This unit is designed with a bulb and capillary assembly that automatically regulates the fuel flow to the Cata-Dyne™ heater. The sensing bulb is filled with temperature sensitive liquid, which responds to changes in temperature by expanding or contracting. This modulates the flow of fuel from 100% when heat is required to approximately 30% when the thermostat is satisfied. This unit is typically used to control building temperature for spot and space heating applications.