By precisely matching air and gas proportions, SunTwin 2-stage high-intensity Series achieves optimal combustion in both operating stages. All fuel is consumed leaving no trace of burnable agent or residual oxygen. IR heater eliminates overheating to provide soft comfortable heat. Models are available with 50,000-200,000 Btu/hr for natural gas; 45,000-160,000 Btu/hr for LP/propane. Digital 2-stage thermostat, 24 V, reduces on/off cycles to extend product life.