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So now we have an electric connection (7 days and counting) I've started to run the MVHR unit 24x7 but since then we've started to notice little flies in one room.  Having pulled off the MVHR supply air vent in this room it contains many of the little beggars trapped in the foam as per photo.

 

Two weeks back I vacuum cleaned the MVHR filters, apart from being a bit dirty with 12 months of limited use there were no flies, today the exterior filter contains a few of the same flies (which I might expect as it does its work) and the house side filter seems ok.  

 

FYI our new build is called Field Cottage, it is in the middle of a field - currently just ploughed after a crop of wheat harvested 6 weeks ago, while there are flies about I would not say there are swarms of these types.

 

Have to admit since the air tightness test was done, also the same day the electric was connected, me and my partner don't feel the MVHR is delivering the same volume of fresh air - maybe the summer by pass has turned off or worse case a pipe has popped somewhere - yet to investigate.

 

Unit is a Vent-axis Sentinel Kinetic plus B.

 

Can the flies get past the filters or do I have my partners worse night mare, a fly infestation in the MVHR pipework? (She told me this many times over the long build and we pretty much kept all the pipe work sealed and ditto the MVHR).

 

IMG_20170927_200154.jpg

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I wonder how they are getting past the main intake filter?  I changed our filters and cleaned the housings out a couple of weeks ago, and as usual the intake filter box had a fair few cobwebs, dead flies etc in.  Given that this filter can filter out pollen, I can't see how those harvest flies could get through.

 

As @jack suggests, this indicates that there are gaps around your main intake filter somewhere, and that the harvest flies are getting past it and being drawn in by the fan.  They will easily get sucked in by even a low suction, as they are not powerful fliers.  I managed to fill our bedroom with them when I was positive pressure air testing our old house; my home made fan sucked hundreds of them in, covering the walls etc with little black specs.  It took me ages to clean them all up before SWMBO came home.................

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In theory, this shouldn't be a long term problem. Most likely, the flies that are in the ducts will be pushed out by the moving air (they're probably already all out). Unless they're actually getting by the filter, that should be the end of it.

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Could they have got in before the house was sealed and gone their to die?

 

We have a peculiar thing here that ordinary "house flies" at the end of the season will crawl into the gap between the opening windows and frames * and go there to die.  Should you open a window, it will unleash many tens of half dead flies many of whom fall into the house.

 

* This is not a defect in the windows. The outer seal is a rain seal, and is open at the bottom to let any water that gets passed out. That is where the flies crawl in. The inner seal that makes the air tight seal between the window and the frame is not breached by the flies

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5 minutes ago, ProDave said:

We have a peculiar thing here that ordinary "house flies" at the end of the season will crawl into the gap between the opening windows and frames * and go there to die.  Should you open a window, it will unleash many tens of half dead flies many of whom fall into the house.

 

 

We have that,  but they are not ordinary house flies, they are "cluster flies" round our way. Normal fly spray does not kill them, you have to get them with other stuff (standard Ebay issue). The thing with cluster flies is that they are actually pretty harmless AIUI, they don't lay eggs in food and so forth.

Edited by gravelld
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We had a big problem with cluster flies in our first house in Scotland.  It was right next to farmland, by the shore of Loch Ryan, and the window frames would be full of the things if you opened a window.  They would crawl in though the narrow outside gap and gather in large numbers in the small sheltered space outside the inner seal.  I found that the paint-on stuff worked well.  Not sure of the name of it, but you just open the windows and paint on a thin layer of the stuff around the hidden areas.  It seemed to last for around a year, and either killed, or dissuaded, cluster flies from crawling into these spaces.

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  • 7 months later...

2018 Spring we have a different type of fly getting through the MVHR.

 

I've been keeping on top of the filter cleaning but it seems more flies are trapped at the terminal than the filters!

 

Oddly the flies have a preference to come out of the vent with the very shortest run even though that vent is nearly 100% closed (it is in the spare bedroom so I tend to close it down alot when there are no guests)

 

In 2017 I took the air exchanger unit out and cleaned it (as per 12 month maintenance cycle) and there were a few flies in it too, though not enough to worry about.

 

However I did notice then that there are various ways air can pass from the fresh air in to the fresh air out without going through the filters or heat exchanger - mainly via the poorly sealing front cover.  I tried to add more foam to prevent this but it seems a long way from being 100% sealed.

 

Any one else with a Vent-Axis Sentinel Kinetic Plus B?  And if so are you seeing poor filtration?

 

 

 

 

IMG_20180518_080255.jpg

WhatsApp Image 2018-05-17 at 22.02.31(1).jpeg

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I live in midge central and my vent axia b+ seems to filter them out pretty good. Are you sure that you have everything fully clicked in place after cleaning it.

Or can you add a finer mesh to your inlet/outlet covers to stop them here.

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We also get flies in the filter chamber of ours, but nothing gets through the pollen filter on the intake side at all.  I took the heat exchanger out of ours last year to see if it needed cleaning, but it was spotless, no trace of any dust or anything in it.  We do have a problem with fluffy floating seeds partially blocking the intake grill outside, which means I have to get up a ladder with a brush and clean it periodically, but I'm planning on running an external duct extension from that down to a lower level, with an easily accessible pre-filter screen, as a long term measure to try and help keep the main filter a bit cleaner.

 

I agree with what @Declan52 has said, it sounds like the filter isn't sealing properly and is allowing stuff to bypass it, so it's worth checking that everything is properly fitted and sealed.

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I have one - have not had this issue but agree that the seal between incoming filter and chamber is not 100% - I gave our heat exchanger a good clean last year once we'd finished our landscaping - was quite grubby but scrubbed up well.

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  • 3 months later...
On 28/09/2017 at 07:35, JSHarris said:

I wonder how they are getting past the main intake filter? 

 

Main intake filter?  I have external cowls with grills which are connected direct to the MVHR unit.  The MVHR unit has built in filters but VentAxis are saying my problem is there are no external filters.  Is it usual to have external extra filters (i.e. some sort of filter box for the incoming air before it reaches the MVHR unit?) 

 

My system was designed by a well known supplier of ventilation units and an external filter was never mentioned.

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No external filter on ours, and we rarely get anything in the internal filters that an external filter would have stopped. However, our inlet is on the flat roof over our garage, so possibly a little out of the way for casual insects 

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No external filters on ours, either, although there will be one on the intake once we've got the old house sale out of the way and I have some "tinker time" available again.  The plan is to relocate the external intake a bit lower down, so it's more readily accessible, and fit a fairly coarse, washable foam filter, so it's easy to change/clean.  I'm hoping that will extend the life of the fairly expensive pollen filter on the intake side of the MVHR unit itself.

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