Dossier ENGIE
Setting Your Gas Boiler's Hot Water Temperature Correctly: Our Expert Advice
Adjusting the heating temperature of your gas boiler is essential both for maintaining thermal comfort and for reducing energy consumption, whether your boiler is used solely for heating or also for domestic hot water production. ENGIE shares its recommendations for choosing the ideal temperature for the hot water produced by your gas boiler.
A gas boiler can perform several functions. It can provide heat for your radiators or underfloor heating through a central heating system, while also producing domestic hot water. Whatever its purpose, the operating principle remains largely the same: the boiler burns gas to heat a heat-transfer fluid (most commonly water), which circulates through a network of pipes to supply heat emitters and/or heat water stored in a hot water cylinder.
This is why adjusting the temperature at which your boiler heats this fluid is so important. If the temperature is too low, your comfort may suffer. If it is too high, your energy bills can increase significantly. To help you make the right adjustments and find the ideal heating temperature, ENGIE has created this guide.
Prolongez la durée de vie de votre chaudière
Jusqu'à 12%(1)
How to adjust your heating water temperature
Before going any further, it is useful to clarify what is meant by heating water. This is the water that circulates within the closed hydraulic circuit of your central heating system. In other words, it is the water heated by your boiler and then distributed through your pipework to your heat emitters, such as radiators or underfloor heating.
But what temperature should this water be heated to in order to provide optimal comfort while making efficient use of energy?
Recommended heating water outlet temperatures according to your heat emitters
The ideal boiler temperature setting depends on the type of heat emitters installed in your home. During winter, the recommended outlet temperatures are generally as follows:
High-temperature radiators (smaller radiators): 70°C
Medium-temperature radiators: 60°C
Low-temperature radiators (for example cast iron radiators or aluminium radiators): 45°C
Underfloor heating systems: 35°C
During spring and autumn, when outdoor temperatures are milder, these settings can often be reduced slightly. However, whenever possible, prioritise adjusting the thermostatic radiator valves or your room thermostat before changing the boiler temperature itself.
The process is relatively straightforward. Adjust the heating temperature gradually. If you wish to lower the temperature, do so in stages until you find the right balance. As soon as your thermal comfort is no longer satisfactory, increase the setting progressively until you reach an appropriate level.
Automatic temperature control
You can also choose automatic boiler regulation based on weather conditions by installing an outdoor temperature sensor. This solution automatically accounts for cold spells and milder weather conditions, adjusting heating output accordingly.
Should you adjust your heating water temperature based on the temperature you want in each room?
If you want to optimize the temperature of the water circulating through your heating system, it is recommended that you install two types of equipment: thermostatic radiator valves and/or a room thermostat, ideally with multi-zone functionality.
These systems allow different rooms to be heated to different temperatures according to their specific needs, helping to reduce unnecessary heating demand.
To further limit unnecessary heating, you may also install a heating programmer.
This allows temperatures to be adjusted according to:
Occupancy patterns: temperatures can gradually increase before you return home in the evening and decrease by two or three degrees during periods of absence, typically reaching around 16°C.
Time of day: temperature reductions can be automatically scheduled during the night.
The main benefit of these systems is that they prevent sudden temperature increases, which can lead to significant energy consumption. In most cases, it is more efficient to heat a home gently over a longer period than to heat it intensely for a short time.
For even greater control, you can opt for remote heating management using a smart thermostat. With this solution, you can adjust temperatures remotely via a smartphone, tablet, or computer. Built-in artificial intelligence also enables more precise and flexible temperature management.
Habits and practical tips to reduce your boiler's heating temperature
If you want to lower the heating water temperature in your system while maintaining comfort, it is equally important to reduce your overall heating requirements.
One of the most effective approaches is to minimise heat loss. Consider:
Improving your home's insulation;
Upgrading window insulation without replacing the windows, or replacing them and benefiting from available financial support;
Installing curtains to reduce the sensation of draughts;
losing shutters at night;
Separating heated rooms from unheated areas;
Installing draught excluders under doors.
You can also increase perceived warmth by adding rugs to floors or wearing warmer clothing indoors.
ADEME's recommended temperatures for each room
According to ADEME (France's Agency for Ecological Transition), recommended temperatures vary depending on the room:
Bedroom: 17°C to 18°C;
Kitchen: maximum 19°C, as cooking appliances and occupant activity already generate heat;
Living areas: between 19°C and 20°C;
Bathroom: 19°C to 20°C, or 22°C while in use, and 17°C the rest of the time.
These recommendations are important because ADEME estimates that reducing room temperatures by just 1°C can lower gas consumption by approximately 7%(1).
What is the ideal temperature for domestic hot water?
Does your boiler also produce domestic hot water (known in France as Eau Chaude Sanitaire, or ECS)?
For optimal comfort, domestic hot water should generally be heated to between 45°C and 55°C.
You will quickly notice if the water temperature is too low. Even with the tap fully set to hot water, the water may feel lukewarm. In addition, your hot water cylinder may appear to run out more quickly.
Conversely, if the domestic hot water temperature is set too high, the water may become uncomfortably hot, making it necessary to mix in a significant amount of cold water before use.
Why is it important to adjust your boiler correctly?
If the temperature of either your heating circuit water or your domestic hot water is too low, your comfort levels will inevitably be affected.
However, setting your boiler temperature excessively high is not recommended either. It forces the gas boiler to operate continuously at maximum or near-maximum capacity, increasing wear and tear on the system over time.
In addition, limescale begins to form more rapidly when water temperatures exceed 60°C. Scale build-up can damage both pipework and heating equipment.
Excessively high settings also lead to unnecessary gas consumption, resulting in avoidable energy costs.
For all these reasons, regular maintenance by a qualified heating professional is strongly recommended. Ideally, choose an installer who holds both RGE (Reconnu Garant de l’Environnement Government-recognised environmental certification) and Qualigaz certification.
During annual servicing visits, the technician can optimize both the heating circuit temperature and the domestic hot water temperature, helping you combine comfort with energy savings.
Boiler water temperature settings: key points to remember
The correct temperature settings depend on whether your boiler is used exclusively for heating or also produces domestic hot water.
To ensure comfort while helping to control energy costs, heating water temperatures should be adapted to the type of heat emitters installed in your home, ranging from approximately 70°C for high-temperature radiators to 35°C for underfloor heating systems.
Domestic hot water should generally be heated between 50°C and 60°C to ensure both comfort and health protection.
Several solutions are available to regulate heating water temperatures effectively, including thermostatic radiator valves, room thermostats (preferably multi-zone models), and smart thermostats.
It is also important to maintain room temperatures in line with ADEME recommendations, particularly around 19°C in living areas.
Finally, remember that your heating professional is there to advise you. During your annual boiler service, do not hesitate to ask for personalized recommendations.
What maintenance does my central heating system require?
In addition to the legally required annual boiler service carried out by a certified professional in France, there are several simple maintenance tasks you can perform yourself. These include checking your boiler pressure, cleaning radiators, and bleeding radiators when necessary.
What financial assistance is available when replacing a boiler?
If you use an RGE-certified installer, you may qualify for several forms of financial assistance available in France without income conditions. These include the Energy Savings Certificates scheme (CEE), incentives such as the ENGIE Energy Savings Bonus (Prime Économie d’Énergie ENGIE), the Eco-interest-free loan (Éco-prêt à taux zéro), and the reduced 5.5% VAT rate for eligible energy renovation works.
Other schemes, including MaPrimeRénov', MaPrimeRénov' Sérénité, the Coup de Pouce Chauffage grants, and the Energy Voucher (Chèque énergie), are subject to income thresholds and may not be available above certain household income levels.
