Condensing Boilers - some comments


All boilers installed in the UK under normal circumstances should be condensing boilers, according to Government rules. This is part of their energy-efficiency drive, and the rules have been in force since 2005.

This hasn't happened in the USA, where customers can still install an old-fashioned non-condensing boiler if they wish.

Non-condensing boilers are slightly cheaper (by around 100-200), less complicated, and well understood by most plumbers.

Condensing boilers are different in several ways:

  • The condensed steam is hot and slightly acidic; it has to be removed safely from the boiler and plumbed into a suitable drain. This means stainless steel or aluminium construction, rather than ordinary steel.

  • The buoyancy of the exhaust is lost when the steam has condensed, so a fan is needed to remove it.

  • A larger heat exchanger is needed than in a conventional boiler, and it needs to be more efficient.

  • The exhaust produces a visible plume of vapour so the flue needs to be sited to avoid it causing a nuisance.

  • Condensing boilers contain extra components and require more expertise from the plumber.

    There is very little information on the internet about gas boiler performance or longevity. Most of what pretends to be objective is little more than sales literature or government propaganda.

    For example, the government says "condensing boilers can save up to 37% on gas bills".

    After the recent expenses scandal, I guess no-one is going to believe any government figures for a while.


  • "We have had a condensing boiler for five years. When we had it fitted we had difficulty finding anyone willing to do the work. Since then nothing but a catalogue of faults."

  • "Plumbers frequently have to pay repeat visits and have difficulty diagnosing faults". (....Not surprising since the technology is relatively new - Ed. )

  • "Some plumbers won't even come out when they hear it's a condensing boiler. The plumber we pressed into doing the job said they were always going wrong".

  • "Finally, we called out British Gas on a fixed price visit. The engineer fixed it all".

  • "We have had one for several years; no problems at all, and our fuel bills have gone down slightly".

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