Sooty deposit around MVHR outlet

[pulhamdown]

I have a 1.5 storey T/F house built to near passivhaus standard, built in 2013.  I have a Vent Axia Sentinel Kinetic MVHR unit, which vents out onto the south east facing sloping roof.  All around this vent, there is a sooty deposit on the slates.  I clean / replace the filters every six months, and wash the main filter body in the bath every 12 months.  All are scrupulously dried before reinserting.  There are never any signs of soot on the filters, or on the filter body.   Does anyone have any idea of what's causing this, and if so, what to do to remedy?

[jack]

I recently noticed a very thin patchy area of black dust on the wall adjacent our MVHR outlet. I suspect it's the result of moisture (particularly from showers) condensing onto the adjacent surfaces in cold weather, and providing a habitat for mould. I plan the clean it off with a weak bleach solution and see how long it takes to come back.

Edited to add: you could try Bordeaux mixture. I can't, because my area is painted

[Jeremy Harris]

Could it be a form of black mould?  Just guessing, but the MVHR outlet is always going to be a bit warmer than ambient, plus probably a bit more humid, so perhaps this difference is enough to provide ideal conditions for some form of mould, or perhaps a lichen.

[jack]

1 minute ago, JSHarris said:

Could it be a form of black mould?  

 

That's my guess. I'll take a pic next time I'm up there.

[Alex C]

I get this forming on the timber cladding under the extract vent also. It is black mould.

[pulhamdown]

Firstly, thanks for your replies.  It's always reassuring when others have noticed something similar.  I'll try and get a closer look, as I have a Velux window close by.  So, it sounds as if this is an external issue, and nothing to worry about, other than being a bit unsightly.  Needs cleaning off, though, so I need to get my thinking cap on as to how to access the roof safely.

Thanks

[Jeremy Harris]

If it is a mould or lichen, then copper may work as a way to stop it.  We had a lot of moss and lichen growth on the concrete tiles at our old house, enough to regularly block the gutters and make a mess on the drive.  I found that spraying the tiles with copper sulphate solution was effective at both getting rid of the stuff and preventing it from recurring for two or three years.  There are copper tapes/strips sold to fit along the ridge of a roof to stop moss and lichen growth, and these probably work by leaching out enough dilute copper salts to stop anything growing.  I wonder if a copper plate around the MVHR outlet might work?

 

 

[Ferdinand]

Since it is Friday...

 

1 - Confiscate water pistol.

2 - Shoot Sooty for leaving deposit.

3 - Use water pistol to remove stains.

4 - Return water pistol to Sweep.

 

Edited May 24, 2019 by Ferdinand

[pulhamdown]

1 hour ago, Ferdinand said:

Since it is Friday...

 

1 - Confiscate water pistol.

2 - Shoot Sooty for leaving deposit.

3 - Use water pistol to remove stains.

4 - Return water pistol to Sweep.

 

Crikey!  The sun must be hot down in Notts today!

[Ferdinand]

1 hour ago, pulhamdown said:

Crikey!  The sun must be hot down in Notts today!

 

It is. I am stuck in a south facing room with the blinds closed, trying to find the spec for shades of car paint. Patience is a little lacking.

 

I used to have associations with a local special school, and Matthew Corbett used to come nearly every year with S&S, and they always brought the water pistol, and always shot the Headmaster. Great fun.

 

F

Edited May 24, 2019 by Ferdinand

[Simplysimon]

11 hours ago, jack said:

Edited to add: you could try Bordeaux mixture. I can't, because my area is painted

my bordeaux mixture comes in a 75cl bottle and i wouldn't wash a wall in it.

[lizzie]

Ive just noticed I have this black stuff starting around my mvhr vent.  Its on white render so easily spotted.  Is it Ok just to leave or should I try and clean it off?  I have a metal grille fixed over the vent hole and would need to remove that to get at it. Vent is in the back alley so only visible if you go and look at the grille.

[joth]

We just planning the MVHR location - any suggestions  on how to position the exhaust vents to minimize risk of sooty deposits?

 

Loft installed unit, we have the option of putting it high on the NNW facing flank wall, or up through the pitched roof. 

From this article I was assuming put it on the north wall, but I guess putting it up on the roof would allow I certain amount of "out of sight, out of mind"

 

Any specific vent grill design that would likely reduce the risk? Assuming we keep with wall vent, it will be a white-ish rendered wall, so black spots would show up pretty bad.