Adjust heat output

Question

Have Reddy Heater propane model RLP35 35000 BTU output. Can I add anything to this unit to cut down on the heat needed? Example get a area warm now just want to maintain it not have the heater blasting. I see other units have variable BTU outputs. How is this done? By fan speed or a combination of fan speed and gas output? I think a part from another similar unit could be added. Has anyone done this or knows how? If anyone can help let me know. Someone out there has done this or knows how.. Thanks a lot everyone,