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  1.  
    Having installed the MVHR intake and exhaust ducts in insulated duct, I am now wondering if there is any advantage to having one route shorter or longer than the other? I used existing holes through the 450mm thick stone walls, they are more than 1.5m apart along the wall on the outside. As you can see, one route is longer and goes down and back up again to get around the joists (then falls to the outside through the wall). The other one falls continuously to outside.

    I can arrange it at the unit end so that either of them is intake or exhaust, although one arrangement will be slightly neater than the other.

    Does the hive mind have any thoughts or insights?
    Or am I over thinking it and should just go for the neater arrangement?
    My instinct says exhaust on the right with the shortest route and the constant fall, but the opposite is the slightly neater layout in the utility room.
  2.  
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      3442BC8A-8021-404B-B2D2-D14EBF03F6BB.jpeg
    •  
      CommentAuthordjh
    • CommentTimeMay 16th 2020
     
    Yes, exhaust with the continuous downfall - the air in it will be closest to saturation. Just my 2p.

    How will you prevent water getting into the other duct, and how will you drain any that does from the lowered section of duct?

    Is this area within the heated envelope? I'm thinking about all the other ducts.
    • CommentAuthorEd Davies
    • CommentTimeMay 16th 2020
     
    Posted By: Dominic CooneyMy instinct says exhaust on the right with … the constant fall


    That'd be my instinct, too. The exhaust air should often have some water droplets in it which you want trickling outside rather than settling in that U of rectangular duct.

    OTOH, that U could be a trap for all sorts of horrors, whether it's used for inlet or exhaust, so maybe you'd want it on the exhaust side so at least you're blowing them outside. Does it have a slope to it - hard to see from the picture but maybe it slopes down to the left - so perhaps it could usefully have a drain at the low point.

    Part of my design is that it'll be all downhill from the exchanger to the external vents on both the inlet and exhaust sides.
  3.  
    Posted By: djhIs this area within the heated envelope? I'm thinking about all the other ducts.


    Yes the other ducts are within the heated envelope. As I understand it the intake and exhaust should be insulated all the way.



    Posted By: djhHow will you prevent water getting into the other duct


    It slopes downwards as it goes through the wall from inside to outside, so 500mm of pipe sloping downhill to outside with an aluminium louvre/grill on the external wall (fitted with insect mesh). I can't see rain getting uphill that far?

    Because the distance is relatively short I could feed an endoscope in from outside to check for water, and even feed a hosepipe in to syphon it out! I'm hoping that because the total length is only about 3m from outside air to the unit that this will be shorter than many other installations and that being constantly ventilated will keep it dry?

    Posted By: Ed DaviesPart of my design is that it'll be all downhill from the exchanger to the external vents on both the inlet and exhaust sides.


    Would have been preferable but not easy to make work in my situation (use existing holes through wall and keep them >1.5m apart)

    I will go with the exhaust on the right. Thanks for your thoughts.
    •  
      CommentAuthordjh
    • CommentTimeMay 16th 2020
     
    Posted By: Dominic CooneyAs I understand it the intake and exhaust should be insulated all the way.

    Yes, that's right. It was just whether the other ducts also needed insulating, but it seems not.

    It slopes downwards as it goes through the wall from inside to outside, so 500mm of pipe sloping downhill to outside with an aluminium louvre/grill on the external wall (fitted with insect mesh). I can't see rain getting uphill that far?

    I was just being pessimistic. It depends at least on how steep the fall is, what the design of the external cowl is like and how strong the wind is whether there will be a problem in reality. I'd be inclined to put a small drain on the bottom with a [short] length of clear tube attached before a valve, so you can see if there's any water standing there and drain it if necessary. You can insulate the clear pipe if you wished.

    I expect I'm over-concerned. Expect the unexpected and all that.
  4.  
    Louvres now fitted as well (just come in from doing it). It’s quite sheltered round that side because it’s between 2 buildings, but you never know.
      C1F918F5-8AF8-47CA-9B6F-04AC01A567EB.jpeg
  5.  
    Nice wall !!!
  6.  
    Posted By: Peter_in_HungaryNice wall !!!


    Thanks P_i_H !
    We are currently deliberating how much or little to point it. It’s the only elevation that wasn’t horrifically strap-pointed with cement mortar. All the others have now been redone with lime putty mortar. There are however some big gaps and we are wondering if we can get away with just a bit of sensitive pointing targeted where it needs it most. SWMBO wants to leave it as it is, I would probably veer towards doing the whole lot, because once the cracks and the big gaps are done there’s not a lot left!
    •  
      CommentAuthordjh
    • CommentTimeMay 16th 2020
     
    Posted By: Dominic CooneyWe are currently deliberating how much or little to point it. It’s the only elevation that wasn’t horrifically strap-pointed with cement mortar. All the others have now been redone with lime putty mortar. There are however some big gaps and we are wondering if we can get away with just a bit of sensitive pointing targeted where it needs it most. SWMBO wants to leave it as it is, I would probably veer towards doing the whole lot, because once the cracks and the big gaps are done there’s not a lot left!

    If you can leave it as it is, then that's definitely easiest! There are only one or two gaps that leap out from the photo; if you try to do just those, or even the entire wall, then I'd be tempted to colour the lime a very dark brown or black so the wall doesn't change in appearance much.

    Having said all that it looks like some bits up top are already pointed with a light-coloured mortar?

    +1 on the nice wall comment, BTW.
  7.  
    Posted By: djha light-coloured mortar?


    Eagle eyes djh!

    But actually original mortar up there, it’s almost completely white now, with some big lumps of charcoal in the mix!
    There is some repair on the left where a concrete block wall was unceremoniously toothed in (read smashed in!) to the stonework. It has a reddish pink mortar - quite glad you haven’t spotted it!
      D0337588-1DEA-44AB-8137-290075A085C5.jpeg
    • CommentAuthorGreenPaddy
    • CommentTimeMay 17th 2020
     
    Interested to know what type of insulation you're planning to add to the ducts, to take it up to something closer to the exterior envelope insulation values?
  8.  
    Hi GreenPaddy, do you mean the flexible ducts? They will remain inside the heated envelope.
    Or do you mean that the thermal ducting should have additional insulation? If so, I wasn’t expecting this and there is no room for it....:sad:
    • CommentAuthorGreenPaddy
    • CommentTimeMay 17th 2020
     
    The intake and exhaust ducts carry air at the temp of external air (a degree or two warmer in the case of exhaust).

    Essentially those two ducts are a continuation of your building thermal envelope. So, you should insulate them as you would your walls, roof, floor, etc.

    Will the world stop spinning if you don't do that? No.

    Will you get heat loss at those ducts, that also reduces the effectiveness of the MVHR? Yes.

    Will you get condensation on the surface of the grey insulation? Probably not, though that depends upon the absolute humidity inside the house next to the ducts, and also whether the MVHR reduces intake volumes to prevent exchanger frosting in sub-zero external temps.

    I would at least pack some wool insulation around the duct in the floor void, and anywhere else you can sensibly insulate. I assume you went to the trouble of keeping the flat duct against the wall to minimise visibility, but maybe if you box those in, use some laminate plasterboard?
  9.  
    Yes and good tips thanks, I will pack the floor void with rockwool around the pipes. đź‘Ť
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