LS25 Separated Combustion Unit Heater

Lennox Commercial Heating 3


  • Heating capacities from 125,000-400,000 BTU/h
  • Designed for use in applications where the indoor environment may contain airborne contaminants, VOC’s or dust
  • Ideal for hard-to-heat applications where excessive humidity or negative pressure is a concern
  • Dimpled Tubular Heat Exchanger improves efficiency (82%) and increases durability
  • The hinged door allows easy access to components
  • Optional stainless steel heat exchangers provide superiror resistance to corrosion and oxidation
  • Sidewall venting eliminates roof penetrations
  • Self-diagnostic board with LED display improves troubleshooting efficiency and accuracy


  • Separated combustion units offer a robust heating solution for buildings with harsh indoor environments.
  • Fresh-air intake box can be rotated 180˚ degrees for increased installation flexibility in retrofit applications


  • Cage-nuts for all-thread installation on vertical units
  • Removable terminal block for line voltage and thermostats
  • Conveniently located gas connections
  • The hinged door allows easy access to all components
  • DSI control board has 11 diagnostic codes and remote LED fault detection diagnostics enabled