Flue condensate eroding concrete?

[^woody^]

I looked at a property recently where a boiler flue (not combi) was exiting a wall above a concrete canopy - which was about 75mm thick

Directly below the outlet, the concrete canopy had a chunk missing. The missing bit looked like it has been hit and chipped off, but the edges of the concrete are not clean like a chip, but more smooth like erosion.

The flue pipe does not seem that old, maybe a year or two, so I wondered what were the chances of the cause being due to the acidic flue gasses condensing and dripping on to the concrete below?

 

[gigz]

If its a condensing boiler the flue should be falling back to the boiler so any condensation goes back into the boiler and out through the condense pipe to a drain.

 

[gas4you]

Standard efficiency boilers would have the flue slightly downwards to the outside, so any 'condesate' would run out a possiby causewhat you have seen.

Officially it would not be classed as condensate as it is probably not a modern condensing boiler.

It is very common to drive around and see many properties with staining all down the wall from older boilers due to this.

 

[keego]

If its a condensing boiler the flue should be falling back to the boiler so any condensation goes back into the boiler and out through the condense pipe to a drain.

That's the theory!. The design of some of these flues mean you will get a drip off it even when fitted to the letter of the MI's, I've had some where I had to put it at such an angle it looked bleedin awfu, so the choice was fit it right & put up with it dripping or fit it so it looked like a dogs dinner.

 

[kevindgas]

OP yes it can cause failure of concrete even the plumage. haven't seen any above like you describe but have come across 3 or 4 where the ground below is damaged.

dripping end of flue can sometimes be cured by tweeking the lip a MM or 2 along the lower half to for a very tiny lip. Ideal icos/isar/evo's are prone to this problem

 

[Agile]

Sometimes there is a small moulding lip which needs to be filed away to let the condensate to run back.

Alternatively its sometimes necessary to put a couple of mm of sealant to form a ridge at the end.

Tony

 

[TicklyT]

It could also be helped along by rainwater dripping off the flue terminal, with the drips always landing on the same spot.

Once there's a little bit of a depression holding a few drops of water, a few good frosts would help the erosion process along further.