Condensing boilers-contentious question

[Agile]

Well said paul . Amazing how many people actually believe this 35% gas saving.

The saving in using a condensing boiler in full condensing mode is 12% or less.

BUT because a condensing boiler has lower flue temperatures ( 50° compared with 130°+ ) it is always more efficient than a non condensing.

This figure of 35% ( actually quoted as "up to 35% ) in in some British Gas sales material and probably others as well. But that is based on "worst case" of an old back boiler or a massive cast iron boiler and not a modern copper heat exchanger boiler like virtually all combi boilers.

The saving from a non condensing combi to a condensing combi would be about 15%, not massive but still useful. However, its not going to give a payback by just changing to a condensing boiler unless there are other reasons to change like end of life or expensive breakdown.

All modern condensing boilers should last at least 10 years. There are many old Glow Worm condensing boilers ( Ulitmate ? ) which are now about 15 years old and still work for many years without servicing.

Tony

 

[Paul Barker]

"how long they last" is almost always down to the cost of parts, alone. Very few corrode much, and most of the parts aren't too hard to change.
(There are exceptions of course!).

yes well now it seems I can't turn down Ideal Isars. SPent the afternoon taking one off the wall to change the expansion vessel, then noticed the inner flue where it joins the manifold had corrded away so it has been leaking condensate onto the display board which understandably is bust. So when the parts arrived it's just put it all back together reseal the where the flue goes through the wall, reglue the condensate which fell apart reattach the prv outlet, and maybe then the job can be closed down and I earn £20 for the whole of Saturday afternoon and a couple of hours next week.

Any jobs going in IT?

I mean when have I ever said on here what a great boiler Ideal Isar is? Yet an organisation which should be able to spot a suitable boiler to sell which they would become responsible for maintaining has littered the country with them and now expect their poor engineers to keep them alive.

If I ran a large heating industry company the last boiler on this earth I would install is the Isar.

All you people who are envious of us want your heads examining.

 

[Agile]

Hang on! Give it a chance, you have only been there about three weeks!

I have this expectation that when you turn up in your nice BG van and your BG blue shirt the customers have a high degree of confidence that you can fix it!

Luckily for them, in your case, you really can! ( Pity about some of the others though! )

Tony

 

[nickso]

presumably when you turn up in your manky check shirt they thank their lucky stars for your 100% repair record?

 

[oilman]

The saving from a non condensing combi to a condensing combi would be about 15%,....

This is the theoretical maximum, only available if the steam in the flue gases is completely condensed inside the boiler. We know from the obviously visible plumes from the exhaust that it is not condensing inside the boiler, so the 15% is not achieved.

 

[emscott]

As I thought - controversial!

Thanks for all the replies - interesting reading.

 

[Agile]

The saving from a non condensing combi to a condensing combi would be about 15%,....

This is the theoretical maximum, only available if the steam in the flue gases is completely condensed inside the boiler. We know from the obviously visible plumes from the exhaust that it is not condensing inside the boiler, so the 15% is not achieved.

No thats not the whole cause of the improvement which is about 12% from condensing anyway ( on gas ).

The other improvement, even under non condensing conditions, is from a larger heat exchanger and lower flue gas temperature.

Standard boilers have to keep the flue temperature above about 150°C to prevent condensation and corrosion of the metal flue.

Condensing boilers have flue parts made from stainless steel or plastic and are immune to the slight accidity of the condensate.

Tony