The total cooling capacity of a GL7 cooler is approximately 1 Joule per NTP litre of He3 used, at 300mK (although this assumes 100% condensation efficiency). The cooling capacity of a GL4 cooler is around 3.6 Joules per NTP litre, but only around 40% of the total charge is available for cooling during the run – the rest is consumed by the ‘base load’ of the cooler.