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.

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

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

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.

cheapest one stop shop for parts?

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

(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..

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"....

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.

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

<blockquote><cite>Posted By: cjard</cite>How do you reach a situation where scaffolding can be used but ladders cannot?</blockquote>

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

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.

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

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?