Johnws. The S.I unit for heat is the Joule (J) it takes 4,186 J of energy to raise the temp of 1 litre (= 1 kg) of water through 1degree C this is called the specific heat capacity of water.
Heat energy =mass specific heat capacity temp rise
H.e (kg) = mass (kg)x 4.186 (t2 -t1)deg c
Johnws, you need to know the initial temp to calculate.
the temp dif in a pressure situation is aprox 1deg f / 550ft