NuTemp's inventory of direct-fired heaters operate on either propane or natural gas. Sizes range from 400,000 to 4,500,000 BTUs. Our new line of make-up air heaters offers the latest in control and safety technology. Modulating burners and high capacity fans save a bundle on fuel costs compared to standard "prop fan" heaters. By constantly pulling in fresh air, warming it with clean burning propane or natural gas, our make up air heaters create a warm and dry environment for a building under construction.