Honeywell Heat Detection Thermostats, 2455RA Series, 2455RA-04170929, Switch Type SPST, Automatic Reset, Close on Rise, Contact Type Silver Alloy, Fire Alarm, 3A, B237, T106, Operating Temperature 47 °C to 107 °C [117 °F to 225 °F], Open Temperature 55 °C [131 °F], Close Temperature 77 °C [170.6 °F], Open Tolerance 4 °C [7.2 °F], Close Tolerance 4 °C [7.2 °F]