With the arrival of the first cold weather, it is also time to turn on the radiators. There are those who keep them to a minimum for fear of the bill and those who, as soon as they feel cold, turn the knob to number 5, convinced that this way the room will heat up faster.
Yet, that very small knob installed next to the radiator can help us reduce energy waste and save on heating, as long as we know how to use it.
We are talking about the thermostatic valve, present on many radiators and recognizable by the numbers that generally range from 1 to 5. Numbers that we often adjust without thinking too much and which, contrary to what one might imagine, do not indicate the power of the radiator.
But then what do they mean? And above all, what number should be set to heat the house without consuming unnecessarily?
What do the numbers 1 to 5 on the radiator valve mean?
The first thing to know is that the numbers on the thermostatic valve correspond to indicative room temperatures, not the rate at which the radiator produces heat.
The valve automatically regulates the amount of hot water passing through the radiator based on the temperature detected in the room. When the environment reaches the set one, the device gradually reduces the flow of hot water.
On many models the scale works approximately like this:
These values are used, for example, on some Caleffi and Danfoss thermostatic valves, but are not identical for all models. Some manufacturers have slightly different temperatures, so it’s always worth checking your valve’s instructions.
The number 3, generally associated with a temperature of around 20°C, is often a suitable setting for the environments in which we spend a good part of the day.
However, if we want to keep a bedroom a little cooler, we can try a lower position and check the actual temperature with a thermometer.
Does putting the valve on number 5 make the room heat up faster?
This is probably the most common mistake. When we enter a cold room, it is natural to turn the knob to 5, thinking of giving a sort of acceleration to the heating.
In reality, setting the valve to the maximum number does not make the room heat up faster.
If the room temperature is already much lower than desired, the valve is normally open to allow the hot water to pass through. Setting it to 5 does not make the water hotter and does not automatically increase the power of the system. What changes is the temperature we want to reach.
Let’s take an example: if it is 16°C in the living room and we want to reach 20°C, setting the valve on 3 is generally sufficient. Turning it to 5 means asking the device to continue to pass hot water even above 20°C, until the room reaches the temperature corresponding to the new setting, if the system is able to get there.
The risk is finding yourself with a room that is too hot and consuming more energy than necessary.
What number to set to save on heating?
Not all rooms need the same temperature. And this is precisely where thermostatic valves become useful. In the living room, where we spend several hours, a temperature around 19-20°C may be sufficient. In the bedroom, however, many people prefer to sleep in a slightly cooler environment.
For a room that is used little during the day, it may make sense to maintain a lower temperature, but avoid letting it cool excessively, especially if there are humidity or condensation problems.
The advantage of valves is precisely this: they allow each radiator to be adjusted according to the needs of the individual room, without necessarily having to keep all the rooms at the same temperature.
According to ENEA, lowering the internal temperature by one degree can save up to 10% on fuel consumption for heating.
Naturally, the actual savings depend on various factors, including the insulation of the house, the external temperature, the type of system and usage habits. You don’t just need to turn a knob to automatically get a certain reduction in your bill.
What is the snowflake symbol on the valve for?
In addition to the numbers, a small snowflake or asterisk appears on many thermostatic valves. It is not a decorative symbol: it indicates the antifreeze function.
When the knob is positioned on this symbol, the valve lets hot water enter the radiator if the temperature detected drops below a certain threshold, which can be around 5-8°C depending on the model.
It serves above all to limit the risk of the water in the system freezing during periods of intense cold. Be careful, however: the valve’s antifreeze function alone does not guarantee the protection of the entire system. To work, there must be hot water available and the heating system must be able to activate.
It is therefore not a solution for normally heating a room nor an absolute protection when leaving an empty house for many days.
The mistake of the curtains in front of the radiator
There is another detail that can compromise the functioning of thermostatic valves and which often goes unnoticed.
The valve head contains an element that is sensitive to the temperature of the surrounding air. If it is covered by a heavy curtain, hidden behind furniture or closed inside a radiator cover, it may detect a different temperature than the actual temperature in the room.
The result? The valve could reduce the flow of hot water too soon, leaving the rest of the room still cold. For this reason it is important to leave the area around the head free and not to cover the radiators with furniture or curtains that prevent the heat from spreading correctly.
ENEA also recommends avoiding obstacles in front of radiators, precisely to reduce energy waste.
Is it worth constantly changing the number on the valve?
If we have reached a comfortable temperature in the house, there is no need to continue turning the knob.
The thermostatic valve is designed to automatically regulate the flow of hot water. Once we have chosen the desired temperature, we can let it work.
Of course, we can change the setting when needs change: for example, if a room remains unused for many hours or if we prefer a different temperature during the night.
It should also be remembered that the valves work together with the rest of the system. If the central thermostat has already turned off the boiler, opening a radiator valve all the way will not automatically restart the heating. Before turning on the radiators, therefore, it is worth taking a few minutes to check the knobs and understand what temperatures we are actually setting.
