Condensing boilers FAQ -
Condensing central heating boilers are the most energy efficient boilers available.
All gas boilers fitted in both new and existing homes must be condensing boilers
with either an ‘A’ or ‘B’ efficiency rating (A= greater than 90%, B= 86%-
1. Are condensing boilers unreliable new technology?
Condensing boilers have now been in use for 20 years and are reliability -
2. Are they only efficient when condensing?
They will ALWAYS be more efficient than a new regular boiler whether in condensing mode or not. They can be up to 10% to 15% more efficient than a modern conventional boiler and up to 30% more efficient than older boilers so the energy saving and the impact on your fuel bills can be significant.
3. Must radiators be oversized?
There is only a marginal benefit from over-
4. Can condenser boilers be fitted to existing systems?
They can be fitted to most new and old systems. Normal good practice must be followed which will include flushing of system and adding an inhibitor. As with any replacement boiler, an assessment of the effectiveness of the control system and type of hot water cylinder, should also be made.
5. Are condensing boilers difficult to install?
The only real difference from a conventional non-
6. Is the condensed liquid a problem?
Up to 1 litre of condensed water per hour is produced. This has a pH of about 5 which is between rain water and cola. The condensed liquid is disposed of through a condense pipe connected to the drainage system.
7.What about pluming from flue?
The flue gases produced on non-
8. Do condensing flue products kill plants?
Plants thrive on carbon dioxide!
9. Aren't they more expensive?
Yes but th price difference has continued to reduce and is offset by the saving in
fuel bills. Condensing boilers are the most efficient boilers available -
See the SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) website for some useful facts and figures.




