Condensing vs Non-Condensing Boiler: what’s the difference?

Condensing vs non-condensing boiler – what’s the difference? Quite simply, condensing boilers are 10-25% more energy efficient. Not only can they save you several hundred pounds on your annual energy bill, they’re also better for the environment. But how do they do this? When you’re looking to buy a new condensing boiler or simply want to learn how they work, this article will point you in the right direction.

Condensing vs Non-condensing boiler: what’s the difference?

When a boiler burns fuel, one of the byproducts of the combustion process is water vapour. This water vapour – steam – contains heat. Imagine that you open a window, put a pan of water on the hob, bring it to the boil, and leave it there until all the water boils away into steam. The heat you’ve paid for has literally gone out of the window.

This principle is effectively what happens in a non-condensing boiler. The water vapour produced from the combustion process is simply expelled via the flue, heating the outdoors instead of your home or your hot water.

Condensing vs Non-condensing boiler: what they do differently

Condensing boilers don’t let that heat go to waste. Instead, they draw so much heat out from that vapour, it condenses back into water. This recovered heat is then used to heat the water for your radiators or the hot water tank. This means that condensing boilers require less fuel to generate the same amount of heat – and fewer carbon emissions. They’re better for the environment as well as for your wallet.

The condensed water – or condensate as it is known – is collected in a trap before being discharged into the sewer via the condensate pipe. These components are usually plastic, as the slightly acidic condensate would react with metal pipework. Most boilers eject condensate in small spurts so that a constant dripping doesn’t freeze and block the pipe. Frozen condensate pipes are an extremely common reason for a winter boiler breakdown.

Condensing vs Non-condensing boiler: how efficient are they?

Very efficient – you can usually expect an energy efficiency of at least 90% from a condensing boiler. This means that for every £1 you spend on your energy bill, 90p is directly going towards heating your home and the hot water. Compare this to a non-condensing boiler, which may only have an energy efficiency of 70-80%. In older boilers, that figure may even be as low as 50-60%, which amounts to a tremendous waste of money and energy. Condensing boilers are always more energy efficient than non-condensing boilers.

UK energy efficiency regulations require that all gas boilers installed after 1st April 2005 and all oil-fuelled boilers installed after 1st April 2007 must be condensing boilers.

Condensing vs Non-condensing boiler: how much money will I save?

Of course, the answer to this question depends on the efficiency of the boiler you wish to replace. According to The Energy Saving Trust in, replacing a Band G non-condensing boiler with a Band A condensing boiler and modern central heating controls, you can save up to £340 a year on your energy bills. You’ll also dump 1,500 kg less carbon dioxide into the environment, helping to shrink your carbon footprint.

Is it still possible to install a non-condensing boiler?

Yes, but only in circumstances where a qualified heating engineer has determined that a condensing boiler is unsuitable for the property. A points system is used to determine this, and if a score of over 1000 is reached, the engineer will issue a certificate to say that a non-condensing boiler can legally be fitted. It is extremely important that the homeowner does not lose this certificate should they wish to sell the property in future, as it confirms that the existing installation of a non-condensing boiler is legal.

What other types of boiler are there?

The issue of condensing vs non-condensing boiler relates to energy efficiency rather than the actual type of boiler for a particular central heating system configuration.