Condensing oil boiler plume question.

[mikrt]

Hi,

I'm still getting used to oil after converting from wood pellets.

I'm fairly happy with it's operation, but slightly adjusting temperatures to get as low return temp, while keeping house & DHW hot enough.

Anyway, I've always believed that when the flue had a white plume exiting, it was a good thing.

However I've just read this https://www.theheatinghub.co.uk/why-our-condensing-boilers-do-not-condense

where about half way down, the opposite is stated.

Are they correct? If so, I'll need to rethink my temperature settings again.

Thanks for reading.

 

[SJB060685]

Water vapour is transparent, if you are seeing plumes of white this says the water has condensed and has caught the light, giving it this whitish, non transparent appearance.
Many things can affect whether a boiler condenses or not, ultimately stemming from the return temperature at the boiler. Ideally the system should be balanced to a delta t of 20°c with the boiler flow set about 70 °c.
Another thing to bare in mind is the dew point for condensation is directly affected by the CO2% of the combustion. So you want a system suitably sized, installed and balanced, as well as the burner being commissioned properly.

 

[mikrt]

Water vapour is transparent, if you are seeing plumes of white this says the water has condensed and has caught the light, giving it this whitish, non transparent appearance.
Many things can affect whether a boiler condenses or not, ultimately stemming from the return temperature at the boiler. Ideally the system should be balanced to a delta t of 20°c with the boiler flow set about 70 °c.
Another thing to bare in mind is the dew point for condensation is directly affected by the CO2% of the combustion. So you want a system suitably sized, installed and balanced, as well as the burner being commissioned properly.

Thanks for that,

Some of that went over my head, but I have faint whitish cloud from my flue when running, a set point of 55 oC +/- 1 @ 325L thermal store, with a supply temp of 57 oC and return of 45 oC. The recirc pump between boiler & TS is on it's slowest setting.

I was pleased with that, but after reading that website and your reply, now I'm not so sure.

I can't think of anything left to adjust, unless you can suggest something, or am I just on the limit of what I could hope to get?

 

[SJB060685]

With thermal stores you need to heat the water to a higher temperature ready for the hot water draw off, usually these are set to a higher set point.
A return temperature going back to the boiler of 45°c is definitely going to allow the boiler to condensate and as I said above the white pluming suggests that is happening. However too low a return temperature can be bad news for oil condensing boilers and may need to be mixed to maintain a minimum return temperature, you would have to speak to the manufacturer of your oil boiler and find out what they require.

 

[mikrt]

With thermal stores you need to heat the water to a higher temperature ready for the hot water draw off, usually these are set to a higher set point.
A return temperature going back to the boiler of 45°c is definitely going to allow the boiler to condensate and as I said above the white pluming suggests that is happening. However too low a return temperature can be bad news for oil condensing boilers and may need to be mixed to maintain a minimum return temperature, you would have to speak to the manufacturer of your oil boiler and find out what they require.

Thanks again. The dhw is blended down to 50 oC, and ufh only needs 38 oC. Not getting cold yet, we'll see in a few weeks maybe 😨

 

[SJB060685]

Thanks again. The dhw is blended down to 50 oC, and ufh only needs 38 oC. Not getting cold yet, we'll see in a few weeks maybe 😨

Ah, I must of missed you mention that above.
As I said my primary concern is your return temperature not being too low, some oil boilers don't fare well if this is the case and you can get corrosion in places. I believe and don't quote me on this but Grant boilers recommend a minimum of 50°c return to prevent this.

 

[mikrt]

Ah, I must of missed you mention that above.
As I said my primary concern is your return temperature not being too low, some oil boilers don't fare well if this is the case and you can get corrosion in places. I believe and don't quote me on this but Grant boilers recommend a minimum of 50°c return to prevent this.

Thanks again. It is a grant, but 40 is the min 👌

 

[SJB060685]

Well thanks as I didn't know that was the figure. By the sounds of it its probably at optimum performance.