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Discuss Condensing mode when does it happen in the Central Heating Forum area at

  1. howy1

    howy1 Member

    Hi all , I live in new build house with condensing boiler and unvented cylinder , what I would like to know is if my boiler is ever in condensing mode and how I could find out.
    I have read that the return needs to be around 55 degrees c to reach dew point which I guess is when the residual energy is taken from the flue gases , I would like to understand how this works . Thanks in advance.
  2. SJB060685

    SJB060685 Top Contributor!!

    You’re pretty much there. The return temp needs to be at that temp to extract the last available heat possible enabling the gases to condense. If the temperature were higher due to oversized boiler or poorly piped up system/return etc etc then condensing mode won’t happen and the boiler will be less efficient.
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  3. Best

    Best Trusted Plumber

    But in this cold weather, with temperatures below freezing, you might need to turn your boiler stat up higher than normal and this will mean the boiler will not reach full condensing mode.
    Particularly if your radiators are undersized.
    Not to worry too much, as a condensing boiler will still condense and extract more heat from fuel than an old boiler would.
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  4. John.g

    John.g Active Member

    To get the full condensing benefit the return water should probably be -40/45C in order to get the flue gases as low as possible, however as stated elsewhere yor will still get 5 to 7 p.cent more efficiency than that of a non condensing boiler as the flue gas temperature will be - 100 to 120C lower because of the second heat exchanger fitted. The full condensing effect, depending on type of fuel, should increase the efficiency by a further 6 to 9 p.cent.
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  5. Matchless.plumb

    Matchless.plumb Trusted Plumber GSR

    What boiler have you got?
  6. howy1

    howy1 Member

    Thankyou all for your responses , we hear so much about alleged modern money savers and its good to know how it works and what to look for regards howy
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