Honeywell T991A1426 0/100F Prop. Temp. Control 5'Cap

The Honeywell T991A1426 is a proportional temperature controller for HVAC systems such as hydronic heating and cooling. It works by using a remote bulb that is either gas or liquid-filled to sense the temperature. A 5-foot capillary tube connects this bulb to the control unit. The liquid or gas expands or contracts in response to changes in the ambient temperature, informing the control unit. After interpreting the signal, the control unit modifies the output to maintain the user-specified temperature by varying the flow of hot or cold water. Compared to simple on/off switches, this proportional control guarantees smoother temperature adjustment and enhanced comfort. It may also increase energy efficiency by averting pointless cycles of heating or cooling.