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What Is A Condensing Boiler And How Can I Maximise Its Efficiency
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What Is A Condensing Boiler And How Can I Maximise Its Efficiency?

What is a condensing boiler?

A condensing boiler captures condensation when burning gas. The condensation can only occur under certain conditions, but when the conditions are correct, we are able to capture the condensation and use the heat stored within it to contribute to the heating of our central heating system or hot water.

The disillusion that most people get is that when they have a new condensing boiler installed they automatically save on their gas bills. This is not the case, because the installer is not educating their customer in how to fully maximise the amount of condensation produced and how to maximise the amount of condensation captured.

You will probably recognise what looks like smoke, bellowing out of your flue. The more you see, the less you are capturing. Some of the boilers I have set up burn gas and no water vapour is visible. We achieve maximum condensing and that is when we are making the best saving.

How can you tell if you have a condensing boiler?

How do you know if your boiler is a condensing boiler?

Apart from having the water vapour plume from the flue, the best way to know if your boiler has is a condensing boiler or not is by looking at the pipe-work to it.

The condensate which is produced by the boiler is acidic, which means that it has to be removed from the boiler using a plastic pipe. The way the plastic pipe can vary, different situations and boilers require different condensate pipe-work.

Most commonly the condensate pipe-work is connected to the boiler using a white plastic pipe which is about 23-25mm in diameter or 3/4″. These can be on either the right hand side or the left hand side of the boiler. It all depends but be on the look out for the plastic pipe.

How much energy can be gained when the boiler is condensing?

How much energy can be gained when the boiler is condensing?

Modern boilers capture a lot of heat from the gas that we burn, wether it’s in condensing mode or not. The average modern boiler can be around 90% efficient. This basically means that if you burn £1 of gas 90 pence of that pound would be transferred into the heating or hot water system. so 10% is released into the atmosphere as wasted heat. However, If you’re able to keep your boiler in condensing mode for as long as possible you can gain even more energy.

Out of that 10% of usually wasted heat, a boiler that is in condensing mode will capture a further 8% of the heat and transfer it into heating energy for our central heating system.

Efficient controls hold the key to a happy boiler

Modern central heating controls can create a happy environment for your boiler, thus helping it to increase its life span.

The way we control our heating systems has massively improved over the years. We are moving on from the on-off control strategy that we have used for the past 50 years and we’re now moving into an era where are utilising modulating controls, such as weather compensation and Opentherm.

The new controls reduce the boilers work load massively and ensure the boiler runs at a temperature which is equally matched the actual heat requirement of the building, This changes on a daily basis, sometimes hourly. The warmer the outside the temperature the lower your boilers working temperature needs to be. The lower the boilers temperature the better. This also reduces stop-starts meaning the boiler will live longer.

These control strategies have been explained in much more detail in our resource centre so if you’re interested in learning more be sure to visit that section, or follow the links above.

How does condensing mode occur?

Condensing mode occurs under certain conditions. In modern boilers the transfer of heat from the gas being burnt into the heat exchanger is so good that the flue gas temperature is reduced to a point where water vapour occurs. This vapour can stick to the surface of the heat exchanger if the temperature of the heat exchanger is 57°C or less.

So the best way to achieve this is to have your boiler thermostat set to a low enough temperature to give you the comfort that you need within your home but to also ensure that the central heating return temperature is 57°C or less. This is achievable most of the year, but during extra cold spells during the winter this might not be possible.

Using something called Weather Compensation or Open Therm will ensure that the boiler uses the least amount of heat to obtain the comfort temperature you desire all year round. This automatically adjusts the central heating temperature to ensure maximum condensing.

It is very important your central heating system is balanced correctly as well. Balancing your central heating system will slow the flow of water down to give the radiators a chance to disperse the heat, so that when the water returns to the boiler it will be at a low enough temperature for the water vapour to condense.

The more we capture condensation the less amount of gas we require to burn to heat our homes.

In conclusion

Condensing boilers are becoming more and more popular now that non condensing boilers are past their service life. Condensing technology helps reduce our impact on the environment and also saves us on our gas bills. When I carry out annual services on condensing boilers I find that so many boilers are set up incorrectly. The boiler thermostats are set to 70 degrees and the system is poorly balanced so no condensing can occur. The end user has paid for a lovely new condensing boiler installation and are not benefiting from the extra savings that are available. Make sure you check your boiler thermostat is set as low as possible. If in doubt aim for around 55°C, This will cover your requirements for most of the year. Failing that, consider having some type of modulating thermostat.

I hope you found this useful, please take a look at some of our other posts.

Jamie Cureton
Jamie Cureton
Jamie is an extremely passionate heating engineer. He particularly enjoys the technology aspect of the industry especially how new heating controls work to help people save money and keep warm.
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