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MVHR and boiler flue outlets


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Hi we are close to coring out holes for the MVHR inlet/outlet and boiler flue holes. I need to locate these in the plant room and ensure that minimum separation to meet BR is met. The guidance seems somewhat confusing.

 

I have attached a spec sheet of the MVHR unit and the floor plan for reference. The unit is wall hung and the Right hand version.

 

It was our intention to install the MVHR unit on the left hand wall in the room near the corner 300mm from floor level. This gives us an installed height of about 1050mm meaning the lowest point at which we can have an outlet will be about 1400-1500mm from floor level. It is my understanding that the inlet should be at a lower level than the outlet and a minimum separation of 1100mm (centre-to-centre) is required. By positioning the inlet as low as possible and towards the middle of the outside wall and the extract near to the ceiling we should be able to achieve this. 

 

The boiler is floor standing and will go on the outside wall in the right hand corner with the flue running to near ceiling height and out.  Effectively this would give us a triangle with the distances beteen the 3 points being roughly similar at 1100mm or thereabouts

 

Does this make sense and comply or am I missing something fundamental?

 

If this doesnt work, we would have to move the MVHR onto the left hand wall by the entrance door and have ugly ducting crawling all over the walls.

 

Inputs gratefully received.

Adroit-DV145 Spec.pdf

1229.02.02K.pdf

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Would be better to have the MVHR inlet and boiler flue on different walls of the house if possible. Will the boiler flue be up-wind or down-wind of the MVHR inlet?

 

How big is the gas boiler (eg power output)?...

 

http://support.ambirad.co.uk/article.aspx?id=10724

 

Also check the boiler makers installation instructions. Sometimes these over ride the Building Regulations, for example when the boiler maker says you need a bigger separation.

 

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Our 180mm MVHR penetrations are 1.5m apart but are level - I'd not heard of any requirement to have one higher than the other. Ours sit about 300mm from finished external paving level as they rise from the basement and exit behind utility cupboards.

 

Our boiler flue is round the corner so that's not an issue wrt MVHR, however it was a pain to get it in the correct spot, being 300mm (or whatever the regs say) away from the rear utility door and 2100mm above finished paving level. Note it was the GS installer (our plumber) who insisted on those separations, not BC.

 

I have to say, our independent BC guy didn't pay much attention to the MVHR - he asked for a commissioning cert but I explained that it was a DIY install so he's settling for a copy of the unit specs to ensure it's appropriately sized for the dwelling.

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I'd suggest that getting as great a separation from the boiler flue and the MVHR fresh air inlet would be a good thing, irrespective of the regs, and also try and make sure the boiler flue is usually downwind of the MVHR inlet, if possible. 

 

Our old house has the boiler flue above, and about 2m horizontally, from the back door.  This is within the regs, but less than ideal, as we get a definite momentary smell of gas in the kitchen if the back door is open and the boiler fires up.  The back door happens to be almost always downwind from the flue, so the momentary release of unburned gas during ignition is enough to create a small nuisance.  The boiler is working fine, and it's normal for there to be a short duration emission like this as the boiler fires, but I think I'd not want any risk of that getting sucked into the MVHR.

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4 hours ago, Bitpipe said:

Our boiler flue is round the corner so that's not an issue wrt MVHR, however it was a pain to get it in the correct spot, being 300mm (or whatever the regs say) away from the rear utility door and 2100mm above finished paving level. Note it was the GS installer (our plumber) who insisted on those separations, not BC.

Your GS guy was right to strive to get those dimensions, and yes, it's usually 300mm from any adjacent opening in the fabric of the property, regardless of whether it's an inlet or an exhaust. The mvhr may be turned off or break down, so you cannot rely on it being an exhaust as if there is a failure it then becomes an inlet ( as far as the boiler products of combustion are concerned ;) ). 

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6 hours ago, ryder72 said:

The boiler is floor standing and will go on the outside wall in the right hand corner with the flue running to near ceiling height and out.  Effectively this would give us a triangle with the distances beteen the 3 points being roughly similar at 1100mm or thereabouts

What boiler is it? Assuming oil or a WB High-Flow heat store combi if it's a floor stander ?

Make and model please :)

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4 hours ago, Temp said:

Would be better to have the MVHR inlet and boiler flue on different walls of the house if possible. Will the boiler flue be up-wind or down-wind of the MVHR inlet?

 

How big is the gas boiler (eg power output)?...

 

http://support.ambirad.co.uk/article.aspx?id=10724

 

Also check the boiler makers installation instructions. Sometimes these over ride the Building Regulations, for example when the boiler maker says you need a bigger separation.

 

This might sound daft, but wont the upwind/downwind answer depend on the wind direction. For what its worth the inlet will be to the west of the flue. Most likely by about a meter in the horizontal plane and a meter in the vertical plance.

 

Its a condensing oil boiler 15-21kW.

 

The most separation we will manage is 1.5m on a horizontal plane so we have to use a combination of vertical and horizontal planes to ensure we are compliant

19 minutes ago, Nickfromwales said:

What boiler is it? Assuming oil or a WB High-Flow heat store combi if it's a floor stander ?

Make and model please :)

Grant Vortex Eco utility System 15/21 oil condensing boiler.

 

My thinking was that stale air from the MVHR extract and flue gases will be warmer and rise so keeping them above the MVHR inlet minimises the chance of the MVHR unit sucking flue gases or stale air back in.

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35 minutes ago, ryder72 said:

This might sound daft, but wont the upwind/downwind answer depend on the wind direction. For what its worth the inlet will be to the west of the flue. Most likely by about a meter in the horizontal plane and a meter in the vertical plance.

 

 

Yes, it does depend on wind direction, but both our new build and the old house are at the bottom of valleys that run more or less east/west, so the wind is almost always from the west, as a consequence of the prevailing wind direction in the UK and the impact of the local topography on surface wind.

 

35 minutes ago, ryder72 said:

My thinking was that stale air from the MVHR extract and flue gases will be warmer and rise so keeping them above the MVHR inlet minimises the chance of the MVHR unit sucking flue gases or stale air back in.

 

Our experience at the old house is that the flue gases get blown downwards pretty much all the time.  We have our wheelie bins up against the wall beneath the boiler flue, which is around 2.4m above outside ground level, and if we happen to be standing there when the boiler fires we pretty much always get a brief smell from the flue.  A lot will depend on how the air tends to flow around the house, but I'm not sure you can always rely on the flue gases rising, mainly because they aren't that much warmer than the air a lot of the time, especially for the few seconds after the boiler fires, when it's really just the fan that's pushing air through the boiler, that's sucked in from outside..

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1 hour ago, Nickfromwales said:

Your GS guy was right to strive to get those dimensions, and yes, it's usually 300mm from any adjacent opening in the fabric of the property, regardless of whether it's an inlet or an exhaust. The mvhr may be turned off or break down, so you cannot rely on it being an exhaust as if there is a failure it then becomes an inlet ( as far as the boiler products of combustion are concerned ;) ). 

 

FYI - Challenge was getting the placement in the MBC frame construction as there was a structural rib fouling the preferred spot, but we managed to squeeze it in. 

 

Note the 300mm is from the actual door aperture, not the door frame and that's what saved our bacon on this occasion.

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1 hour ago, JSHarris said:

 

Yes, it does depend on wind direction, but both our new build and the old house are at the bottom of valleys that run more or less east/west, so the wind is almost always from the west, as a consequence of the prevailing wind direction in the UK and the impact of the local topography on surface wind.

 

 

Our experience at the old house is that the flue gases get blown downwards pretty much all the time.  We have our wheelie bins up against the wall beneath the boiler flue, which is around 2.4m above outside ground level, and if we happen to be standing there when the boiler fires we pretty much always get a brief smell from the flue.  A lot will depend on how the air tends to flow around the house, but I'm not sure you can always rely on the flue gases rising, mainly because they aren't that much warmer than the air a lot of the time, especially for the few seconds after the boiler fires, when it's really just the fan that's pushing air through the boiler, that's sucked in from outside..

So we are on a slightly exposed location and these outlets are on the the northern elevation which is the least exposed of the 4 elevations. The building is a proper cube so I suspect the airflow will be quite  disrupted around the building. The prevailing wind direction is west  so we will have the flue downwind of the inlet but I suspect when the air gets round the building it will be a very disrupted air flow to get anything meaningful direction on it.

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