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New cond'ing boiler; what an extra-ordinary waste of heat to outside; why?

Mike Reed

Mike Reed

pfm Member
Had our new Vaillant boiler for a couple of weeks now, and noticed clouds of white emissions billowing across the patio. I know this is normal (?) as when my 3 or 4 neighbours turn theirs on, I could see similar clouds of emissions. What I didn't expect was that these are hot (I put my hand up to the outflow pipe).

Our old Potterton hardly emitted anything that visible, but I never tried to feel the heat(because it wasn't really visible to any degree).

I think that the new emissions are condensation, whereas the old were not; that's the limit of my understanding. Regardless, with a new boiler, I didn't expect to heat the outside to such a degree. I thought that condensing kept that heat inside, and I cannot understand the waste of energy in this technological age.

Anybody got any take on this?
 
Mike Reed said:
Had our new Vaillant boiler for a couple of weeks now, and noticed clouds of white emissions billowing across the patio. I know this is normal (?) as when my 3 or 4 neighbours turn theirs on, I could see similar clouds of emissions. What I didn't expect was that these are hot (I put my hand up to the outflow pipe).

Our old Potterton hardly emitted anything that visible, but I never tried to feel the heat(because it wasn't really visible to any degree).

I think that the new emissions are condensation, whereas the old were not; that's the limit of my understanding. Regardless, with a new boiler, I didn't expect to heat the outside to such a degree. I thought that condensing kept that heat inside, and I cannot understand the waste of energy in this technological age.

Anybody got any take on this?
Click to expand...
I suspect that because your exhaust gases are colder they are closer to the dew point when they hit the cold air. when the exhaust gases are hotter they don't generate fog because the gases are too hot and are dispersed before they cool down. I suspect that had you put your hand in the exhaust of the old boiler you would have got a burn.
 
That is perfectly normal.
The exhaust already goes through a heat exchanger (as you say, the 'condensing part') to take out the vast majority of the heat left over from when it was burnt initially.
It's not actually that hot, more akin to us breathing out.
You will have (presumably) a condensate 'drain pipe" leading from below the boiler to a local drain. the water from the heat exchange unit gets pumped out through this at regular intervals.
**Note** be aware - during very cold / freezing conditions, this condensate drain can freeze solid, and the boiler will flash a fault, and not work.
A kettle of hot water over this pipe soon has it back working again, and the pump to expel the condensate goes into overdrive for a few minutes.
Ours sounds like a dinosaur waking up with a bad cold when this happens.
 
yes all perfectly normal . we have huge wafts of white steam wafting across our garden from the neighbour who kindly fitted their flue 300 mm or so from our border . they always have been very thoughtful :eek::eek:
 
Mike Reed said:
Had our new Vaillant boiler for a couple of weeks now, and noticed clouds of white emissions billowing across the patio. I know this is normal (?) as when my 3 or 4 neighbours turn theirs on, I could see similar clouds of emissions. What I didn't expect was that these are hot (I put my hand up to the outflow pipe).

Our old Potterton hardly emitted anything that visible, but I never tried to feel the heat(because it wasn't really visible to any degree).

I think that the new emissions are condensation, whereas the old were not; that's the limit of my understanding. Regardless, with a new boiler, I didn't expect to heat the outside to such a degree. I thought that condensing kept that heat inside, and I cannot understand the waste of energy in this technological age.

Anybody got any take on this?
Click to expand...
I think when you see the reduction in your gas consumption ( thought not the overall cash) you will be very pleased Mike. I couldn’t believe how much gas we saved when we ditched a huge floor standing boiler for our first WB Greenstar 22 years ago.
 
hifinutt said:
yes all perfectly normal . we have huge wafts of white steam wafting across our garden from the neighbour who kindly fitted their flue 300 mm or so from our border . they always have been very thoughtful :eek::eek:
Click to expand...
Water vapour not steam.
Steam is an invisible gas…
 
Water vapour is a vapour (often termed a gas but rather loosely if it's below the critical temperature, some 300 odd degrees C) and is invisible. This phase is called steam. The plume you see is liquid water that has condensed from the vapour phase as it hit the air outside - just like when you can see you breath on a cold day.

In a vapour phase (at normal pressures) the molecules are far apart from each other - by definition - you can't see individual molecules with the naked eye.
 
Water vapour means rejoice your boiler is condensing the flue gases and getting every last possible iota of energy out of your fuel. See if you can get the maximum flow temperature in your boiler down to 55 degrees to ensure this happens all the time. Might be able to do this yourself if you have the manual
 
timH said:
Water vapour means rejoice your boiler is condensing the flue gases and getting every last possible iota of energy out of your fuel. See if you can get the maximum flow temperature in your boiler down to 55 degrees to ensure this happens all the time. Might be able to do this yourself if you have the manual
Click to expand...

Wouldn’t recommend running the boiler at 54 degrees in this weather unless the OP has amazing insulation.
 
Sonority said:
That is perfectly normal.
The exhaust already goes through a heat exchanger (as you say, the 'condensing part') to take out the vast majority of the heat left over from when it was burnt initially.
It's not actually that hot, more akin to us breathing out.
You will have (presumably) a condensate 'drain pipe" leading from below the boiler to a local drain. the water from the heat exchange unit gets pumped out through this at regular intervals.
**Note** be aware - during very cold / freezing conditions, this condensate drain can freeze solid, and the boiler will flash a fault, and not work.
A kettle of hot water over this pipe soon has it back working again, and the pump to expel the condensate goes into overdrive for a few minutes.
Ours sounds like a dinosaur waking up with a bad cold when this happens.
Click to expand...

Excellent post.
 
timH said:
Water vapour means rejoice your boiler is condensing the flue gases and getting every last possible iota of energy out of your fuel. See if you can get the maximum flow temperature in your boiler down to 55 degrees to ensure this happens all the time. Might be able to do this yourself if you have the manual
Click to expand...
Does this apply to condensing boilers, or just combi boilers?
 
We’re sticking with 55 as long as we can. Probably have to relent during the coming week though
 
timH said:
We’re sticking with 55 as long as we can. Probably have to relent during the coming week though
Click to expand...

It’s fine as long as the outside temperature is well above freezing, you have large rads and really good insulation but otherwise it wouldn’t be me, condensing boilers are very efficient even when they’re not condensing
 
I reduced the flow temperature on my boiler to 60% last week after having to do some research on how (couldn't see how to adjust the return temperature, I'm wondering if that's automatic). Radiators are taking longer to heat but that's not really a problem.
 
kensalriser said:
I reduced the flow temperature on my boiler to 60% last week after having to do some research on how (couldn't see how to adjust the return temperature, I'm wondering if that's automatic). Radiators are taking longer to heat but that's not really a problem.
Click to expand...

You can’t adjust the return temperature (well you can but I wouldn’t advise it) larger rads means the return water is cooler going back to the boiler what you’re looking for is a 20 degree temp differential so 54 out and 34 back or 80 and 60 back also turn all TRVS up full.
 
Our boiler is a Viessman with a modulating room thermostat and I’ve also got the Viessmann app on the phone and iPad. Currently the boiler is on with a flow temp of 55 and the burner is at 13.1% modulation. Room temp is at 22 but lower down near the floor its about 19. Quite comfortable at the moment. Loop app picks up from smart gas meter and tells me I’m spending about £6 a day(january was about £7 a day
 
Here’s mine, I’ve an outdoor sensor on a north west facing wall and weather compensation too the programmer is Open Therm ie it runs the boiler flow temperature vis the outside temperature and a climatic curve of 1.5.

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Bob McC said:
Water vapour not steam.
Steam is an invisible gas…
Click to expand...
No its not. Steam is that cloudy stuff you see when water is boiling in a kettle. Look closely and you'll see that immediately after the spout it is clear and you can see through it and thats water as a gas at boiling point. A little further out and you see cloudy steam Its actually the same stuff as the clouds we see in the sky. Both steam and clouds are a colloidal suspension of a liquid water within a gas.

If colloids are new to you think how you would classify things like butter, whipped cream and smoke. Are they in a solid, liquid or a gas phase? These are actually colloids a suspension of one phase in at least one other.

We can't see a gas because our eyes can't detect individual molecules but we can see tiny droplets/particles that then scatter light as a mist or cloud.

Vapour is another name for the gas phase so we can't see it.

Teach mode off.

DV
 
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