Fahrenheit, capitalization

Lowercase letters are also used for units derived from surnames when they appear in spelled-out form and do not follow a number. The abbreviated form, used as a unit after a number, is capitalized. Celsius and Fahrenheit are always capitalized because they refer to temperature scales (not actual units). 

Celsius and Fahrenheit are always capitalized. They are not themselves units they are the names of temperature scales. 

Another temperature scale, used in Canada and Europe and in the physical and life sciences in most countries, is the Celsius scale. In keeping with the metric system, which is based on powers of 10, the freezing and boiling points of water on the Celsius scale are assigned as 0 °C and 100. °C, respectively. On both the Fahrenheit and the Celsius scales, the unit of temperature is called a degree, and the symbol for it is followed by the capital letter representing the scale on which the units are measured °C or °F. 

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