What Is a Thermostatic Radiator Valve? Savings and Comfort Guide

How Does a Thermostatic Radiator Valve Work?

The valve has two parts: the valve body, fitted to the radiator’s inlet connection, and the thermostatic head mounted on it. The sensing element inside the head (liquid, gas or wax filled) expands as the room warms up and pushes the valve spindle to throttle the water flow; as the room cools it contracts and the valve opens again. Mechanical heads do this without batteries or electricity.

A thermostatic valve is different from an ordinary radiator valve that is opened and closed by hand. An ordinary valve stays in the position you leave it and does not sense the room temperature.

What Does a Thermostatic Radiator Valve Do?

• It lets you set the temperature of each room separately.
• It prevents rooms that are sunny, crowded or have another heat source from overheating.
• It allows you to keep unused rooms at a lower temperature.
• It helps save fuel in combi boiler and central systems by reducing unnecessary heating.

How Much Does a Thermostatic Valve Save?

The amount saved cannot be expressed as a single rate; it depends on the building insulation, how the rooms are used, previous habits and whether the system is balanced. The savings come from the valve keeping the room at the desired temperature and from not heating unused or sunny rooms unnecessarily. If you leave all heads at the highest setting, the valve behaves like an ordinary radiator valve and the savings effect is reduced.

In centrally heated buildings, whether these savings show up on the apartment’s bill depends on heating costs being allocated by consumption. The apartment’s share is measured with a heat meter or heat cost allocator; for how allocation works, see our Central Heating Cost Allocation article.

Types of Thermostatic Radiator Valves

By head type

• Mechanical head: Needs no batteries or electricity; operated with a stepped setting knob.
• Electronic (smart) head: Battery powered. Depending on the model, it offers time programs, digital temperature setting, a mobile app or wireless connectivity; for example, it can lower the temperature automatically at night or when you are away.
• Head with remote sensor: Used when the valve is behind a curtain, furniture or a radiator cover, to sense the temperature at an open spot in the room.

By valve body type

• Angle and straight type: Chosen according to the direction from which the pipe reaches the radiator. If the pipe comes up vertically from the floor, an angle type is usually used; if it comes horizontally in line with the radiator connection, a straight type is used.
• Axial type: Offers a different connection direction so that the head can sit horizontally.
• For compact (valve-integrated) radiators: In some bottom-connected panel radiators the valve body is inside the radiator; a matching thermostatic head is used, together with an H-type connection piece for the bottom connection.
• Models with PEX connection: Supplied with a union suitable for plastic (PEX) pipes.

The connection between head and body may vary by brand; when buying a head from a different brand, check its compatibility with the body. For models, see our thermostatic radiator valves category.

How to Set a Thermostatic Valve

Heads usually have numbers from 1 to 5 and a frost protection symbol (snowflake). Which temperature each number corresponds to varies by brand; on many models the middle setting (3) is about 20 °C. The exact values are given in the product’s instructions.

The values below can serve as a starting point; adjust up or down by one step as needed:

After changing the setting, the room takes time to settle at the new temperature; instead of changing the setting frequently, wait a few hours and assess the result. Turning the head to the highest setting does not heat the room faster; it only raises the target temperature.

How to Fit a Thermostatic Valve

Replacing the valve body involves working on the system water, so it is advisable to have it done by an installer. The general sequence is:

1. The boiler or heating is switched off and the radiator is left to cool.
2. The radiator’s inlet valve and the lockshield valve on the return are closed; if these valves are missing or leaking, the system is drained.
3. The water in the radiator is drained and the old valve is removed.
4. The new valve body is fitted using suitable sealing material on the threads.
5. The valves are opened or the system is refilled; the radiator is bled and checked for leaks.
6. The thermostatic head is fitted to the body and set.

To bleed the radiator, see our How to Bleed a Radiator guide. During installation, pay particular attention to two positions:

• The head should be horizontal: If the head is vertical, right above the warm air rising from the pipe, it senses a higher room temperature than the actual one and throttles the valve too early.
• The front of the head should be clear: A curtain, furniture or radiator cover traps warm air around the head; the valve closes before the room has warmed up. In this case a head with a remote sensor can be used.

Use with a Boiler and Room Thermostat

• It is recommended not to fit a thermostatic valve to the radiator in the room with the room thermostat, or to leave that valve fully open. If two controls conflict in the same room, the valve throttles the room before the thermostat does; since the thermostat cannot reach its target temperature, it may run the boiler unnecessarily.
• If all radiators have thermostatic valves and they all throttle at the same time, the pump needs a path (bypass) to circulate the water. Find out from the manual or the service technician whether your combi boiler has an internal bypass.

Thermostatic Valves in Central Systems

In centrally heated buildings, thermostatic valves provide room-by-room temperature control inside the apartment. When used together with consumption-based allocation using heat meters or heat cost allocators, how the apartment uses heat is also reflected in its bill. For reading heat cost allocator values, see our How to Read a Heat Cost Allocator guide.

The hydraulic balance of the system is also important for the valves to work properly; in an unbalanced system some radiators may not heat enough even with the valve open. For the effect of shutting radiators off completely in a central system, see our 15 °C Minimum Heating Limit article.

Common Mistakes

• Setting all heads to the same level: Rooms differ in use and sun exposure; each room should be set according to its own needs.
• Shutting an unused room off completely: A room that cools down completely is at greater risk of condensation and mold. A low setting or the frost protection position is better.
• Covering the head with a curtain or furniture: The valve senses the room temperature incorrectly.
• Throttling the valve in the room with the room thermostat: The thermostat and the valve interfere with each other.
• Leaving the valve closed all summer: Outside the heating season, leaving the head at the highest setting, i.e. fully open, helps prevent the valve spindle from sticking in the closed position.

Conclusion: Is a Thermostatic Valve Worth It?

A thermostatic valve is a low-maintenance product that provides room-by-room temperature control, and its mechanical models need no batteries. Set correctly, it improves comfort and helps save energy by reducing unnecessary heating; how much is saved varies from home to home. For other plumbing products, see our mechanical plumbing and technical products categories.