Steaming

[Warwick]

A couple of years ago we had a Gas condensing boiler fitted.

The plumbers pointed out that due to the efficiency it vented steam rather than extremely hot air. I've checked up on this claim and it seems accurate.

Tonight someone called the fire brigade to report that there was smoke pouring out of our roof. They turned up, investigated, asked if we had a high efficiency boiler. They're getting lots of calls from people who see thick clouds pouring out out roofs.

Has anybody any ideas how I might prevent this happening again? Would a mesh ball mounted on the outlet help? Some kind of fan?

Warwick-- long lurking

[Rupert]

The whole idea of a condensing boiler is that rather than pumping out really hot gases (water vapour+ CO2), these hot gases heat the incoming air intake used by the gas burner. Consequently the gases that are emitted are cooler and form a cloud of white water vapour the moment they leave the flue. In an old fashioned non condensing system the very hot gases left the flue and did not start to form clouds until they were several metres from the building. Putting a mesh ball on the outlet will not make an difference.

[John Rumm]

yup... will be most visible on still, dry, cold nights/days

Novel...

Yup, educate the neighbours! ;-)

not really.

A long vertical flue extension would allow still more water to condense out (and it would need an additional condensate drain point in the flue to deal with it in some cases) and reduce the visible plume a bit. Some people even run the flues up chimneys in a liner so that the "smoke" looks less out of place.

[sPoNiX]

A big sign saying "My house is not on fire" planted in the front garden?

In all honesty I don't think there's a lot that can be done. However, it's good to know that one of the neighbours cares enough to report a potential fire in your house.

sponix

[Christian McArdle]

Well it isn't really steam, but close enough!

Make sure the neighbour knows it wasn't a problem.

Explain to your neighbours that modern boilers produce visible plumes. Indeed, in this weather my mother's non-condensing boiler is pluming.

Nope. Only education. Most efficient boilers will plume in some conditions. Think of power station cooling towers.

Christian.

[Sadly]

I can see that one coming back to bite one day (when the house really is on fire, and no one calls the fire brigade!)

[Dave Plowman (News)]

Good grief.

[Christian McArdle]

It's no great surprise. In the right weather some of these plumes can be of great density. Condensing boilers are still not very common, so many will not be used to it.

Christian.

[Rick]

It's doing what it should be ... just much more prominent in cold weather.

Just tell your neighbours that this is correct.

[Andrew Gabriel]

I did warn my neighbours when I fitted one a few years ago. What I didn't think to do was to warn the new neighbours when their house changed hands, so the new neighbours came round to investigate when they saw it happen and I wasn't in. The flue isn't visible from their property, but the plume is where it rises above a single storey section.

[Autolycus]

Eh???? No - the heat exchanger is designed to cool the flue gases more efficiently, thus transferring more energy to the water. By cooling them to the point where condensation occurs, the enthalpy of evaporation (aka latent heat) is also available as useful energy.

post hoc but not propter hoc

yup

Hmmm. Don't they disperse too much to leave a visible cloud before they get "several metres" away? Even moderately efficient non-condensing boilers will plume to a degree in the right weather conditions, often quite close to the flue.

Can't argue with that one.

"A friend" recently fitted a plume management kit to a new Glow Worm condensing combi - not much more than a rather expensive length of plastic pipe and a couple of elbows - but it does at least make the plume emerge a few feet above the roof, while keeping the air inlet close to where the flue goes through the wall.

[Warwick]

That's the second time I've had that point made to me. I promise not to make the same error ever again.

Warwick

[Warwick]

*yadda*

OK Thank you.

As I guessed, About the only thing I could do would be to add a couple of feet of extra flue so that it would be visible above the roofline and then I'd need to think about maybe needing a drainpoint and securing a

3' flue. I can't redirect it up a chimney since the house was built in 1981 and doesn't actually have a chimney (not even a fake useless one). I thought a fine mesh ball might function as a condensate catcher, but that'd reduce the plume by maybe 30% until it warmed up.

We only have one new set of neighbours over the road and they're a very nice couple so I think I'll ask them if they were the concerned ones.

Warwick

[Suz]

But not enough for the twit to walk over and knock on the door...