A BTU (British Thermal Unit) is a measure of energy, it often used to measure the heat dissipation of rackmountable equipment in equipment racks.
Galleon Systems NTS-4000 series NTP time servers are very low-power cool running devices. They consume approximatly 8 Watts of power.
Since 1 watt is equivalent to 3.412 BTU's, the nts-4000 series ntp time servers have a btu rating of 27.29 btu's.
This value can be utilised for calculating heat dissipation for the NTP time servers when mounted in equipment racks.