Traditional or condensing boiler: a guide to the differences

The boiler is one of the most classic and popular heating systems in Italian homes. For years, gas boilers have been the most common solution, but today they are gradually making way for more efficient, sustainable models, such as condensing boilers, and increasing use of smart, renewable technologies, such as heat pumps powered by photovoltaic panels. Confirming this change, the European Commission is launching the stop of gas boilers from 2040, marking a decisive shift towards environmentally friendly heating solutions.

Both traditional gas boilers and condensing boilers can boast distinctive long life and optimal performance over time, provided that regular maintenance - which is also required by law - is carried out, preferably on an annual basis. However, when we talk about the operating mechanics, energy efficiency and sustainability, there are some differences to consider. Let’s take a more detailed look at the two models.

How does a traditional boiler work?

A conventional gas boiler extracts heat from gas produced by combustion and transfers it to the water in the heating circuit. The process has four main stages:

• Combustion: the chemical reaction takes place inside a burner and involves gas (methane or LPG) and oxygen, generating a flame in the combustion chamber. 
  In open chamber boilers, oxygen for combustion is taken from the external environment where the boiler is located: in this case, the room where the boiler is installed must be properly ventilated and free from obstruction. However, this type of installation, now no longer required by law except in specific cases, must always be carried out outside the home.
  In the case of boilers with sealed chamber on the other hand, the combustion chamber is sealed off from the surroundings and requires a dedicated duct to supply oxygen from outside. These types of boilers can therefore also be placed in small, enclosed places, such as the bathroom. 
• Heat exchange: the gases produced by combustion heat the metal plates (usually copper or steel) of a heat exchanger, which in turn heats the cold water entering from the heating circuit. 
• Water distribution: once the set temperature has been reached, the hot water is then ready to be fed back into the heating circuit to distribute domestic heat and/or produce domestic hot water.
• Flue gas evacuation: residual flue gases in the combustion chamber are released outside via a flue pipe.   

So how does a condensing boiler work?

The operation of a condensing boiler involves an additional step that involves the recovery of waste heat from the flue gases, thus maximising thermal efficiency. Let’s look at how the process evolves: 

• Combustion and heat exchange: as with conventional gas boilers, the chemical reaction between gas (methane or LPG) and oxygen takes place in a combustion chamber and generates heat and fumes at a high temperature. These heat the first heat exchanger, which gives up some of the heat to the water in the heating circuit.
• Condensation: residual exhaust gases in the combustion chamber are not expelled, but recovered through a second heat exchanger. The water vapour contained in these gases is cooled and condensed here, producing additional heat that can be used to heat the water in the heating circuit. 
• Water distribution: hot water is fed back into the system for domestic heating and/or hot water production. 
• Flue gas evacuation: flue gases are evacuated only after they have released all their latent heat and this takes place at much lower temperatures than in conventional boilers.

The main differences between the two types of boilers

Traditional gas boiler

• Operating principle: the conventional boiler uses a single exchanger to transfer the heat of the combustion fumes to the water in the system, without any further heat recovery.
• Heat loss: the exhaust gases from combustion, still at high temperature, are expelled to the outside without using their latent heat. 
• Energy efficiency and consumption: energy lost in the flue gases results in lower efficiency and higher gas consumption to produce the same amount of heat.

Condensing Boiler

• Operating principle: in addition to the primary exchanger, it integrates a dedicated condensation section (secondary exchanger) that further cools the flue gases until the water vapour condenses.
• Recovery of latent heat: steam condensation releases additional energy (latent heat), which is transferred to the water in the system, allowing for a much higher efficiency.
• Energy efficiency and environmental impact: thanks to latent heat recovery, the condensing boiler offers better performance than a conventional boiler, resulting in lower gas consumption and fewer polluting emissions.
• Condensate management: the condensation phase produces a discharge liquid (condensate) that must be properly disposed of via a drainage pipe, a condition not found in conventional systems.

Conventional or condensing boiler, which is best?

The choice between a traditional gas boiler and a condensing boiler depends mainly on energy efficiency needs, running costs and compatibility with the type of system. A condensing boiler offers higher heat efficiency, so that gas consumption and pollutant emissions are reduced thanks to the recovery of latent heat from flue gases. 

Although condensing boilers have a slightly higher purchase cost, the initial investment is compensated for by the savings in the long run, especially in low-temperature systems (radiant panels) or in systems designed to take full advantage of condensation.

The best choice for your home

Domestic heating systems are evolving towards new technologies that value high energy efficiency and environmental sustainability. 

Enel Energia looks to the future with next-generation condensing boilers and innovative products and services for your home to rethink traditional heating systems with a view to optimising consumption and saving energy. 

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