Condensing Boilers FAQ

Condensing boilers FAQ – Some common questions about condensing boilers

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%-90%).

1. Are condensing boilers unreliable new technology?

Condensing boilers have now been in use for 20 years and are reliability – indeed most of the components are also used in non-condensing (conventional) boilers.

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-sizing radiators. Larger radiators will allow slightly cooler water to return to the boiler and can increase the efficiency by a further 3%. However this is not considered to be cost effective and is often impractical.

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-condensing boiler is a drain for the condensed liquid which is like a plastic overflow pipe.

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-condensing boilers cannot be seen due to their high temperature. The cooler flue gases from a condensing boiler produce a plume which can be seen. Therefore care should be taken locating any flue terminal to avoid the visible plume being a nuisance to neighbours however numerous flue options are available.

8. Do condensing flue products kill plants?

Plants thrive on carbon dioxide!

9. Aren’t they more expensive?

Yes but the price difference has continued to reduce and is offset by the saving in fuel bills. Condensing boilers are the most efficient boilers available – the more efficient the boiler is, the less fuel it uses, the less carbon dioxide it produces and the less it costs to run.

See the SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) website for some useful facts and figures.