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MEV or MVHR - that is the question!

  • 16-06-2025 08:20AM
    #1
    bemak
    Registered Users, Registered Users 2 Posts: 918 ✭✭✭


    I have started renovation works to an old stone farmhouse (150sqm) which involves the addition of a two-storey extension. We've decided to go down the route of UFH on both floors which will be run with a traditional oil boiler for now. We've allowed provisions for a HP in the future. The heating will be supplemented by a back boiler in a solid fuel stove.

    As the existing stone walls will be rendered internally with an insulating lime render to allow moisture to escape - I want to install a good ventilation system that will help to extract moisture from the house. The preference is for the unit to go in a warm attic, from which I can duct all the rooms. As the layout of the house is quite simple, the routes are relatively straightforward. 

    The question now is, which system to go for. I've narrowed it down to MEV or MVHR. As the house is being completely gutted, I think it's likely that the airtightness will be good enough for a MVHR unit and while on paper I like the benefits of a MVHR unit over a MEV unit, I'm just wondering if it's worth the extra running cost (2 fans instead of 1). My priority is to get moisture out of the house as it occurs - so a MEV system with trickle vents in the windows will likely do the job just fine - but I don't want to be sorry later for not installing MVHR.

    Is it possible to set a MVHR unit to 'extract only' so that it would essentially work like a MEV if I wanted it to?



Comments

  • #2
    BenIrishHome
    Registered Users, Registered Users 2 Posts: 83 ✭✭BenIrishHome


    First question, why not just go Heat Pump day one? Not much more than an oil boiler.

    Secondly, the running costs of MEV and MVHR are tiny, you won't notice the difference. It's more the upfront capital costs, which probably arent a huge difference. Usually retrofitting its the hassle of running the ducts, but if you think that's simple then I'd say go for it.

    From what I've picked up… I am no expert. About to retrofit a 2000s dormer bungalow and apparently I would never be airtight enough for MVHR to be worth it, so I am basically being advised to go trickle vents and MEV.



  • #3
    bemak
    Registered Users, Registered Users 2 Posts: 918 ✭✭✭bemak


    how deep are you going with the retrofit? once the envelope is sealed you could do an airtightness test to see if you could get MVHR.



  • #4
    steamdave
    Registered Users, Registered Users 2 Posts: 183 ✭✭steamdave


    I retrofitted a 2003 bungalow with a Vent Axia Kinetic MHRV unit. The main reason at the time was to ensure the house was radon free but also to keep the inside of the house moisture free. No, it wasn't airtight and so probably wasn't working as efficiently as it could be, but it certainly kept the house dry and supplied with warmed air. In the hot weather, the fans were reversed if the indoors temperature was warmer than outside (nighttime especially).

    Move to a different bungalow similar age without the ventilation system. Winter time the windows were streaming with condensation. We started off opening the windows but of course, all the warmed air from the central heating went out those open windows. I've got around it to a large extent by getting a dehumidifier. Much more expensive to run than the MHRV, and we don't have the fresh air coming in.

    To sum up: If you intend to stay in your house for a long-ish time, then go for the MHRV system. Don't put an air extraction vent from that system anywhere near your hob - use a proper hob extractor.

    Dave



  • #5
    BenIrishHome
    Registered Users, Registered Users 2 Posts: 83 ✭✭BenIrishHome


    https://www.boards.ie/discussion/comment/123623245#Comment_123623245

    Thanks for this. I want to do MVHR on my 2001s bungalow. Getting new windows and doors, UFH and a heat pump this month, then I'll see how we go and hope to add MVHR next year.

    Funny enough, we've been here 12 years and never had much problem with condensation or damp, even though the previous owner had blocked up ALL the vents with newspaper. Must be hella leaky house otherwise. We might do all this work and find we have a moisture problem.

    Re cooker extractor. I was told with MVHR they recommend a recirculating extractor and then a MVHR out-vent nearby. Seems ilogical to me, I'd rather have a direct vent from the cooker to outside.



  • #6
    steamdave
    Registered Users, Registered Users 2 Posts: 183 ✭✭steamdave


    https://www.boards.ie/discussion/comment/123634779#Comment_123634779

    Direct vent to outside is the cheaper and better option compared to a recirculating hood.

    Dave



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  • #7
    karltimber
    Moderators, Home & Garden Moderators Posts: 1,909 Mod ✭✭✭✭karltimber


    Question - for people that install MVHR setup on an upgraded house - what do they do with the older open vents in the rooms ?



  • #8
    Yellow_Fern
    Registered Users, Registered Users 2 Posts: 2,716 ✭✭✭Yellow_Fern


    They would be sealed. Hopefully aesthetically



  • #9
    steamdave
    Registered Users, Registered Users 2 Posts: 183 ✭✭steamdave


    I had window frame vents and Munster Joinery gave me - well, sold me - some special blanks that fitted inside the vents.

    Dave



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