HFT40009Z-01 Thermostatic mixing valve
Do you know what is a mixing valve in the underfloor heating system? Let’s learn the function first. Basically, underfloor heating mixing valves work by mixing hot water with cold water to regulate the temperature of the water flowing through the underfloor pipes. This crucial component in a hydronic/wet underfloor heating system draws hot water from the boiler and cold water from the return loop. When these mixing valves function properly, the system will provide stable heat.
Stable heat, maintained at the ideal temperature you set in advance, ensures comfort. The room will not become too hot, and the underfloor heating mixing valves will also prevent damage to floors and other materials.
Contents
Main Function of Underfloor Heating Mixing Valves
The main function of underfloor heating mixing valves is to control the flow water temperature entering the underfloor heating system. The supply water temperature is typically between 30–45°C, depending on system design. Temperatures in this range help prevent damage to floor materials while ensuring efficient heating.
Efficiency in the system means that mixing valves effectively maintain a consistent flow temperature by mixing hot water with cooler return water. As the overall efficiency of the heating system increases, energy consumption gradually decreases.
Mixing valves also prevent the pipes from overheating. When the temperature in the pipes rises too high, the risk of damage increases. This can lead to leaks, pipe deformation, or long-term damage to the underfloor heating system.
Types of Underfloor Heating Mixing Valves (by Control Method)
Many modern underfloor heating mixing valves allow for manual or automatic temperature adjustment. Some feature thermostatic control, while others can be set to a specific temperature based on the system design.
It’s important to be observant and well-informed when choosing the right type of underfloor heating mixing valve for your home system. Below are three common types of mixing valves available on the market:
| Type | Temperature Control | Automation Level | Typical Application |
|---|---|---|---|
| Thermostatic Mixing Valve (TMV) | Automatic, self-regulating | Medium | Residential underfloor heating |
| Manual Mixing Valve | Manual adjustment | Low | Small or basic systems |
| Motorized Mixing Valve | Controller-driven | High | Large homes, commercial systems |
TMV (Thermostatic Mixing Valve)
The thermostatic mixing valve (TMV) automatically adjusts the mixture of hot and cold water. This is essential for maintaining the temperature you have previously set within the system.
Manual Mixing Valve
As the name suggests, this valve requires the user to adjust it manually. You can turn the knob or press a button to control the mixture of hot and cold water. However, because they do not respond automatically to temperature changes, they are not common in modern underfloor heating installations.
Motorized Valve
The motorized or electronic valve operates through a programming process. As a user, you can control it remotely, adjusting the mixing based on your heating needs. This type of valve is often used in larger residential or commercial underfloor heating systems where more precise and dynamic temperature control is needed.
Motorized (electronically controlled) thermostatic mixing valve
Types of Underfloor Heating Mixing Valves (by Valve Configuration)
Mixing valves can also be classified by their internal flow design and number of ports.
| Valve Configuration | Number of Ports | System Size | Typical Use |
|---|---|---|---|
| 3-Way Mixing Valve | 3 | Small to medium | Residential underfloor heating |
| 4-Way Mixing Valve | 4 | Medium to large | Commercial or complex systems |
3-Way Mixing Valve
The 3-way mixing valve is the most commonly used configuration in underfloor heating systems. It has three ports: a hot water inlet, a return water inlet, and a mixed water outlet.
3-way mixing valves are suitable for most residential underfloor heating applications and can be thermostatic, manual, or motorized.
4-Way Mixing Valve
4-way mixing valves are used in larger or more complex heating systems. In addition to mixing hot and return water, they help stabilize circulation and protect the heat source from sudden temperature changes.
This type of valve is more commonly found in commercial or industrial underfloor heating systems rather than typical residential installations.
Installing Underfloor Heating Mixing Valves
Installing underfloor heating mixing valves requires precision and attention to detail to ensure proper operation, which in turn increases system efficiency.
You can install underfloor heating mixing valves yourself if you are familiar with the general steps outlined in the guide and have the necessary plumbing expertise. However, if you’re unsure, especially when dealing with more complex or extensive installations, it’s best to call a professional plumber.
Tools and Materials You’ll Need
Start by preparing the main tool: the underfloor heating mixing valve. You can choose from manual, motorized, or TMV (thermostatic) series. Be sure to source the valve from a reputable manufacturer known for producing innovative products that will enhance your system’s energy efficiency.
Additionally, you’ll need the following tools and materials:
- Pipe cutter.
- Plumber’s tape (PTFE).
- Flow and return pipe connectors.
- Screwdriver (for tightening the valve in place).
- Pipe insulation.
- Thermometer (to check the water temperature).
Installation Steps
HFT33003Z-01 Thermostatic mixing valve
Always begin by turning off the heating and water supply systems before installing underfloor heating mixing valves. Then, drain the system to prevent any spills. Follow these steps to ensure proper installation:
Valve Placement Planning
Determine the location for the mixing valve. The placement is usually between the heat source (such as a boiler or heat pump) and the supply manifold of the underfloor heating system.
Install the mixing valve on the flow pipe to regulate the water temperature before it enters the underfloor system. Ensure the valve is easily accessible for future adjustments and maintenance.
Pipe Cutting
Install the mixing valve where the hot supply, cold return, and mixed flow lines meet. Use a pipe cutter to ensure clean, symmetrical cuts. Neat pipe cuts will help ensure proper sealing when adding connectors.
Valve Installation
Install the mixing valve at the point where the hot water supply, cooler return water, and mixed flow lines meet. This is typically between the heat source (e.g., boiler or heat pump) and the manifold. Use the appropriate connectors, which may include compression fittings, press fittings, or soldering, depending on your system. Make sure to use PTFE tape on the connector threads to create a watertight seal. Some valves may already have compression fittings installed, while others will require you to add them.
Installing a Temperature Sensor
Some mixing valves require a temperature sensor to monitor the incoming water temperature. If so, install the sensor in the recommended location, often on the return pipe, as advised by the manufacturer.
Connecting the Return Line
Connect the return pipe from the underfloor heating system to the return port of the mixing valve. This ensures that the return water mixes with the hotter water from the boiler before being delivered to the underfloor system.
Set the Temperature
For thermostatic mixing valves, set the temperature control to the desired level. Ideally, the temperature should be in the range of 35-45°C for underfloor heating systems. For manual valves, adjust the valve until the ideal temperature is reached. Use an internal thermometer to monitor this.
Check for Leaks
Once the mixing valve is good in installation, slowly turn on the water supply and check for leaks around the connections. Tighten any loose connections if necessary.
It is important to address leaks before operating the system. Once you’re confident that there are no leaks, reconnect the system and turn it on.
Final Monitoring
Monitor the valve’s operation to ensure it is working correctly. After the system reaches the correct temperature, you should begin to feel warmth coming from the floor.
Conclusion
With the right mixing valve and a careful installation, your underfloor heating system can run more smoothly, safely, and efficiently. It’s a small part that makes a big difference, we help you to keep your floors warm and your energy bills in check. Consult with us!
Last updated: 2 February 2026 — technical content reviewed and updated for accuracy