Steam from Gas Boiler Discharge

[Hysteresis]

Some of my neighbours have had new gas boilers fitted and they seem to discharge a lot of steam from the boiler discharge vent. Mine on the other hand does not discharge any steam what so ever, and never has. My boiler is 16 years old and I have never had a problem with it.
So the question is, Why do these new boilers discharge steam?
Logically (?) I would say that any steam must originate from water vapour in the gas supply or a leak in the heat exchanger discharging water into the combustion chamber. The water vapour in the gas supply would be evident in my boiler also if this were the source, but I don't have this steam evident. So the water in my neighbours discharge must be from elsewhere.
I think my logic is flawed somewhere but it begs the question, Is no steam in the discharge evidence of an inefficient boiler or vice versa and my boiler is more efficient than my neighbours new boilers?

 

[Newboy]

Is no steam in the discharge evidence of an inefficient boiler or vice versa and my boiler is more efficient than my neighbours new boilers?

The water vapour is a product of combustion and, on a newer boiler, leaves the flue at a lower temperature than older boilers. The lower flue gas temperature of your neighbour's boiler means that more of the heat generated by combustion is being recovered within the boiler and used to heat the house. Your higher temperature flue gas means that your boiler is not recovering as much of the heat generated by combustion and you are wasting heat by heating the outside air.

 

[Terrywookfit]

CH4 + 2 O2 = CO2 + 2 H2O

 

[Ted777]

Sorry to jump on your thread...

This is something that always puzzles me, So when the boiler is pluming white steam, that means the boiler is in condensing mode and throwing the condensed water into the secondary heat exchanger and then sending it through your radiators, when the boiler gets the return of hot water from the radiators above 60c it won't go into condensing mode and throws that excess heat out the flue which looks invisible? That's the wasted heat? I have my boiler temp set for central heating at about 60c as my home gets to hot when it's set to max. I can only tap the heating outlet pipe with my finger as it's so hot, yet the heating return pipe I can hold it as it's only warm meaning my radiators have took the heat and pushed it into the rooms, returning I'm assuming a lot under 60c, which when I look at my flue outlet pipe it's pluming away. Does that mean I'm using my boiler the most efficient way?

 

[Hysteresis]

Thanks you so much Newsboy and Terrywookfit. It takes me back to my long forgotten Grammar School days which in my defence was around 60 years ago. The Chemical Balance equation was particularly useful.
It rather begs a few more questions. When I questioned myself on the lack of a steam plume from my boiler I wrongfully thought that I had a condensing boiler installed in that the heat recovery was condensing the majority of the water vapour from the discharge gasses. The reason for this conclusion was that if the discharge was at a too high a temperature and therefore containing the water vapour, the plume would become visible when the exhaust cooled in the atmosphere and as such the plume become visible at say two feet from the discharge. As this is not evident I assumed my boiler was condensing and therefore recovering the discharged heat. Clearly I am wrong with that assumption although it still puzzles me. It also suggests to me that the modern condensing boilers are not working as well as claimed as if they were recovering ALL of the waste heat, there would be no steam plume visible as ALL of the water vapour would have been condensed.
The Chemical Balance equation certainly explains the source of the H2O and thanks so much for the reminder.

 

[bernardgreen]

It also suggests to me that the modern condensing boilers are not working as well as claimed

The claims are made based on results of trials conducted in conditions that are ideal for the boiler nut maybe not ideal for the person in whose home it will be installed.

If the water arriving at the boiler to be heated is hotter than the dew point ( the temperature at which water vapour becomes liquid ) then the simple boiler cannot operate in condensing mode as it cannot cool the combustion products below the dew point.

Some additional recovery ( condensing vapour into liquid ) can occur in the concentric flue where the incoming air in the outer tube is warmed by the hot flue gases in the inner tube.

 

[denso13]

What's this BS about 4 year old posts?

It goes against the site rules, do you think they are BS?

A study for something that takes longer than a few minutes is invalid?

No, just start a new thread. It just causes confusion and people responding to earlier old posts in a thread as @Harry Bloomfield has just done.