stephen J. Gold in the mid 19th century. One square foot of EDR is able to liberate 240 BTU per hour when surrounded by 70 °F (21 °C) air and filled with steam of approximately 215 °F (102 °C) temperature and 1 psi of pressure.
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