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The condensing boiler is 15 to 20% more efficient than standard equipment. It offers better performance and the advantage of recovering the heat of the water vapor from combustion.

Choose a condensing boiler

If you want to change your boiler for a more efficient model, should we change energy?

A condensing boiler can substitute for almost any model in use, regardless of the energy used. It can be connected to all types of hot water heating systems, by checking the ventilation of the housing and the existing flue.
On the other hand, if the condensing boilers are just as efficient as each other, there is still a difference depending on the energy: the gas produces more water when it burns than fuel, which increases the amount of energy to be recovered in the water vapor. That said, the choice of energy depends on many other parameters, both technical and economic, even aesthetic. This choice must be made after having been studied on a case by case basis with a qualified installer.

Can a condensing boiler be integrated into an existing installation?

A condensing boiler can be connected to any hot water heating system. However, it is preferable, for maximum efficiency, to associate it with low-temperature transmitters: underfloor heating (return water at less than 40° C) and / or heat-treated radiators (return water at less than 50° C).° C).
In fact, the lower the temperature of the return water of the heating loop, the more the boiler condenses and optimizes its performance. In addition, the replacement of an old appliance by a condensing boiler must be done taking into account the particularities of this technology. This involves studying the possibility of evacuation of the combustion products from the boiler on the existing installation (reuse of an old duct, renovation of said duct, casing, installation of a sealed combustion circuit appliance, etc.).
Condensate drain must also be evaluated before starting work. It is also important to ensure that the characteristics of the premises allow its implementation. Solutions exist for all cases, and the installation of a condensing boiler does not usually pose any particular difficulty: the professional who intervenes evaluates all these parameters before presenting his quote.

Does condensation require modifying evacuation systems?

The condensates resulting from the combustion are acidic, and certain conduits can not support them... An old conduit can however be reused to make pass a tube of resistant material: this operation is called the "Casing". There are also processes that allow reuse of an old flue to pass through the exhaust system of a sealed circuit appliance. As can be seen, it is necessary to treat the evacuation of combustion products during the installation of a condensing boiler on an existing installation, but the answer is not necessarily to destroy the old duct to mount it. a new one: here again, each installation is a special case.

Should we choose a boiler of equivalent power?

When changing the boiler, always reevaluate the power required. Indeed, in individual houses, it is very rare that there has been no improvement work, such as changing windows, insulating attics, etc., especially in buildings that sometimes have more than fifty years. It is also important to assess the current and future needs of the future boiler, which must always be powerful enough to ensure both heating alone and heating + hot water production.
If insulation work is planned later, the capacity of the devices to adapt the power to the needs poses no problem: on the contrary...
Condensing boilers perform better in mid-season because their ability to recover energy from the water is better. Here too, the expertise and advice of a professional will be welcome.

Is it easy to combine this type of boiler with renewable energy?

From the moment the installation uses hot water heating, the consumer has all the elements to easily integrate appliances using a renewable energy source, whether for heating or hot water production. For example, given the current offer, if we take advantage of the replacement of an old boiler by a condensing boiler to combine solar thermal (an individual solar water heater), the extra cost is sometimes low. Most manufacturers offer compact solutions that combine a solar water heater and a condensing boiler into one piece of equipment, further limiting the footprint in the home.
This is also the case of hybrid generators that group together in a single set a boiler, an air-water heat pump, and a regulation that drives the whole in a concern for energy optimization.

Optimize by regulating

The implementation of a outdoor temperature sensor associated with a room sensor (not to be confused with the all-or-nothing room thermostat, certainly less expensive, but which is a heresy with a condensing boiler), allows to automatically adjust the starting temperature of the water to the needs and to obtain permanently the lowest return water temperature possible. The installation of an external sensor on a heating circuit set at 80/60° C allows the boiler to condense more than 90% of the time.
In addition, a regulation on the outside temperature makes it possible to continuously diffuse water at the right temperature in the radiators and to obtain a better thermal comfort.

Stop the flow noises!

If you notice water flow sounds accompanied by abnormal cooling of the upper part of your radiators, it means that water is poorly distributed in the pipes as well as in the devices and it is time to purge these.

  • To do this, we must start with stop the circulation pump of the boiler. On old models, simply press the on / off button of the pump and, on recent models, to put in position "summer".
  • It is then necessary to slightly unscrew the plugs of the traps (usually located on the top of the radiators), taking care to screw them again as soon as the water escapes.
  • It is also advisable to purge the pipes, this time unscrewing the traps placed on the high pipes of the installation (on the ceiling).
  • Finally, Verify the pressure and, if necessary, add water in the circuit until a pressure ideally located between 1 and 2 bars.

When is it necessary to change the boiler?

If the boiler is old and its technology is "standard" class, it may be wise to change and opt for a more efficient equipment and more economical.
However, the replacement of a wall-mounted low-temperature or condensing boiler of more than ten years is not necessarily necessary, provided that it is well maintained.
Annual boiler maintenance is in this case mandatory since the decree of September 15, 2009, which defines that a visit must be carried out each year by a professional for all the boilers in individual house. Once the interview is done, the professional has the obligation to deliver a attestation within 15 days following his visit, that the occupant must keep for a minimum period of two years.
Attention: the certificate of maintenance of the boiler may be required by companies and mutual insurance to ensure the home in case of disaster.

Install a condensing boiler

Diagram of the operation of a condensing boiler

If you already have an individual chimney flue, which only evacuates the products of combustion, the installation of a condensing boiler does not require a review of the exhaust system.
However, it will be necessary to consider "tubing" this conduit (that is to say, the double), to protect it from moisture caused by condensation and acidity of the condensates evacuated.

Solar gas and balloon

Condensing boiler

It integrates a solar flask of 150 l. Modulating, this gas condensing boiler is offered in two models with a power of 3 to 29.5 kW and 3.6 to 33 kW. Control panel control on the front panel.

"Pharos Opti" of Chaffoteaux. € 3,399 excluding taxes *.
Strong point: operation for heating and DHW production by micro-accumulation in addition to the solar system.

A hybrid condensing boiler

Viessmann condensing boiler

A 19 kW condensing gas boiler, a 130 liter hot water tank, an aerothermal heat pump (COP up to 5.08) and a hydraulic module are combined into a hybrid handset.
Vitocaldens 222-F from Viessmann. Starting from € 11,133 excl.

Strong point: 80% of the heating needs are covered by the CAP, greatly limiting the operating costs of the installation.

A condensing boiler in renovation

Condensing boiler

In heating alone or with DHW production, this gas condensing wall-mounted boiler is very compact. It easily replaces any boiler thanks to its width of 445 mm. Note its high capacity of hot water production (flow 20 l / min).

Atlantic-Guillot "Naema", 12 or 20 kW. From € 1,945 excluding tax.
Strong point: connected, it is piloted remotely and can track its consumption.

A boiler with oil condensation

De Dietrich Thermal Condensing Boiler

With a capacity of 19 to 32 kW, this oil boiler for heating alone is available in low temperature or condensation. Control by programmable control panel on external probe.


"NeOvo Condens / EcoNox" by De Dietrich Thermal. Starting from € 4,076 excluding tax.
Strong point: a 110 or 160 liter balloon included in the overall dimensions of the installation also makes it possible to produce the ECS.

A modulating gas condensing boiler

Condensing boiler from Vaillant

Available in five power ratings from 14 kW to 65 kW, this gas-fired wall-mounted heating boiler alone provides optimized combustion and power modulation from 18 to 100%. Automatic regulation.

"EcoTEC plus systems" from Vaillant. Starting from € 2,850 excluding VAT.
Strong point: may be associated with a conventional sanitary preparer or a solar system (sensor and balloon).


Video Instruction: When to use a condensing boiler