Whole House MVHR

Discussion in 'Eco Talk' started by Bobby Dazzler, Aug 2, 2020.

  1. Bobby Dazzler

    Bobby Dazzler Active Member

    I think that is the right term for it.

    And I hope I'm in the right forum. My apologies for the rather long post.


    I'm in the process of renewing the roof on an old stone building in France and i want to install a whole house MVHR system, although the kitchen will not be included because it’s in a different part of the building. Also, any other background ventilation to the upstairs rooms will be restricted for a while, including windows.

    Because I have space in the eaves to run the vent pipes for the upstairs,(see diagram) I was going to install the vent pipes, splitter/distributor, and inlet - exhaust in this space.

    So I need to get on with ordering the parts or the kit quite soon.


    I intend to install the inlet and exhaust through the solivet, which is the horizontal bit under the eaves (think of it as a soffit, but there's no fascia)

    I also want to install the splitter/distributor in this eaves space. The eaves space is about 50cm X 50cm, but obviously with a sloping roof. So there's plenty of room.

    I intend to insulate above the solivet/soffit with fibre/wool insulation, and extend the roof insulation (Tri-Iso over-rafters) down to meet the junction of the roof – outside edge of eaves. I will also place EXP insulation on the outside of the upstand of the low walls between rooms and eaves space (200mm thick, block walls).

    I have done a couple of diagrams, one a cross section of the eaves space, the other a rough plan of the house.

    There will be three bedrooms and a bathroom upstairs. I will position the MVHR unit on the landing next to bathroom to allow easy maintenance.

    The building is about 20 metres long. The rooms and stairwell have vaulted ceilings.


    Comments would be appreciated plus any other hints or warnings of pitfalls.

    Cross-section of eaves space
    upload_2020-8-2_10-36-13.png


    Plan of Building and proposed pipe runs.
    upload_2020-8-2_10-37-50.png
     
  2. Bobby Dazzler

    Bobby Dazzler Active Member

    Incidentally, I only need to install the parts that are going in the eaves space, for now.
    The main MVHR unit can be bought and installed at a later date.
     
  3. HappyHacker

    HappyHacker Active Member

    I have not installed one but had planned to and done a lot of research. I would recommend getting the company you plan to buy from to do the design There are a lot of considerations to getting it right: from where does the condensate drain to prower supply and the sort, length and size of ducting to ensure adequate flows, low noise and where it will run.

    Edit: Also you need a reasonably air tight building otherwise you risk just sucking cold air in from outside or venting your hot air through the leaks making the whole system fail.
     
  4. Bobby Dazzler

    Bobby Dazzler Active Member

    Hi HappyHacker, sorry for the belated response. I was checking the post regularly for a few days, then a week goes by....
    I eventually managed the get a quote for a kit, after sending in sketches of the plan, 'cos I don't have a formal plan drawn up.
    I could only find one supplier who would deliver to me here, in France. Others would supply but I'd have to sort my own carrier. After emailng a carrier there was no response. So the only supplier (in NI) and delivery came in at nearly £3k excl VAT, excl delivery. I was expecting sub £2k.
    I would have preferred UK stuff 'cos it seems better quality than French DIY stuff.
    So I've sourced all the bits here in France from one of the DIY sheds. The whole lot came in under £1k.
    For sure there's some big differences:
    UK ducting is 2 X 75mm to each room, extraction or supply, and intake/exhaust to exterior is 150mm rigid ducting. None of the ducting is insulated, that'd be extra. The UK ducting is supposed to be smoother internal bore, even though it's spiral bound. Manifolds for supply and extraction are used. The 75mm ducting comes in long rolls, so junctions can be mostly avoided.

    On the kit I purchased (obviously there are variations) French ducting is 80mm to each room, 125mm to kitchen, spiral bound and insulated (non-insulated is also available).
    Intake and exhaust to outside is 125mm and can be flexible spiral bound insulated.
    Manifold used for supply, but all extraction comes straight off the unit. There's a 125mm for kitchen, 2 X 80mm ports for WC's and 2 X 80mm for bathrooms.
    There are exhaust manifolds available if needed. Obviously unused extract ports are blanked off. Although the kit did not include a blanking plate for the 125mm to kitchen. I used a 125mm drain pipe stop end, same size. Ducting comes in 3M, 6M or 10M cartons, so junctions might be needed, which are naff metal welded galvanised. The weld invariably rips the inner sleeve of the duct when trying to use them. So I've substituted plastic drain pipe connectors which fit into the usual connectors to the unit, Spare ones of these are readily available. So using the connectors from duct to unit in the end of the duct, other end then fits into plastic drainpipe connector, then same other end, taped for hermetic sealing and insulated.
    The kit includes: HR unit, supply manifold, supply and extract grilles for ceilings, spare blanking plates and duct connectors - €500
    Insulated ducting, bits of plastic drain pipe, external intake and exhaust grilles and in-line silencer - about €400

    The unit is D rated for energy, (again better units are available) but I'm expecting, or wanting to uprate it anyway in a couple of years. Maybe add a pre-heater, although it rarely gets that cold here, and a post unit heater for bringing the air temperature up. Electric is fairly cheaper here. But I could add any other type of heater, water from the boiler, ground source pump (which can cater for heating as well as cooling), air source pump, or solar water heating.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice