MVHR ducting to outside

[Moira Niedzwiecka]

Does anyone have any advice with regard to ducting the MVHR intake & extracts through a TF with 300mm cellulose?

What did you do with the external membrane?

My ducting will go through the wall into a small void in the roof overhang & then a bend in the duct to attach to external grills in the cedar cladding cloaking the underside of the overhang..

Internal wall is airtight OSB (the green stuff).

Thanks. M

 

 

[joe90]

Jeremy,s blog on this is very comprehensive.

[jack]

One thing you might find handy is suitably sized grommets: https://www.greenbuildingstore.co.uk/products/pro-clima-roflex-pipe-grommet/

 

Much neater than strips of airtightness tape, and less likely to fail over time imo.

[dogman]

Just check you do not need a fire collar. As the skin on ours is brick the BC asked for them

 

 

Edited March 5, 2018 by dogman

[Moira Niedzwiecka]

@jack & @dogman Good tips, thank you both.

@dogman Where did you get your fire collars from? Ours has an ironstone skin, but that is below the cedar cladding.

Where the ducts exit the TF is in a roof overhang void.

@joe90 Thanks I'll read Jeremy's blog.

[Jeremy Harris]

15 hours ago, Moira Niedzwiecka said:

@jack & @dogman Good tips, thank you both.

@dogman Where did you get your fire collars from? Ours has an ironstone skin, but that is below the cedar cladding.

Where the ducts exit the TF is in a roof overhang void.

@joe90 Thanks I'll read Jeremy's blog.

 

This is probably the most relevant entry about getting the big ducts out through the walls: http://www.mayfly.eu/2014/04/part-thirty-mvhr-details/

 

With hindsight (wonderful thing..............) I'd have fitted the ducts BEFORE the insulation was pumped in, but I wasn't sure where they were going to have to go.

[IanR]

I went with the Roflex grommets that Jack linked to, plus some Airtightness tape:

 

 

This image is from the outside, and my airtight layer is the outside sheathing board. The membrane then just overlaid this with a hole in in for the duct.

 

You'd need to fix the grommet to the inside.

 

[Moira Niedzwiecka]

19 minutes ago, JSHarris said:

I'd have fitted the ducts BEFORE the insulation was pumped in, but I wasn't sure where they were going to have to go

Same here Jeremy.

I am still not completely decided on what MVHR & where it will go.

I am thinking of going with the Xpelair Natural 180 supplied by BPC.

I will need an installer as I am not able to take this on myself but I am concerned that the ducting is done correctly.

[Moira Niedzwiecka]

3 minutes ago, IanR said:

You'd need to fix the grommet to the inside.

Whats a grommet???

[IanR]

1 minute ago, Moira Niedzwiecka said:

Whats a grommet???

 

Follow the link from Jack:

 

https://www.greenbuildingstore.co.uk/products/pro-clima-roflex-pipe-grommet/

 

Just a flat, square piece of 1mm or 2mm thick rubber with an appropriately sized hole in the middle.

[Moira Niedzwiecka]

Of course. Sorry for being an idiot.

I had just clicked on Jack's link without properly taking in his post.

Thought I was going to have to get a cheese eating dog for a minute.

[dogman]

22 hours ago, Moira Niedzwiecka said:

Where did you get your fire collars from?

see link

https://www.ebay.co.uk/itm/Intumescent-Pipe-Collars-4-Hour-Fire-Stopping-Protection-Sizes-45mm-to-500mm/251893776743?hash=item3aa60a0167:m:mG9-F1b-rbVup7RsIOSPRKg

 

check if your BC officer wants them and if you need 2 hour or 4 hour

[James H]

I am  sorry I don't see why there has to be a fire collar around a pipe that is going out side. These are to stop the spread of fire from one zone internal to another. It needs to be sealed for the air test. That can be done with expanding foam  (fire rated if you want).

This is my in/out for the MVHR. 

The plastic pipe would melt prity quickly anyway. 

Maybe I am wrong but these are my thoughts. 

[Gone West]

5 hours ago, James H said:

This is my in/out for the MVHR. 

It's normally recommended that there is a minimum 3m space between MVHR inlet and outlet.

[Nickfromwales]

1 hour ago, PeterStarck said:

It's normally recommended that there is a minimum 3m space between MVHR inlet and outlet.

Yup, a min of 1500mm is what ive read, but best practice 2000mm or more. 

@James H, can you rotate the grilles so they are at 45o to each other rather than both grilles 'aimed down' ? They are a bit close. What did the manufacturers literature state?

[Jeremy Harris]

7 hours ago, James H said:

I am  sorry I don't see why there has to be a fire collar around a pipe that is going out side. These are to stop the spread of fire from one zone internal to another. It needs to be sealed for the air test. That can be done with expanding foam  (fire rated if you want).

This is my in/out for the MVHR. 

The plastic pipe would melt prity quickly anyway. 

Maybe I am wrong but these are my thoughts. 

 

These are really a fair bit too close together, IMHO, especially in what looks to be a sheltered location.  I think I'd definitely want  to shift one a fair bit further away if it were me.  Ours are around 2.5m apart, and I'm in the process of adding an extension to the intake to increase the separation distance even more.

 

Also, if fitting one above the other, then there can be an even greater risk of cross flow from intake to exhaust.  The exhaust air will usually be warmer than the intake air, as not all the heat is extracted by a conventional MVHR, so that air will tend to rise, so the intake always needs to be below the exhaust if mounting them to the lower limit in the regs, as well.

[IanR]

...and is that a SVP I see just a little further down the wall.

[PeterW]

14 minutes ago, JSHarris said:

These are really a fair bit too close together, IMHO, especially in what looks to be a sheltered location.  I think I'd definitely want  to shift one a fair bit further away if it were me.  Ours are around 2.5m apart, and I'm in the process of adding an extension to the intake to increase the separation distance even more.

 

Thats my struggle too, so I plan to put the intake on the north wall around 2m from the corner, and the exhaust on the east wall about 500mm from the corner - not ideal but otherwise I end up with two around 1400mm apart.

[Jeremy Harris]

2 minutes ago, PeterW said:

 

Thats my struggle too, so I plan to put the intake on the north wall around 2m from the corner, and the exhaust on the east wall about 500mm from the corner - not ideal but otherwise I end up with two around 1400mm apart.

 

 

This is what I did, I put the intake on the North wall and the exhaust on the East wall.  I'm now in the process of moving the intake to the East wall, as the imbalance caused by any slight breeze is audible at the MVHR unit, as it forces the fans to speed up/slow down.  My only option for a fix is to run some external ducting down and across the North wall, to position the intake facing East by a lot lower (probably around 3m away) from the exhaust.

 

There is a secondary advantage to doing this, in that by lowering the intake I can fit an easily accessible pre-filter box, that I hope will reduce the amount of crud that ends up at the intake filter.  I have some left over larch cladding, so intend to hide the extra external ducting in a larch box.  It's at the back of the house, in the alley between the house and the tall retaining wall behind, so won;t be visible from any normal external view.

[Moira Niedzwiecka]

Thats interesting Jeremy.

I had planned to put the intake grill on the north elevation venting downwards from the underside of the soffit overhang & the exhaust on the west elevation on the triangle of cedar cladding.

The vents would be about 2.5m apart.

Would it better to have them both on the north under the soffit overhang?

I could still have them about 2.5m apart.

What is the max distance the intake & exhaust should be from the MVHR?

[le-cerveau]

10 hours ago, Moira Niedzwiecka said:

Would it better to have them both on the north under the soffit overhang?

Yes, from Jeremy's experience, all my intakes and exhaust are on the same elevation, roof vents.

10 hours ago, Moira Niedzwiecka said:

What is the max distance the intake & exhaust should be from the MVHR?

I don't believe there is a max, but the recommendations is to keep it as short as practicable, the longer the greater the pressure increase (resistance) so the harder the fans have to work to do the same job.

[Nickfromwales]

54 minutes ago, le-cerveau said:

Yes, from Jeremy's experience, all my intakes and exhaust are on the same elevation, roof vents.

Do you have a pic by any chance? 

Did you use vertical or horizontal terminals?  

[le-cerveau]

15 minutes ago, Nickfromwales said:

Do you have a pic by any chance?

Here it is, yes there is a section of guttering missing, awaiting arrival of final bit.

The two on the right are exhaust and the 2 on the left inlet, nearly 4m apart. They are UBBINK UB16, Universal Tile Vents, supplied by CVC with a 180mm adaptor to go direct into my 180mm EPS ducting.  This is the NE face of the roof, so less useful for Solar and sheltered from the prevailing SW.

[Nickfromwales]

Very neat solution. I thought they'd be less  inconspicuous TBH. I prefer that to terminals in a gable. 

I assume inline filters? Eg no need to get on the roof ever?

[Gone West]

When I was researching into how to install MVHR around eight or nine years ago I made a list of rules I found relating to connecting the unit to the outside. I'm sure these are not exhaustive and nor are they prescriptive, but it's what I used to install mine.

1. The inlet and outlet grilles should be 3m apart to prevent cross contamination of air. 3m was the distance I found mentioned most often.

2. The inlet and outlet grilles should be high enough (2m) to prevent interference by animals or children.

3. The inlet and outlet grilles should be on the same wall so they are affected equally by the wind.

4. The free flow area of the grill including insect screen should be at least as great as the cross sectional area of the duct.

5. The duct should be smooth wall to reduce air flow restriction.

6. Any ducting bends should be large radius of curvature or two 45 degree bends to reduce air flow restriction.

7. The ducting should slope downwards slightly to ensure any moisture drains to the outside.