Setting Your Thermostat Correctly: What the Numbers Really Mean
Almost everyone turns the radiator thermostat in winter, yet hardly anyone knows what the numbers 1 to 5 actually mean. If you know the thermostat numbers and their meaning, you heat more precisely, save real money and avoid the biggest misconception: that your home warms up faster with the dial turned all the way up. That is simply not true.
In this guide, we explain which temperature lies behind each setting, what the small symbols such as the asterisk, sun and moon mean and how to cut your heating costs noticeably with the right setting. This way, you get the most out of your heating system.
What the numbers 1 to 5 mean
The numbers on the thermostat do not stand for a heating power but for a target temperature in the room. Each setting corresponds to roughly four degrees Celsius. The range extends from around 12 degrees at setting 1 to about 28 degrees at setting 5. The following table shows how they correspond:
| Setting | Room temperature (approx.) |
|---|---|
| Asterisk (frost protection) | approx. 5 °C |
| Setting 1 | approx. 12 °C |
| Setting 2 | approx. 16 °C |
| Setting 3 | approx. 20 °C |
| Setting 4 | approx. 24 °C |
| Setting 5 | approx. 28 °C |
The thermostat regulates automatically: as soon as the set temperature is reached, it throttles the heat supply. Setting 3 is therefore the right choice for most living spaces, as it corresponds to a comfortable 20 degrees.
The biggest misconception: turning it all the way up heats faster
The most common mistake in heating: anyone who wants heat quickly turns the thermostat to setting 5. However, this achieves nothing. A thermostat regulates the target temperature, not the speed. At setting 5, the room does not warm up faster. The radiator simply heats for longer, far beyond the desired temperature, until it reaches the maximum of 28 degrees.
The result is an overheated home and unnecessarily high consumption. It makes more sense to choose the right setting straight away and give the heating time. The heat arrives just as quickly at setting 3 as at setting 5, only with the correct final value. If the radiator still stays cold at the top, bleeding often helps, as described in our guide Bleeding Your Radiators in 5 Minutes.
Lines and symbols: asterisk, sun and moon
Besides the numbers, many thermostats have additional markings. Between the digits there are usually three small lines, each representing the one-degree steps between the settings. This lets you adjust the temperature even more finely.
Below setting 1, there is often an asterisk or snowflake symbol. It stands for frost protection: in this position, the heating only kicks in when the temperature drops below about five degrees. This protects the pipes from freezing, for example in a rarely used room. Some thermostats also show a sun as the standard setting for around 20 degrees and a moon for the nighttime setback to about 14 degrees.
The right temperature for each room
Not every room needs the same temperature. Setting each room deliberately gives you comfort and savings at the same time. These guide values have proven effective:
| Room | Temperature | Setting |
|---|---|---|
| Living room | 20 to 22 °C | 3 to 4 |
| Bedroom | 16 to 18 °C | 2 to 3 |
| Bathroom | 22 to 24 °C | 3 to 4 |
| Kitchen | 18 to 20 °C | 2 to 3 |
| Hallway | 16 to 18 °C | 2 |
Rooms you rarely use do not need to be fully heated. However, never turn them off completely, because cold rooms attract moisture and promote mold. The frost protection position or setting 1 to 2 is a good compromise here.
How to save properly with the thermostat
The greatest savings potential lies in the room temperature itself. Just one degree less lowers heating costs by up to six percent. So if you go down from 22 to 21 degrees, you will hardly notice it, but you will save noticeably. Also make use of the nighttime setback: during sleeping hours, 16 to 18 degrees is perfectly sufficient.
Programmable thermostats that control the temperature automatically according to the time of day make things even more convenient. This way, the bathroom is warm in the morning and the home is cooler during the day while you are out, with no daily readjusting. You will find suitable thermostats and heating accessories in our Accessories and Spare Parts category. Our article 10 Tips for Greater Energy Savings provides more ideas for saving.
Classic, digital or smart: which thermostat is right for you?
The good old rotary thermostat with the numbers 1 to 5 does its job reliably, but it has one drawback: you have to make every change by hand. Anyone who has stood in a cold bathroom in the morning or come home to an overheated apartment in the evening knows the problem. This is where digital and smart thermostats come in.
A programmable thermostat automatically lowers the temperature at night or when you are away and heats up again in good time. Smart models can also be controlled via an app, and some even detect when a window is open so that they can briefly turn down the heat. Switching is usually straightforward, because the thermostat heads fit the common valves and can be swapped in a few minutes. Given savings of up to six percent per degree, this small investment often pays for itself within a single heating season. If you are already considering a modernization, this is an easy first step toward greater efficiency.
Frequently asked questions
Which thermostat setting corresponds to 20 degrees?
Setting 3 stands for around 20 degrees and is therefore the ideal basic setting for living spaces. To go one degree higher or lower, use the lines between the numbers.
Does it get warm faster at setting 5?
No. The radiator does not warm up faster. It just keeps heating for longer, up to 28 degrees. This overheats the room and wastes energy. Choose the desired setting right away.
What does the asterisk on the thermostat mean?
The asterisk stands for frost protection. In this position, the radiator only heats when the temperature drops below about five degrees, thus protecting the pipes from freezing.
Should I turn off unused rooms completely?
Better not. Rooms that have cooled down completely are prone to moisture and mold. Instead, choose setting 1 to 2 or the frost protection position.
Conclusion
The numbers on the thermostat are not heating power levels but fixed target temperatures: setting 3 means around 20 degrees and is ideal for most rooms. Knowing that turning the dial all the way up does not warm your home faster helps you heat more precisely and avoid unnecessary costs. With the right temperature for each room, the nighttime setback and a programmable thermostat, you can save significantly without sacrificing comfort. Even one degree less makes a difference of up to six percent. You will find suitable thermostats, heating accessories and spare parts in our shop under Heating.
