Mixing unit Termojet for underfloor heating manifold TJ-MU-25

The Termojet TJ-MU-25 pump-mixing unit is a ready-to-use hydraulic assembly for reducing the heat-transfer fluid temperature from a boiler or heat pump to the safe level of 20–60°C required for an underfloor heating system. The thermostatic head with a remote sensor automatically regulates the proportion of cold return fluid blended into the hot supply — the floor circuits always receive heat-transfer fluid at the required temperature without the risk of overheating the screed.

Technical Specifications

Operating Principle

The boiler or heat pump heats the fluid to its working temperature — often 60–80°C for a boiler or 40–50°C for a heat pump. Underfloor heating pipework is rated for a much lower temperature: optimal supply 30–45°C, maximum permissible — 55°C. The pump-mixing unit solves this: the circulation pump (selected separately) ensures constant circulation in the floor circuit, while the three-way valve controlled by the thermostatic head smoothly blends cooled return with the hot supply. The remote sensor monitors temperature directly at the supply point — the valve responds instantly regardless of the boiler operating mode.

Where It Is Used

• House with a gas or solid-fuel boiler. The boiler is set to 70–80°C for the radiator circuit, and the TJ-MU-25 unit reduces the temperature to a safe 35–45°C for the floor circuit — both circuits operate in parallel at their own temperatures.
• Radiators + underfloor heating system. A single boiler serves both types of heating: radiators at full supply temperature, floor heating through the mixing unit.
• Screed protection during initial warm-up. During the first system start-up or after renovation, the unit prevents excessively hot fluid from entering and cracking the concrete screed.
• Zone control. Paired with a manifold with flow meters and M30×1.5 thermal actuators, the unit provides per-circuit temperature regulation in each room.

Advantages of the Termojet TJ-MU-25 Unit

• Ready assembly — the valve, thermostatic head and sensor are pre-mounted; only the circulation pump has to be selected.
• Thermostatic head with remote sensor — accurate temperature measurement at the supply point, not inside the unit body.
• Wide range of 20–60°C — suitable for both low-temperature heat pumps and gas boilers with high supply temperatures.
• Protection of floor circuits and screed from overheating — safe operation without constant supervision.
• Compatible with any Termojet underfloor heating manifold with a 1" connection.

Underfloor Heating and Heat Pump

A heat pump achieves its maximum efficiency coefficient (COP 4–5) precisely at a low heat-transfer fluid temperature — 35–45°C. Underfloor heating is the ideal consumer for a heat pump: exactly such a temperature is sufficient for it. When using a heat pump, the pump-mixing unit often acts as a hydraulic distributor between the primary and secondary circuits — even when temperature reduction is not required, the unit ensures stable circulation in the floor circuit. More about compatible solutions — on the Termojet heat pumps website.

Frequently Asked Questions

Is a mixing unit needed with a heat pump?
With a heat pump the system is already low-temperature — supply 35–50°C. If the heat pump is the sole heat source and there is a single underfloor circuit, the unit may not be required. But if there are multiple circuits or a combination of heat pump and boiler (bivalent scheme) — the TJ-MU-25 unit separates the hydraulics and protects the floor circuits from peak boiler temperatures.

How many circuits does the TJ-MU-25 unit serve?
The unit connects to a manifold that already distributes the fluid across circuits. The number of circuits is determined by the manifold: from 2 to 15 outlets depending on the chosen model. The TJ-MU-25 serves the entire manifold as a single secondary connection circuit.

The circulation pump is not included in the scope of delivery — it is selected separately.