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Heating and cooling: MVHR on a shoe string?

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  1.  
    Evening folks,

    I've decided to put in a mvhr system in my 4 bed mid terrace which is probably not very airtight.

    I did intend to throw in 2 budget extractors (bathroom and kitchen) but by the time you weigh up the costs I may as well buy one of these:
    m.ebay.co.uk/itm/281166812519?nav=SEARCH

    I simply want an extract from the bathroom and kitchen up to the attic and a single inlet back into the landing ceiling or maybe the attic bedroom.

    I'd like to know what would I need to control the system? Some form of humidistat or co2 sensor in both rooms would be useful, would this be easy to wire up?

    As for a condensate drain, can I use 22mm barrier pipe and somehow connect it into the bath waste? What fitting?

    As for the exhaust and supply can these just be fed from the loft space or must they go out to a roof slate?

    Any similar priced alternatives or ideas?
    • CommentAuthortony
    • CommentTimeJan 22nd 2015
     
    15mm to gutter would be easier, cant feed both to from the loft, I would do neither but you should not vent it into your loft.

    Control may be best with a variable speed timer and boost button.
    • CommentAuthoratomicbisf
    • CommentTimeJan 22nd 2015 edited
     
    For the condensate I used a 40mm solvent weld T (http://www.toolstation.com/shop/Plumbing/d20/Plastic+Solvent+Weld/sd2885/Solvent+Weld+Tee/p81661) teed into the bath waste, then a 40mm-21.5mm reducer (http://www.toolstation.com/shop/Plumbing/d20/Overflow/sd2908/Solvent+Weld+Overflow+Reducer/p47692) with the 21.5mm solvent weld overflow pipe going into that (http://www.toolstation.com/shop/Plumbing/d20/Overflow/sd2908/Solvent+Weld+PVC+Overflow+Pipe+30m/p19466 - available as singles, but doesn't seem to be listed online).

    Pretty easy to do in itself, but does depend on having a suitable route. I was lucky as our internal walls are all studwork so coould put it in that and under the bath.

    Ed
  4.  
    Posted By: tony15mm to gutter would be easier

    condensate drain piped to the gutter could / would / will freeze up in the winter. Best to route it within the heated envelope to an internal drain.
  5.  
    Okay so drain side seems easy, cheers ed

    How would I do the exhaust, and inlet then?

    Variable speed timer with boost, can this be done with humidistat or say co2 controls?
    • CommentAuthorcjard
    • CommentTimeJan 22nd 2015
     
    Posted By: Victorianecoby the time you weigh up the costs I may as well buy one of these


    2 of those, surely?
    • CommentAuthorcjard
    • CommentTimeJan 22nd 2015
     
    Posted By: VictorianecoHow would I do the exhaust, and inlet then?


    Couple of holes in the nearest wall, 1m apart
  8.  
    Why two? Would I just not use a tee?
  9.  
    When you say put in the wall 1m apart, why not put to a slate vent 1m apart?
    • CommentAuthorcjard
    • CommentTimeJan 23rd 2015 edited
     
    OK, slate vent. I don't think it matters too much, but I dare say that the wall might suffer less from the risk of water ingress, won't need bends in the ducts, and will suffer less from wind-flowing-over-pitched-surface related increased air velocities causing greater pressure fluctuations

    Your inlet and exhaust need to access the outside world separately. The manufacturer of your car went to great lengths not to connect the air intake for the engine, to the exhaust pipe and then have a T branch off. Similarly if the manufacturer of your MVHR thought they could get away with one supply/exhaust pipe that they tee off of internally for supply and exhaust, then your MVHR would have only 3, or 2 spigots rather than 4. Think of your MVHR as one pipe that comes in from the outside world and another pipe that goes to the outside. In the middle the two pipes interlace, kinda like when you clasp both hands together with fingers interlocked. That's where the exchange of heat is done, but these two airstreams, in and out, must never mix. The exhaust air must blow away in the wind and fresh air must be drawn in, hence 2 pipes, hence why MVHR boxes have 4 connectors (they're paired up: if you blow into connector 1, your breath comes out of connector 3. If you bow into 2, it comes out of connector 4. The air streams never mix)
  11.  
    Or to put it more simply you wouldn't mix what you pass out with what you ingest now would you.....
    • CommentAuthorslidersx200
    • CommentTimeJan 23rd 2015 edited
     
    Ideally you would have more than 1m separation between intake and exhaust vents, but if space is at a premium you could try this:

    http://www.proair-systems.co.uk/products/proair-fex-terminal/

    You definitely do not want to "T" off the same duct or vent the exhaust into the roof space. Single room HR units may also be worth considering if you don't intend to connect a duct to every room.
  13.  
    The tee I referred to was for the kitchen and bathroom.... Not exhaust and inlet
  14.  
    I have two disused chimneys in the loft space, could I utilise these?
    • CommentAuthorcjard
    • CommentTimeJan 27th 2015
     
    Sure. Do they exit more than a metre apart? How tall are they? The pipe would probably need to go all the way to fresh air and be capped to prevent rain getting in. Note that adding length to pipes impacts on airflow and the longer the pipe the more chance of condensation forming. You'll need to consider insulating the pipes inside the chimney as well as from unit to chimney

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