Plume from heating boiler

The reverse is true. Small plume good condensing, large plume no condensing.

Doesn't the visible part of the plume consist of water vapour, and more visible plume means more condensation is occurring?

I notice when I turn the boiler stat up high (75 celsius), there's less visible plume.

In practical terms does the stat on my boiler need adjusting to work more efficiently?

Government messages say turn the boiler down to 60 Celsius but mine is usually set below that and only gets turned up above 60 in cold weather. I am bit sceptical of following their generic advice as I believe it's the return temperature which determines the amount of condensation and I reckon not all systems will have the same temperature drop from what is set on the boiler stat.

Eh? So a non condensing boiler with no plume is the right way to go?

Condensation will leave via the condensate drain, rather than the flue

No. Water vapour is invisible, you're seeing condensed water droplets.

Yes, but you want that to happen inside the boiler. Condensation releases a large amount of energy and you want to keep that inside the house as far as possible. Any water leaving the house in vapour form is wasted energy.

Apologies. I'm getting the terminology mixed up. I should have said "water droplets" instead of "water vapour".

So does that mean a large visible plume (consisting of water droplets) is a good thing?

In other words: my neighbour's large plume indicates their boiler is running more efficiently than mine. Is this a correct understanding?

A year or so ago, there were a lot of suggestions about adjusting a condensing boiler setting that was said to instantly reduce the cost of running the boiler. I don't have one of these, but what was this setting, and how did it magically save money? Were there any downsides, such as loss of microbe cooking?

Steam is invisible, but water vapour isn't.

Of course. The ministry of Truth says so...

Think of a kettle. When it boils (and just before it turns itself off, if you have a modern kettle), there's a plume of 'steam' (droplets of condensed water vapour) coming from the spout. Look carefully at the very base of that plume, just where the water vapour emerges from the spout, and you will see no 'steam'. The 'steam' doesn't form until it meets the cooler air in the kitchen, at which point it condenses and forms fine droplets generally but incorrectly called 'steam'.

Now, if the spout itself was fitted with some form of cooling coil, all the condensation would occur within the spout itself; you'd see no 'steam' emerging from the spout, and the water in the cooling coil would get warm and be recovering some energy. That is what is happening with your boiler, while your neighbour is letting all that energy go to waste by having a large plume of 'steam' being emitted to the atmosphere.

Look out of your window when his boiler is going full blast and feel smug!

No,

On an older non condensing boiler the flue gases can be x3 hotter than on a condensing boiler and so take longer to cool to the required temperature outside for a plume and dissipate before condensing. The reason you don't tend to see the plume on a non-condensing boiler is because you are chucking away so much energy via the flue.

It's just a matter of definition. The atmosphere contains about 0.2% water vapour, but it is invisible. If you were to place a bowl of water under a bell jar and connect it to a vacuum pump so that all the air was pumped out and the atmosphere inside the bell jar was 100% water vapour, it would still be invisible.

What the layman calls 'steam' is a cloud of tiny drops of water, condensed from water vapour as it cools.

No.

The ideal situation is where the condensing is occurring on the heat exchanger dumping heat into the circulating water, and not outside where it's dumping useful energy to the outside environment.

This article on condensing boiler theory seems quite good and I'm pretty sure I understood it some time ago but practice seems rather different and I'm now back to basics!

"Condensing Theory - How Do Condensing Boilers Add Efficiency?"

Bottom line is the whole system needs to be designed for best efficiency and to achieve the best results a more expensive control system is required (external temperature compensation and programmable thermostats etc.).

Hmmm. Mine - a Vaillant Ecotec combi - throws out clouds of the stuff. Keeps triggering the PIR outside light.

It's not set especially high - CH 60c - should I turn it down to make it more efficient?

Possibly.

Can you increase the size of your radiator load?

Owain

Yes, I could - a couple are turned down to about 15C. But that takes me round in circles, heating spaces (kitchen and spare bedrooms) I don't want heating fully. I'll try reducing the temp to say 55C.

snip

Does nobody know the answer to this?