The knob by the radiator has five numbers and a snowflake, yet no one ever included an instruction manual for it. That is where most household misunderstandings about heating come from: one person turns it to maximum to make the room warm up faster, while another turns everything down to zero before leaving for work, and the bill still comes in higher than it should. In this article, we explain what the numbers mean, which temperature works well in each room, and how much you can realistically save by turning it down by one degree.
What the numbers on a thermostatic head mean
The most important thing to understand first: the number on the knob is not the heating power, but the temperature you want in the room. Inside, the head has a sensor that measures the air around it and automatically opens or restricts the flow of hot water to the radiator. You set a target, not the intensity.
The individual positions correspond roughly to the following temperatures:
| Position | Temperature | Where it works well |
|---|---|---|
| ❄ | approx. 6 to 8°C | protection against the system freezing only |
| 1 | approx. 12 to 14°C | entrance hall, garage, utility rooms |
| 2 | approx. 15 to 16°C | bedroom |
| 3 | approx. 20 to 22°C | living room, lounge, study |
| 4 | approx. 22 to 24°C | bathroom |
| 5 | approx. 26 to 28°C | maximum setting, unnecessary in everyday use |
The ranges vary slightly depending on the manufacturer of the thermostatic head, so treat them as a reference rather than exact values. The principle is the same for all of them, however: the higher the number, the warmer the room should be before the radiator stops heating.
Why the setting does not affect how quickly the room heats up
This is probably the most common misunderstanding related to heating. When you return to a chilled apartment, your instinct tells you to turn the knob to maximum to speed up the heating process. But a thermostatic head does not work like a gas pedal.
If the room is cooler than the set temperature, the valve opens fully, regardless of whether it is set to three or five. Exactly the same amount of hot water flows to the radiator. The difference only appears at the end: at three, the radiator will cut off the supply when the room reaches 20 to 22 degrees, while at five it will continue heating until it reaches 26 or 28. The room will warm up just as quickly; the only difference is that in the second case, it will not stop when it has reached a comfortable temperature.
The result is that you pay for overheating, not for speed. If you want the room to warm up faster, uncovering the radiator and closing the door to the room is more effective than changing the settings.
What temperature should each room be
Setting the same temperature everywhere is convenient but costly. The biggest savings come from varying the settings: in the kitchen and bedroom, you simply do not need as many degrees as in the living room.
A useful starting point is the World Health Organization's guidelines (Housing and Health Guidelines). The WHO identifies 18°C as the minimum safe temperature for healthy adults during the heating season. Below this threshold, the risk of health problems increases, especially for children and older people, so this is not an area where you should force savings.
- Living room and lounge: 20 to 22°C. This is where you spend the most time sitting still, so you feel the cold most strongly.
- Bedroom: 15 to 18°C. Cooler air promotes better sleep, and it is warm under the covers anyway.
- Bathroom: 22 to 24°C. The only room where you are wet and undressed, so a higher temperature makes sense here.
- Kitchen: 18 to 20°C. The oven, cooktop, and refrigerator give off plenty of heat on their own.
- Rarely used rooms: minimum 15°C. No lower, because chilled walls begin to collect moisture.
Lower settings at night and when you are away
Turning off all the radiators before leaving for work seems like the simplest way to save money. In practice, it usually does not pay off, and it is worth knowing why.
Heat is not stored only in the air. Walls, floors, furniture, and the entire structure of the building store it. A few hours without heating cools not only the air, which warms up quickly, but also all those structures, which warm up slowly and at considerable cost. When you return, the heating system has to make up for the entire loss, using more energy than it would have cost to maintain a slightly lower temperature during that time.
That is why it is more sensible to lower it by 2 to 3 degrees, for example by turning the dial from three to two, than to turn it all the way down to zero. The house will not have time to get cold, and you will not pay extra to heat the walls back up.
How much you can save by lowering the heating by one degree
There is a simple rule of thumb in the energy industry: each degree lower means around 5 to 8 percent less thermal energy used, or about 6 percent on average. The same figure is cited independently by the German Energy Agency, dena, and the Polish heating-industry campaign “20 degrees for the climate,” run by the Izba Gospodarcza Ciepłownictwo Polskie.
Where does that figure come from? A radiator gives off heat to compensate for the difference between the temperature in the room and the temperature outside. During the heating season, this difference averages around a dozen degrees. One degree is therefore roughly one twelfth of all the work the installation has to do, which is where those few percent come from.
An important caveat: this is a rule of thumb, not a fixed physical constant that is the same for every home. In a poorly insulated building, the effect measured in kilowatt-hours will be noticeably greater because the losses are higher. In a well-insulated house, where the sun and the occupants' daily activities provide a significant amount of heat, that same one degree will make a proportionally smaller difference.
Why the dial in an apartment block does not go below two
If you live in a multifamily building and the thermostatic head has a limiter that prevents you from turning it down further, this is neither a malfunction nor an act of malice by the building administration. It results from a requirement set out in the Regulation of the Minister of Infrastructure on the technical conditions to be met by buildings and their location.
It is worth clarifying right away who this provision is addressed to, because it can be a source of misunderstandings. Paragraph 134 specifies the properties that an installation must have: in buildings supplied by a district heating network or by their own oil-, gas-, or electricity-powered source, the regulators must operate automatically and allow the temperature to be lowered, but not below 16°C in rooms with a design temperature of 20 degrees or higher. This is a technical requirement concerning the equipment and installation design, not a ban directed at the tenant or a provision stating how many degrees you are allowed to have in your living room.
Where did this particular limit come from in the first place? Mainly from concern for the building itself. Walls that have cooled down significantly, especially in corners, around windows, and behind furniture, begin to collect condensation, and from there it is only a short step to damp and mold. In a living room that rarely drops below this value, the issue is mostly theoretical, but in a less frequently used north-facing room, it is very practical. The second, secondary reason is that a cooled-down apartment draws some heat from neighboring apartments through the walls.
There is also a purely financial issue worth knowing about when planning savings in an apartment building. With billing based on heat cost allocators, regulations usually provide for a minimum variable charge and adjustment factors for apartments in less favourable locations. In practice, this means that lowering the temperature very significantly does not always reduce the bill in the same proportion one might expect from the allocator readings. You can find the rules in the billing regulations of your housing cooperative or condominium association.
Finally, an important qualification: the same rule does not apply to detached houses, farm buildings, individual recreational buildings, or apartments equipped with their own heating system. If you live in a house or have your own boiler in your apartment, you can set the heads as you see fit, including to the snowflake setting.
Most common mistakes
- The radiator is blocked by furniture or covered by a curtain. The problem is twofold. Heat spreads less effectively throughout the room, and the sensor in the head measures the air trapped behind the obstruction, which is warmer than the rest of the room. The head therefore assumes that the room is already warm and closes the valve, even though the room is still cold.
- Dusty fins. A layer of dust between the fins acts like a blanket and significantly limits heat transfer. Vacuuming the radiator before the heating season takes just a few minutes and can make a difference to heating costs.
- The head is pointing in the wrong direction. The sensor should be exposed to the air in the room. If the head is turned toward the wall or points downward, toward the pipes and the radiator itself, it measures their heat instead of the room temperature and switches the heating off too early. A correctly installed head is positioned horizontally and “looks” into the room.
- Ventilating with the radiator turned on. The inflow of cold air causes the thermostatic head to open the valve fully, making the radiator work at full capacity to heat air that will soon escape through the window. The correct order is: turn the head to the lowest setting, ventilate intensively for 5 to 10 minutes, close the window, and turn the head back up.
What to do if adjustment alone is not enough
Adjusting the thermostatic heads is the first and simplest step, but not the only option available to you. Sometimes, despite the correct settings, some rooms heat up much less than others. In that case, the problem is no longer the heads themselves, but how water is distributed between the individual radiators throughout the system - a phenomenon known as hydraulic balancing.
A separate, independent control is the temperature of the water leaving the boiler, set on the boiler itself or its controller, as well as the circulation pump setting, which determines how much of this water circulates through the system. These are three different levels of control, and only together do they provide a complete picture of heating costs.
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Frequently asked questions
What do the numbers on a thermostatic radiator valve mean?
The numbers correspond to the target room temperature, not the heating intensity. Approximately: 1 is around 12 to 14°C, 2 is 15 to 16°C, 3 is 20 to 22°C, 4 is 22 to 24°C, and 5 is 26 to 28°C. Exact values vary slightly between valve manufacturers.
Does setting the valve to maximum make the room heat up faster?
No. The radiator valve opens fully regardless of the selected number when the room is cooler than the set temperature. A higher number only means a higher threshold at which the valve closes, resulting in higher energy consumption rather than faster achievement of a comfortable temperature.
How much do I save by lowering the heating by 1 degree?
Around 5 to 8%, with an average of 6% of heating energy consumption for each degree lowered. The same figure is given by the German Energy Agency, dena, and the Polish heating industry campaign "20 Degrees for the Climate." The effect will be greater in a poorly insulated home and smaller in a well-insulated one.
Why doesn't the valve in my apartment allow me to lower the temperature below setting 2?
This follows from Paragraph 134 of the Regulation of the Minister of Infrastructure on the technical conditions to be met by buildings. The provision specifies that in multi-family buildings supplied by a district heating network or their own oil-, gas-, or electricity-powered source, regulators must allow the temperature to be lowered, but not below 16°C. This is a technical requirement for the installation, not a ban directed at residents. It does not apply to single-family homes or apartments with their own heating system.
Why does a radiator covered by furniture heat less effectively?
The sensor in the thermostatic radiator valve detects the temperature of the air trapped directly next to the radiator. If this air is warmer than the rest of the room because the radiator is covered by furniture or a curtain, the valve closes prematurely, before the entire room has had time to warm up.
Is it worth turning off the heating completely when no one is home?
Usually not. Walls and floors store heat, so cooling them down completely later requires more energy to heat them back up than maintaining a steady, slightly lower temperature for the same amount of time. It is safer to lower the temperature by 2 to 3°C instead of turning the radiator off completely.
