Williams sells several models of heaters, for both residential and greenhouse use that run on natural gas. Alpine Home Air Products, ACF Greenhouses, eBay, HouseNeeds.com and the Home Depot retail various sizes of Williams units.
Thermal output sizes are available from 14,000 to 50,000 BTUs. All natural gas units are direct vent models with sealed combustion chambers, ensuring exhaust is vented outside of the structure. Williams heaters do not require electricity for operation, which lets them function during power outages. Optional blowers are available to increase heat circulation, but they do require electricity. Thermostats that can be mounted on the wall or heater cabinet are included with every heater. Users should not touch the unit during operation, because its external temperature can exceed 200 degrees Fahrenheit.