Condensing boilers in condensing mode

Andy From Sligo

you know the saying that Condensing boilers work most efficiently when they are working in condensing mode and the temperature is between 50-55c - are they talking about the temperature of the return water pipe coming back from the rads or are they talking about when the Flue temperature is 55c and under its working in condensing mode?

I just watched a video on youtube that said conventional oil boilers start off with 300c in the combustion chamber and baffle area and have a whopping 250c of heat coming out of the flue in other words you loose 250c out of the flue but on a conventional oil boiler you only loose 55c out of the flue on a Condensing boiler! - I find that amazing :eek: - I knew condenser boilers were better over conventional oil boilers but i didnt realise they were that efficient!!

So if you have a condensing boiler and you stuck a thermometer up the flue - is it the case you want your flue temp not to exceed 55 degrees c - and if it is more than 55c will it not work in condensing mode? - is that what they mean?

Tom44

Flame temperature in the combustion chamber is about 1100°c

The less of that out the chimney = house getting it instead. = better boiler.

DGOBS

What they mean is at below 55ºC (the dew point) is when the water vapour in the flue gas returns to water, and releases the 'latent heat' it used to remain in gaseous form, and the boiler absorbs this heat in the condensing heat exchanger.

Even when a condensing boiler is not in condemning mode, it is still more efficient than a conventional boiler due to the extra internal surface area of the heat-exchangers in complain to a conventional boiler.

Andy From Sligo

DGOBS wrote: »

What they mean is at below 55ºC (the dew point) is when the water vapour in the flue gas returns to water, and releases the 'latent heat' it used to remain in gaseous form, and the boiler absorbs this heat in the condensing heat exchanger.

Even when a condensing boiler is not in condemning mode, it is still more efficient than a conventional boiler due to the extra internal surface area of the heat-exchangers in complain to a conventional boiler.

Ah right thank you. So the actual flue temp has to be under 55c not the return water pipe from the rads, is that what they mean?

So you could have 60c on the return water pipe and 50c flue temperature and the boiler will be running in condensing mode yes?

antoinolachtnai

If the return water pipe is 60C and the flue temperature is 50C, then how would heat transfer from the secondary heat exchanger to the water? Traditionally, heat moves from the warm area to the cold area. No dice, I don't think this is going to work!

Andy From Sligo

antoinolachtnai wrote: »

If the return water pipe is 60C and the flue temperature is 50C, then how would heat transfer from the secondary heat exchanger to the water? Traditionally, heat moves from the warm area to the cold area. No dice, I don't think this is going to work!

ah yes I see, right thanks.

Looking at the technical data for our boiler which is grant euroflame 70-90 condensing if it had the correct 80'EH nozzle in it (but it hasnt , its got a 60'S in there instead) then the flue temperature should be 85c-90c

So when it says its working in 'condensing mode' - that must mean the return water pipe from the rads going back to the boiler/condensing unit must be under 55c to be working in condensing mode/ie most efficient - Have I got that right now?

antoinolachtnai

As I understand it yes. There may be a little graph in the installation manual which shows how efficiency and return temperature are related.

Andy From Sligo

antoinolachtnai wrote: »

As I understand it yes. There may be a little graph in the installation manual which shows how efficiency and return temperature are related.

many thanks