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Richardk
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Our VMC provides the outlet in our shower room (rooms a grand word..... it's only a little bigger than the shower itself) for all the steam created by the shower. The problem we have is it's not working effectively enough as we get a mould build-up on the wall near the top of the room. We leave the door to the shower room open all day and when taking showers.

The VMC goes straight up throught the ceiling and into the attic. Then a c. 4m horizontal run, up the wall and then through to where the VMC unit is located. Due to our hot water tank also being in that area at the point the pipe dips in a large 'U' shape - c. 60cm in depth. There is no water gathering in this section of what is flexible pipe.

Originally I'd though I should get rid of the 'U', however, as this doesn't seem to have any liquid build-up I'm not convinced it will solve the problem. Another alternative would be to fix a seperate extractor fan which would vent directly itno our bedroom (it's an on-suite shower).

Does anyone have any ideas/suggestions/views on what course of action I should take?

Richard
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Hi Peter - thanks for your reply ... and for confiming that 'U' shapes are not supposed to be there. Could you explain what an asymetric blanking piece is and where I would find it? Presumably at the VMC unit itself but what does it look like on yours?

Thanks,

Richard
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Hi

Where the pipe joins the VMC, the inlet was shaped like a circle with a large half moon cut out. Between this and the pipe was a similarly shaped spacer which adjusts the airflow by being rotated in its mounting.

Hard to describe, but simple when you see it !

Peter

 

 

 

 

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Hi Di - our own unit is perfectly accessible hence no need to go to the Brico thanks. I have to admit to not having looked yet but from memory I don't remember seeing the sort of discs Peter has on ours. I suspect I'll try and find a manufacturer name on the unit and do some research on the internet for how to regulate as I imagine they are all adjustable in flow/draw to a degree.

Richard
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  • 3 weeks later...

Apologies for a slight side track but, what is the

difference between a VMC and an extractor fan inline in the ducting (apart from

the fact that a VMC allows for several inlets. 

Is a VMC more powerful ?

I have an extractor (inline in the ducting rather than a

traditional extractor) and am wondering if I should get one of these VMC

thingy’s.  Currently only a bathroom but

hopefully in future a 2nd bathroom.

Also, how is the extraction controlled (i.e what activates

and de-activated a VMC) ?

 

Many thanks

Ian

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There are either manual or automatic VMCs. The cheaper manual ones (40-50 Euros) come with just a speed control switch. The general idea is that they are controlled by a light or a seperate on/off switch somewhere. They shouldn't be running 24/7, but often are where there has been a damp problem.

The other type, which are about 15-20 Euros dearer have a Hygrostat in them that detects moisture. The VMC thus switches on and off according to the level of moisture in the air at ANY of the inlet ports. These usually come with speed switch too, which allows variation in extraction power.

All VMCs have some means of controlling the level of extraction in each port. This can be as simple as a thin flexible baffle.

VMCs are designed to avoid having to pierce thick stone walls. The normal exhaust port is through a roof plate, or through the eaves. If the eaves method is used, avoid birds and other unwanted guests entering the VMC by adding a grille to the pipe outlet.

 

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Hi, our plumber, when told I was going to fit a vmc, told me to use rigid pvc pipework in the visble areas, (we have visible beams etc, and the bathroom, (not finished yet) is downstairs at the moment, so through the floor into a bedroom is not an option).

Is this OK? Are connectors etc for rigid/flexible available?

Alcazar

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[quote user="Opel Fruit"]

There are either manual or automatic VMCs. The cheaper manual ones (40-50 Euros) come with just a speed control switch. The general idea is that they are controlled by a light or a seperate on/off switch somewhere. They shouldn't be running 24/7, but often are where there has been a damp problem.

The other type, which are about 15-20 Euros dearer have a Hygrostat in them that detects moisture. The VMC thus switches on and off according to the level of moisture in the air at ANY of the inlet ports. These usually come with speed switch too, which allows variation in extraction power.

[/quote]

Opel Fruit, I am curious about this.  I am sure what we have is the cheaper kind and I can distinctly remember that the instructions said that it must be hard wired with no means of turning it off.  There is only the speed control switch.  I thought that was the point of the VMC, it works all the time with a boost if, for example, you want to clear the bathroom after a shower.  In fact we put ours through a time switch so that it is not on all night and were conscious that it probably contavened the regs.  Have they changed the regs?

Liz (29)

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Firstly, I am not an expert on VMC, by any means. But for what it's worth:

VMCs or VMIs can be used full time, though I have never seen instructions saying that they can only be hardwired to the tableau. Typical instructions I have on CD state that the switch (run/marche) can be placed wherever convenient. I would suggest that since these units can shift "hundreds" of m3 of air an hour, an awul lot of (expensive) heat is going to be drawn out of the building.

The advantage of Hygrostat control is clear.

Most new builds have VMC double, which incorporates heat recovery for this very reason. 

I think in the final analysis, the owner must judge whether any extraction system needs to be on all the time, but cannot think of an obvious or economic reason why this should be so. I personally think they are excellent, and would thus use them in accord with the needs of the application.

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I wouldn't dream of switching mine off. If turned on and off they build up with humidity and we have seen the consequences when people have done that.

A well insulated home should be an envelope with those tiny trickle vents in some of the windows, not all, and this way, using a VMC a home is well ventilated without drafts and as far as I am concerned sans great heat loss either. We only have the VMC ducts into rooms without trickle vents,  ie the bathroom, kitchen and toilet. It all works perfectly well.

And yes we can turn it up or off if we so wish. As it is we simply let it do it's job.

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The “going continuously” does sound like a good way to empty

the house of warm air.  If the room is well

insulated (no drafts), then seems to me the VMC will not be extracting anything

(only using electricity).  If the room

is “leaky” then it will move warm air from the house to the outside.

 

In my case, the “activation” is a bit of a concern as the

house has a 3 phase supply and to “balance” the phases, all 3 phases are used

through the house.  This, it would be

difficult to ensure that the VMC (serving different rooms) was on the same “phase”

as any activation (e.g. light switch in the room).  I do not know (and would not be confidant enough reading the

instructions) what would happen if the VMC power and activation were on

different phases (i.e. 400V across them !!).

 

Maybe I’ll stick with extractor fans inline in the ducting

(as I will only be needing two).

 

Ian

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We had VMC put into our house in 1983 when we moved in. The first unit was very expensive and we replaced it a few years ago and bought one for about £60. We have a warm cosy house and it does not feel like we are having all the warm air sucked out at all. Others have this system and I am pretty sure that they leave it running all the time too. Quite simply, it is good.

Our neighbours used to switch on and off and the humidity got left in the VMC and it broke down. Also as their house was as well insulated as ours they started getting problems with damp too. We haven't. I love these and would have them anywhere and use them. As a good yorkshire woman I don't like wasting money and don't believe I am.

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I agree with TU, we've never switched ours off and we have never noticed heat loss (or gigantic leccy bills). The only time I'm concious of any noise is if I'm working up on the mezzanine (without the radio) as the VMC unit is in the eves above and I can hear a very low whirring sound.

However, ours doesn't go to the downstairs bathroom as it wasn't possible with the pointed walls - in there a normal extractor fan which is wired to the light switch. That was installed above the bath/shower - big mistake as it's freezing in the winter when lying in the bath with a down draft, so I just have the mirror unit lights on!

Anyway, although I had no idea what one was when our French electrician insisted on installing it, I wouldn't be without the VMC now, in any house. In the kitchen/living room it is unnoticable but gets rid of stale cooking and smoking smells WITHOUT making the room cold in any way. I just wish that they are installed as standard in the UK as my Mother nearly died (cats died) through carbon monoxide poisoning caused by a faulty multi fuel boiler. That will never happen to us here.
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