HERZ MINI underfloor heating return temperature limiter set 1/2", straight, 25–60 °C, 1920123

HERZ 1920123 is a straight return-temperature limiter set designed for temperature control of a small hydronic underfloor-heating circuit. It automatically limits the temperature of the returning heating medium and therefore helps prevent excessively high temperatures in the floor-heating circuit. It is particularly suitable for individual small floor-heating zones such as bathrooms, kitchens and entrance areas.

The set consists of the HERZ MINI return-temperature limiter 1 9201 00 and the straight HERZ TS-90 thermostatic valve 1 7733 81. The DN15 valve features an R 1/2" connection with cone seal and a G 3/4" male Eurocone pipe connection for suitable compression adapters.

The MINI limiter operates as a self-acting proportional controller. Heat from the returning water is transferred through the valve body to the temperature sensor. If the return temperature rises above the selected value, the valve progressively closes and reduces the flow through the floor-heating circuit. As the return temperature falls, the valve opens again.

The adjustment range is 25–60 °C. The scale approximately corresponds to 25 °C at position 1, 35 °C at position 2, 45 °C at position 3, 55 °C at position 4 and 60 °C at position 5. The selected setting range can be limited or locked using HERZ stop pins 1 9551 02, which are ordered separately.

This is not a conventional room-temperature thermostatic head. The HERZ MINI head regulates the temperature of the return heating medium, rather than directly sensing room-air temperature.

The straight HERZ TS-90 valve does not feature integrated pre-setting. The DN15 valve has a Kvs value of 1.10 m³/h. Suitable G 3/4 compression adapters for copper, steel or plastic pipe must be selected according to the pipe dimensions and ordered separately.

The valve/limiter assembly has a maximum operating temperature of 110 °C and maximum operating pressure of 10 bar. For the RTB underfloor-heating application, HERZ specifies a maximum heating flow temperature of 70 °C, maximum differential pressure of 0.2 bar, a recommended limiter setting of maximum 55 °C and a recommended maximum underfloor-heating operating temperature of approximately 35 °C.

HERZ indicates this type of RTB solution for relatively small individual floor-heating circuits, with a room heating load of approximately 1000 W and a maximum floor-heating pipe length of around 20 m. Actual design limits depend on pipe size, spacing, floor construction and heat demand.

Technical information