About Gas Fired Unit Heaters ABOUT GAS FIRED UNIT HEATERS U.S. Global Resources offers a wide variety of Modine and Siebring natural gas and propane (LPG) fired unit heaters. The propane (LPG) and gas fired unit heaters are one of the most popular heaters used in greenhouses, barns, dairies and other animal confinement buildings. For barns and dairies where natural gas or propane is not available we have oil fired heaters as well as waste oil heaters. Natural gas and propane (LPG) fired unit heaters are available in stainless steel and aluminum. Aluminum gas fired unit heaters are the most popular because they are more economical. The aluminized heat exchanger is tube type and comes on all of our propane and natural gas unit heaters. Our unit heaters have direct spark ignition. Some natural and propane (LPG) heaters are available with power exhaust. Our Modine, Siebring unit heaters have been proven during years of thousands of hours of the toughest winter conditions. All gas fired and propane unit heaters must be vented. Vents can be shipped with the unit heater or purchased locally whether you are using the Modine or Siebring natural gas or propane (LPG) heaters. Adjusted louvers available on all Siebring and Modine unit heaters. As these units are air delivery heat systems, they can be used with fanjet or multiple units to cover large greenhouse areas. We offer greenhouse heaters of all types, natural gas, propane, oil, waste oil, steam or hot water units. All available from warehouses stocked with Modine and Siebring unit heaters. These units are also extremely popular for barns, dairy operations and animal confinement buildings of all types. When using these units for greenhouse, poultry, animal confinement, dairies and barns, proper ventilation is essential, particularly when used in barns, dairies, etc, where structures are very tightly closed during the winter. The barn, dairy, poultry and animal buildings are excellent for the air moving natural and propane gas (LPG) unit heaters.