Kelvin temperature from heat attribute When simulating fire, the heat attribute gives a scalar representing the heat, but the blackbody node, which converts a temperature to a color requires the heat to be specified in Kelvins, and the heat scalar is not in Kelvin.

My question is, therefor if there is an unambiguous way of converting the heat scalar to kelvin temperature if I already know what type of combustion this is (ie. is it a flame of a candle or burning barrel of oil)
Yes. Multiply it by 1000.

Temperature
Gives a scalar defining the temperature of the volume. Values in the range 0..1 map to 0..1000 kelvin. This may be used to render physically-based fire with the Blackbody or Principled Volume shaders. All three outputs are the same.

From https://docs.blender.org/manual/en/dev/render/cycles/nodes/types/input/attribute.html
So the attribute node gives the temperature in Kelvins in the range [0,1000] mapped linearly to the range [0,1]. To change it back, you can simply multiply it by 1000.
Interestingly, what seems to refer explicitly to &quot;Temperature&quot; is actually referencing the &quot;heat&quot; attribute. using &quot;temperature&quot; in the attribute node simply returns 0, as if it were any undefined token.