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Hi.  I am sure this question has been asked.

The MVHR system works by sucking in cool fresh air and warms it by exchanging the heat with the stale air on the way out.

I presume the intake point cannot differentiate between polluted air and less polluted air. For instance on a cold winters evening if there are fires burning either side of you, how does the intake not pull in smokey dirty air... i realise there is a filter but that can only do so much right..

Probably, a stupid question?

Thanks

M

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Not a silly question at all and it's come up on here before with bonfire smoke bring sucked in.

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Not stupid at all.  There is a neighbour beside me who I swear must burn tyres in his house as the smoke is black.  When the wind is blowing it my way I have to turn the  mhrv of as the smell gets into the house.  The filters will take out the bad particles but can't stop the smell. Luckily it only happens 3-4 times a year. 

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i live in the country so i dont think it would be a problem but i imagine in a city it must be a nightmare

 

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Imagine living with MVHR in one of those countries where they burn confiscated drug crops...or even in the UK if your neighbours are partial to a puff...

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Yep its a problem with mvhr.

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I wrote in a previous post that a friend put me off installing a MVHR For all the above reasons 

But like Dec says you can always switch it off

 

i must admit that the next one I do 

I will install MVHR 

Not a fortune in the grand scheme of things 

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Think @JSHarris did something ref the position of his intake or was going to, to alleviate this issue.

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Think I'd fit a smoke detector in the intake if I ever did it.

 

The scare story I love is about the burst pipe in the passive house. It was so well sealed the owners couldn't open the inward opening doors from the outside and could only look through the windows at their possessions floating about! 😂

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Posted (edited)

Postition of intake cant change air if its full of smoke etc it will still get pulled in mvhr filters pollutants - large or small dependent on your filters - not noxious air..also I had not from external air intake but from trap......my condensate drain kept drying out and I got sewage smells  pumped round the house was awful!

Edited by lizzie

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32 minutes ago, Onoff said:

Think I'd fit a smoke detector in the intake if I ever did it.

 

The scare story I love is about the burst pipe in the passive house. It was so well sealed the owners couldn't open the inward opening doors from the outside and could only look through the windows at their possessions floating about! 😂

LOL. We have two low level shower trays downstairs so, in theory, that couldn't happen, and most will have a loo downstairs so difficult to see water level rising above 15 inches or so indoors.

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2 minutes ago, NSS said:

LOL. We have two low level shower trays downstairs so, in theory, that couldn't happen, and most will have a loo downstairs so difficult to see water level rising above 15 inches or so indoors.

 

That'd be enough to keep the doors shut!

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Just now, Onoff said:

 

That'd be enough to keep the doors shut!

I'll take your word for that as I have no intention of testing the theory 😉

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In the past couple of years we've had maybe three or four occasions when we've had to turn the MVHR off for a couple of hours because of smoke outside, but if we didn't have MVHR then those were days when we'd have had to go around closing windows and vents to keep the smoke out anyway.  At least with MVHR just flicking the switch to turn it off fixes the problem until the smoke clears outside.

 

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@Moggaman, chuck "mvhr bonfire" in the search box (no quotes) and a few interesting threads will pop up. There's chat in "Why Insulate?", "MVHR Intake", "Carbon Filter" etc.

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9 hours ago, Declan52 said:

The filters will take out the bad particles but can't stop the smell.

If you can smell something you must be breathing in molecules of the substance but whether they can be dangerous or not I'm not sure. What do you think @JSHarris.

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7 minutes ago, PeterStarck said:

If you can smell something you must be breathing in molecules of the substance but whether they can be dangerous or not I'm not sure. What do you think @JSHarris.

 

It's really hard to be sure, but if the MVHR intake filter is an F7 (the finer pollen filter) then that should filter down to about 1µ, so will remove the majority of the smoke particulates.  I suspect that the smell is from trace amounts of volatiles, that most probably aren't particularly harmful, especially in a situation where they are only present for a short period of time.  I would guess that these could be reduced using an activated carbon filter, but an activated carbon filter is likely to need more frequent replacement than a normal intake filter.

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We occasionally get the most horrendous smell in the area. Someone said it was "silage"? Really wouldn't want to be dragging that in!

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9 hours ago, NSS said:

LOL. We have two low level shower trays downstairs so, in theory, that couldn't happen, and most will have a loo downstairs so difficult to see water level rising above 15 inches or so indoors.

I was part way through wiring a barn conversion many years ago. One night there was torrential rain, and the mains drainage backed up and sewage poured out over the rim of the downstairs loo and caked the whole ground floor with smelly stuff.

 

There was quite a delay while they lifted all the floors and cleaned it all up. I pitty the owners. 

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1 hour ago, JSHarris said:

but an activated carbon filter is likely to need more frequent replacement than a normal intake filter.

 

I plan to make or modify a filter housing to take one of these

 

At £10 a shot, changing every 3 months won’t be an issue, and they are not a bad size to fit the standard housings. Active carbon plus pollen should be pretty good. 

 

 

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18 minutes ago, ProDave said:

I was part way through wiring a barn conversion many years ago. One night there was torrential rain, and the mains drainage backed up and sewage poured out over the rim of the downstairs loo and caked the whole ground floor with smelly stuff.

 

There was quite a delay while they lifted all the floors and cleaned it all up. I pitty the owners. 

 

Its for precisely this reason that in periods of heavy weather I cling film all the bowls over. 

#paranoia 

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8 minutes ago, Lesgrandepotato said:

 

Its for precisely this reason that in periods of heavy weather I cling film all the bowls over. 

#paranoia 

I suspect that would not hold back sewage under pressure.

 

If that had happened to me, I would be worried it would happen again, and I would be organising an external vent that was lower than the level of the WC rim in the hope next time it would fill the garden instead.

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30 minutes ago, Lesgrandepotato said:

 

Its for precisely this reason that in periods of heavy weather I cling film all the bowls over. 

#paranoia 

 

 

19 minutes ago, ProDave said:

I suspect that would not hold back sewage under pressure.

 

Not a practical joker, then, @ProDave?

 

I remember the "cling film over the loo" trick from uni days, where at least one young lady of our acquaintance ended up with a soggy bottom when peeing into a loo that had had the cling film treatment...

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Yes we are in the country where “liquid muck” is spread over the fields but easy to switch the MVHR off for a while, better than living in a town with all the other invisible pollutants in my opinion !

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34 minutes ago, joe90 said:

Yes we are in the country where “liquid muck” is spread over the fields but easy to switch the MVHR off for a while, better than living in a town with all the other invisible pollutants in my opinion !

 

I get that on and on but there is a farm behind me so not that surprising. Doesn't happen constantly though as it's just a 'country smell' afaic but wouldn't want it in the house! 

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