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What is a condensing boiler?

In this guide, we discuss what a condensing boiler is and how it helps you get the most out of your heating

What is a condensing boiler?

We’ve all heard of condensing boilers, but do we actually know what they are?

Since 1st April 2007, it has been a legal requirement that all new gas boilers, including new gas combi boilers, installed in England and Wales must be condensing boilers.

These are units that use condensing technology to maximise the heat they generate from the fuel they burn.

Before this technology was introduced, most gas boilers wasted 30-50% of the heat they produced due to combustion gasses escaping into the flue.

How does a condensing boiler work?

A condensing boiler works by capturing the heat in the flue gasses and recycling it back into heating system. This is then used to preheat the cold water entering the unit before being sent back out into the system. To keep this process safe, the temperature of the flue gas is reduced from 130℃ to 50℃.

This rapid fall in temperature causes a huge amount of condensation, which is where the boiler gets its name from. In fact, the amount of condensation can measure as much as 2 litres every hour and is simply drained away into your wastewater through the condensate pipe.

This clever solution allows the boiler to reuse energy that is already there, allowing it to save you money on your heating bills and reduce the amount of CO2 that you and your household emits.

What size condensing boiler do I need?

To work out what size condensing gas combi boiler to go for, you’ll need to assess how much water you expect to consume based on the number of people in your house and how many rooms to you need to heat.

For most people in a 2-3 bedroom property, with one bath and one shower, a condensing combi of between 24 -30kW will be more than adequate.

For those in larger homes, with 4 bedrooms or more or one with en-suite bathrooms, it would be advisable to go for a 30-35 kW boiler.

Can anything go wrong with a condensing boiler?

Due to advancing technology, modern condensing boilers are extremely reliable. However, like most appliances, things can sometimes go wrong.

Among the most common boiler faults is a frozen condensate pipe, which can occur during extremely cold weather, and is also more likely to happen if it’s been fitted to the outside of your property.

This can be be a reason why people with condensing boilers suddenly stop getting hot water during the winter months. However, thawing a frozen condensate pipe can often be quick and easy.

If you’re unable to work out the problem and fix it yourself, it may be time to call a qualified engineer to carry out a boiler repair.

Are there alternatives to condensing boilers?

While the vast majority of modern-day boilers are condensing combis, there are some alternatives on the market that you may want to consider.

Biomass Boilers

Biomass boilers work in very much the same way as conventional heating systems. But instead of burning traditional fuels like gas and oil, they produce heat by burning more sustainable fuel sources in the shape of wood pellets and wood chips.

They appeal to environmentalists more than any other form of heating as the carbon dioxide released during combustion was originally absorbed while the tree was growing.

Air Source Heat Pumps

Air source heat pumps absorb heat from the air outside and use it to heat the inside of your home, as well as provide you with low-cost hot water.

These pumps are usually the air-to-water kind and require electricity to run. However, the heat they can extract from outside is often greater than the energy input required.

Ground Source Heat Pumps

Ground source heat pumps also known as geothermal heat pumps, use a network of pipes that are buried in your garden to extract heat from the ground.

This heat is increased further by the pump at ground level and is used to heat everything from radiators in your home to underfloor heating and even hot water.

Electric Storage Heating

The least common alternative is electric storage heating. This uses cheap off-peak electricity to store heat in large, insulated containers of water or bricks. This heat is released by water which is pumped by the central heating system through the store and into the radiators.