Downsizing a c26

cruiser202006

Commissioning a boiler in the morning. Plumber installed a c26 as homeowner plans to build an extension in de next year or two. I've calculated that I need 17kws. If I fit a t1 blast tube and a 0.5 80 end nozzle at 9 bar would it be ok? I'm guessing there probably the same boiler anyway

Wearb

If you go below Firebirds suggested firing rate, you are probably going to loose out on efficiency. You may not be doing your customer any favours by under-firing it. It might be as well to fire it at its lowest rate and put up with the cycling.
You should talk to Firebird about it.
I have a C44 that I look after and it is way underfired and is working well, but I have no way of knowing how efficient it is over the season by underfiring it like that.

You will probably void the warranty if a warranty call has to be made.

cruiser202006

Wearb wrote: »

If you go below Firebirds suggested firing rate, you are probably going to loose out on efficiency. You may not be doing your customer any favours by under-firing it. It might be as well to fire it at its lowest rate and put up with the cycling.
You should talk to Firebird about it.
I have a C44 that I look after and it is way underfired and is working well, but I have no way of knowing how efficient it is over the season by underfiring it like that.

You will probably void the warranty if a warranty call has to be made.

Ya maybe I'll ring firebird technical about it in de morning first thing. Just to cover myself!!

Wearb

cruiser202006 wrote: »

Ya maybe I'll ring firebird technical about it in de morning first thing. Just to cover myself!!

I'm interested in their reply. Let us know their answer, though I expect that they will say stick to MIs.

cruiser202006

Wearb wrote: »

I'm interested in their reply. Let us know their answer, though I expect that they will say stick to MIs.

Will let you know tomorrow evening! Just by looking at manual de c20/c26/c35 seem to have the same shell. Never seen a c20 but baffles from a c26 fit a c35. Will definitely doublecheck with firebird first

Dtp1979

They told me before that if its undersized then it'd produce a lower temp in the combustion chamber and Would lead to condensation. I think they called it flame chilling. I could be wrong on that one

Wearb

Dtp1979 wrote: »

They told me before that if its undersized then it'd produce a lower temp in the combustion chamber and Would lead to condensation. I think they called it flame chilling. I could be wrong on that one

If the boilers (c20 and c26) are the same and if the only difference is the burner head, it would be nice to know. They look the same, but there could be some discreet difference.

agusta

In my opinion the c20, c26 and c35 are the same boiler with a small difference between each one.They all use the same tube baffles.The plate baffles are different in each boiler.Even though a baffle from a c20 will fit into a c35,it cant be used in a c35

cruiser202006

Rang firebird technical department this morning but they mustn't like ringing people back! So installed a .6 80 es at 9 bar

Wearb

cruiser202006 wrote: »

Rang firebird technical department this morning but they mustn't like ringing people back! So installed a .6 80 es at 9 bar

Poor Customer service.

That configuration isn't too far off its low firing rate.
They should be happy with that. I would still like them to confirm it though, just to validate warranty.

DGOBS

Remember guys, it's a lot to do with surface area, and temperature absorption, stick the the manufacturers instructions, don't deviate.

Don't you thing if a manufacturer could have made the boiler with a wider usage range it would be better for them?
I more versatile product (better sales) lower manufacturing costs as no need for different machine setups, lines, parts, etc.....

What they meant about flame chilling is, as you have less input vs surface area, you will obtain a lower flue gas temperature, and being condensing in the mild steel section of the appliance, which will rot the chamber.

Wearb

Been thinking about this underfiring of the C26 or any other HE boiler for that matter.
My thoughts are that the limited MI firing range of those boilers has more to do with getting a good boiler efficiency rating than condensation in the heat exchanger.
I do understand that condensation can and does happen in the mild steel heat exchanger, but with a HE boiler it would have to be underfired a lot for this to happen, because of the increased return flow temp in the steel heat exchanger.
Now if I am correct then it is possible to safely (leaving efficiency to one side for the moment) underfire.
If so, then is it better to underfire an oversized boiler or to fire it at its lowest MI rate and let it cycle often.
Boiler manufacturers surely have those figures from their testing.

Anyone here know of any of those engineers who would answer that?

DGOBS

Remember flame chilling will lead to high CO also.

Wearb

My understanding of flame chilling is that it is caused by too much combustion air or flame impingement. Neither of those would occur when underfiring, so long as proper combustion is setup i.e. correct air to fuel ratio, correct burner head and correct nozzle pattern.

DGOBS

Flame chilling may occur also where there is too low a heat input vs the boilers ability to absorb heat (surface area), in certain cases this can draw the flame too

Wearb

I can understand how condensation can occur in that instance, but flame chilling is a step too far for me. That doesn't mean that I doubt your understanding of it, but I think I need to give it more thought and study.
I know that we shouldn't underfire a boiler, but there are times when we come across ones that are way oversized. I just wondered whether it was best to stick to MIs and let it cycle, or go below MIs and meet the heating requirements half way.
I know the safe bet is to stick to MIs, but I do wonder about these things sometimes.

DGOBS

I understand your thought process, but once we depart from MIs, then we void warranty and take complete responsibility for any outcome (as we are the competent people)