Green Building Forum - Basic MVHR schematic and materials Required Plan? Lossnay

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Tue, 20 Oct 2015 11:26:35 +0100

Morning

I acquired a Mitsubishi Lossnay unit which I intend to utilise in my terraced house. This was more of an afterthought so full ducting isn't possible.

In simple terms, will the following be okay:

Extract
One from kitchen (ground floor)
One from bathroom (first floor)

Input
One in attic conversion entrance way (third floor)

I guess there will be plenty of air movement and diffusion so all rooms will benefit and anything is better than nothing.

If this sounds plausible it leads me onto the next part....

Materials required....

A - 3 vents (2 for extract, one for input). What size diameter should these be? The more discrete the better? Link to supplier? Do they need some form of balancing? Aim is to run them both at the same time
B - Ducting? Size from each vent to the lossnay unit?
C - Rectangular ducting - I'll need rigid ducting ideally rectangular from the kitchen through to the unit, something I can wallpaper over or box in, what size and supplier?

Supply Wire....

I have a feed for an extractor fan in the bathroom already wired ready to go, will this be sufficent for the Lossnay unit?

Positioning...

I assume the Lossnay unit will suffice in an uheated attic and just throw mineral wool over it, can I exhaust and supply it from a roof tile vent or even a disused chimney??

Thanks

Basic MVHR schematic and materials Required Plan? Lossnay

tony — Tue, 20 Oct 2015 13:04:51 +0100

A 125mm, B 150 main ducts to outside 125 minimum rigid, C larger rectangular kitchen extract 150 X 65 or similar,

I would plug unit in to a socket

Might need a condensate drain on it, mount on eps platform.

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Tue, 20 Oct 2015 13:43:01 +0100

Okay, do the centres need to be balanced type or any cent will do?

Basic MVHR schematic and materials Required Plan? Lossnay

djh — Tue, 20 Oct 2015 13:49:43 +0100

Caveat: I don't know anything about the Lossnay unit. Look at its installation manual to discover its rating - the fans should take next to nothing and a frost preheater might take current up to a few amps. Any more serious heater will need more serious wiring! As Tony says, just plug it in.

Positioning - don't forget you will need easy access to change the filters - again, consult the manual for details. MVHR is better inside the thermal envelope but it can go outside. Make sure you have some mounting to minimise noise transmission.

Ducts - the manual should tell you acceptable sizes. It's all about keeping the air speed in the ducts down to a level where it's not noisy, which in turn depends on the flow rates of the unit. You'll probably want the same area of supply ducts and terminals as extracts. You'll also want one or two attenuators. As you say, anything is better than nothing but putting supply vents in living rooms and/or bedrooms will be better than the hall if possible. And yes, you'll need to balance it so you'll need some adjustable valves of some kind.

Part F has tables and things on how it is supposed to be done along with the Domestic Ventilation Compliance Guide. Both worth reading. There are other things like this as well:

http://www.encraft.co.uk/wp-content/uploads/2012/08/Viewpoint-August-2012-MVHR-Designing-and-implementing-a-robust-and-effective-ventilation-system3.pdf

Basic MVHR schematic and materials Required Plan? Lossnay

cjard — Tue, 20 Oct 2015 23:09:38 +0100

Seem to recall that the lossnay units don't need a condensate drain because they don't collect condensate?

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12026

Basic MVHR schematic and materials Required Plan? Lossnay

cjard — Tue, 20 Oct 2015 23:12:46 +0100

ps, you cannot draw from an unused chimney unless youre going to put the exhaust in another unused chimney (more than a metre away from the first pot)

mvhr really need the same air pressure on both their world streams, if you fit one to the roof and one to the side of the house you can establish an imbalance in the streams (in the same way a chimney draws air to make a fire go) when the wind blows

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Wed, 21 Oct 2015 12:02:06 +0100

So could I therefore use roof vents 1 metre apart?

The issue I have is the walls are stone and clad in 90mm eps. Hard to drill through high level

Basic MVHR schematic and materials Required Plan? Lossnay

willie.macleod — Wed, 21 Oct 2015 12:54:41 +0100

Don't use this unit with a vertical supply/exhaust setup, recipe for disaster. Put them through the wall. You will get condensate in the vertical external pipes condensing and dropping back ruining the core. Follow the manufacturers instructions to the letter.

This unit comes with 8" ducts. Anything else you will need to drop down with adapters. I compromised with coring 6" holes in my walls.

Installing in a cold loft will require extensive insulation of the ductwork and unit. These are huge units, will not go through a standard loft hatch.

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Wed, 21 Oct 2015 16:49:52 +0100

Okay, I'll see if the walls can be drilled without causing too much mess. What vent covers sould be best for the walls to prevent water ingress?

I guess so long as the unit is above the external vents, all is good.

I will be able to install the unit in the envelope, but the vent hose wont be... that will be fine surely?

And just throw mineral wool over the ducts from the extracts to the unit ?

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Wed, 21 Oct 2015 16:52:26 +0100

cheapest one stop shop for parts?

Basic MVHR schematic and materials Required Plan? Lossnay

willie.macleod — Wed, 21 Oct 2015 21:03:54 +0100

Not sure how you are planning on mounting the unit - the supply air and exhaust air pipes from outside to the unit should ideally run downhill from the unit and not be too long. If you can do that then all should be good. I used bull nose stainless vent covers for outside. Don't do what I did and buy cheap ebay ones, turns out the stainless isn't great at all.... rusty already. BPC in Northern Ireland have very good prices on semi rigid ducting & accessories and have fair shipping costs - if you are planning on expanding your system at a later date I'd use a 75mm semi rigid system manifold and add circuits as and when necessary. Otherwise look for your nearest Lindab supplier.

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Thu, 22 Oct 2015 23:23:03 +0100

What if I used roof vents that were lower than the unit? As my house has an annexe type roof

Basic MVHR schematic and materials Required Plan? Lossnay

Gotanewlife — Thu, 22 Oct 2015 23:30:20 +0100

You'll make a 'U' bend like that and hence will have to allow for drainage at the bottom of the U - we're not talking lots here but with nowhere to go.....

Of course you could get lucky and any condensate might evaporate away....

Basic MVHR schematic and materials Required Plan? Lossnay

cjard — Mon, 26 Oct 2015 18:08:35 +0000

(in lay terms) surely it's condensate because the air was oversaturated with moisture and some of it "fell out", so not quite sure how more inbound air that is also oversaturated will carry away any condensation..

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Mon, 26 Oct 2015 18:13:17 +0000

So you think the roof vent is a no go even if lower?

Any reason I couldn't use the input air from within the attic space? At least it will be pre heated of sorts? And the exhaust vent to a wall vent?

Basic MVHR schematic and materials Required Plan? Lossnay

Gotanewlife — Mon, 26 Oct 2015 22:29:17 +0000

Posted By: VictorianecoAny reason I couldn't use the input air from within the attic space? At least it will be pre heated of sorts? And the exhaust vent to a wall vent?

Not an expert but provided the attic space is well ventilated (in that it will not adversely increase pressure in the system) then I can't see why not. Strictly speaking though, the input and output should face the same way to avoid differential pressure from wind - and you can imagine how strong that might be if you think about what happens if the front and back doors are left open and there is a gust be quiet.

In short: all the MVHR advice, best practice documentation and installation instructions I have read say cold air input and exhaust pipes should slope down way from the MVHR unit and be on the same wall/subject to the same wind pressure - you either have the accept this and make it work or reject it and have a sub-optimal installation. No-one is going to say "Yes you can ignore one of these points"....

Basic MVHR schematic and materials Required Plan? Lossnay

willie.macleod — Mon, 26 Oct 2015 23:12:43 +0000

I can't agree. This unit everyone wasn't designed specifically for domestic use and to use it successfully in your house you are going to have to follow the manufacturers instructions to the letter. It needs lots of clean, fresh air - balanced with the exhaust so don't think about taking dirty air from your loft and increasing the ventilation there, it isn't a good idea for many different reasons. Your fans in the unit are going to have to work much harder shifting air in the loft, the air isn't clean, there won't be anything like enough air flowing there and if there is then you are increasing the heat loss through the ceiling insulation which is always pretty ropey after the first year or two anyway regardless of how deep you fit. It will never balance so you will never get flow rates right. Core two holes out your walls and be done with it.

Basic MVHR schematic and materials Required Plan? Lossnay

djh — Tue, 27 Oct 2015 09:41:54 +0000

Posted By: cjard(in lay terms) surely it's condensate because the air was oversaturated with moisture and some of it "fell out", so not quite sure how more inbound air that is also oversaturated will carry away any condensation..

It wouldn't but the idea would be that it sat there until conditions changed such that the air wasn't saturated. Which is how everything outside dries after it rains. But it's not an ideal situation - almost guaranteed to grow something over time - so best not to design it in. So best to follow Willie's advice IMHO.

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Tue, 27 Oct 2015 21:46:25 +0000

Okay, core drilling from inside to out will be easy but getting a vent will be difficult to do without scaffolding site to no access by ladders.

Easiest way to fit a vent of sorts from inside out?

Basic MVHR schematic and materials Required Plan? Lossnay

cjard — Sun, 01 Nov 2015 12:18:36 +0000

How do you reach a situation where scaffolding can be used but ladders cannot?

Basic MVHR schematic and materials Required Plan? Lossnay

Gotanewlife — Sun, 01 Nov 2015 16:30:30 +0000

Posted By: VictorianecoEasiest way to fit a vent of sorts from inside out?

Not easy but I managed! String, pre-siliconed vent of the type with spring fitting that goes inside the pipe - long bit of wood. Of course I planned it so I had a stub pipe out to outside that was short enough to reach through.

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Sun, 01 Nov 2015 20:51:54 +0000

Posted By: cjardHow do you reach a situation where scaffolding can be used but ladders cannot?

It's above a pitched roof, two storeys up.... A ladder won't go on the roof and would be too steep...

Basic MVHR schematic and materials Required Plan? Lossnay

wookey — Sat, 21 Nov 2015 02:03:35 +0000

Bit of rope access from the chimney? (Being a potholer I think that's perfectly sensible. H&S types would no doubt tut). Not so good if you don't have a chimney or something else vaguely solid to hang off (or the abseiling/prusicking kit).

Basic MVHR schematic and materials Required Plan? Lossnay

wookey — Sat, 21 Nov 2015 02:36:48 +0000

For the external terminals why would I chose stainless cowls vs (cheaper and more discreet) plain louvred vents? Is it mostly about not having the wind blowing straight up the pipe too badly? Not entirely sure I like the look of those cowls (shortest runs have them coming out the front wall of the house so 'not too ugly' is in order)

http://www.bpc-direct.com/cgi-bin/olscgi?cgi_req=102|66 shows both.

Basic MVHR schematic and materials Required Plan? Lossnay

willie.macleod — Sat, 21 Nov 2015 06:09:16 +0000

Posted By: Victorianeco
It's above a pitched roof, two storeys up.... A ladder won't go on the roof and would be too steep...

Cherry picker is the fast and easy way. Find someone local with one, electricians sometimes have one.

Basic MVHR schematic and materials Required Plan? Lossnay

djh — Sun, 22 Nov 2015 16:45:28 +0000

Posted By: wookeyFor the external terminals why would I chose stainless cowls vs (cheaper and more discreet) plain louvred vents? Is it mostly about not having the wind blowing straight up the pipe too badly? Not entirely sure I like the look of those cowls (shortest runs have them coming out the front wall of the house so 'not too ugly' is in order)

I'm a fashion victim so I've got stainless cowls. I think it's as much about keeping the rain out of the ducts as it is the wind. They're supposed to be held in place by two screws into the little holes that you can see in the photo. In my case, it's insulated foam duct behind they're so the screws are bu**er all use and they're siliconed on or whatever was in the nearest tube to hand at the time. But they're still there and looking fashionable

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Mon, 14 Nov 2016 10:07:40 +0000

I spoke to mitsubishi today and they recommend:

1. Not to use slate vents, he did you can but not ideal
2. He also said not to connect to a wet area such as a bathroom....

So that kind of rules out my idea.

Unless anyone has installed one using roof vents and also ducted from a shower room?

Basic MVHR schematic and materials Required Plan? Lossnay

Victorianeco — Thu, 16 Nov 2017 22:07:15 +0000

The arrival of my youngest baby put this project on hold. I have now been up in the attic and there's no way I'm gonna be able to core drill through the wall.

Being a mid terrace there's no other place to route the pipework unless I go roof vents or vent into a bedroom below and out the wall that way which I think would be too invasive.

So, should I scrap the lossnay and get something else? Or just vent to roof slates but ensure the runs are lower than the unit?