Cedar Ridge Recon Dual Fuel Blue Flame Heater - 20,000 BTU, Model# MD20TBU 20,000 Maximum BTU When Using Natural Gas or Propane Gas Heats Up To 750 Sq. Ft. Push Button Piezo Ignition System Economical: 99.9% efficient. No outside duct or chimney needed! Safety Assurance: O.D.S. (Oxygen Depletion Sensor) included with automatic shut-off