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Retrofit MHRV

  • 12-02-2020 3:43pm
    #1
    Registered Users Posts: 793 ✭✭✭ metricspaces


    I have an A3 rated house and wondering if it is possible to retrofit MHRV?

    House is two story semi-detached, timber frame construction of 120sqm. I've got hole-in-the-wall vent in living room for sealed stove and ventilation in house is via trickle vents in the windows. Three bathrooms and utility room have extractor fans. Kitchen has extractor over hob.

    Is this possible?
    - Install MHRV unit in attic
    - Remove extractor fans in 2 upstairs bathrooms and feed with MHRV unit
    - Feed 3 bedrooms upstairs with MHRV
    - Take one feed from MHRV down from attic, through hot-press, and into kitchen\living room area (open plan 40sqm area)
    - Seal up all trickle vents in windows
    - Leave extractor fan in downstairs bathroom and utility room
    - Leave hole-in-the-wall vent in living room area
    - Leave kitchen hob extractor (external)

    I know you can get decentralized system. But I've read they are more noisy and they would require drilling several holes in external walls which I'd rather not do.


Comments

  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    Did you not just build a house?


  • Registered Users Posts: 793 ✭✭✭ metricspaces


    BryanF wrote: »
    Did you not just build a house?

    No. I'm looking to retrofit the mhrv. Wondering how possible it is.


  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    Tell us more about the house? Have you considered an air-test? Having direct extract without heat recovery from the wet areas kind of defeats the purpose of putting in mvhr? Difficult to balance

    (Edit: you generally supply to living and bedrooms and extract from kitchen and bathrooms)


  • Registered Users Posts: 793 ✭✭✭ metricspaces


    BryanF wrote: »
    Tell us more about the house? Have you considered an air-test? Having direct extract without heat recovery from the wet areas kind of defeats the purpose of putting in mvhr? Difficult to balance

    (Edit: you generally supply to living and bedrooms and extract from kitchen and bathrooms)

    My airtightness is 4.78 m3/hr/m2 which I understand should be good for MHRV. My main objective is to get rid of trickle vents in windows as I'm in a higlhly exposed area. Avoiding heat loss would also be nice.

    Extracting from two bathrooms upstairs will be easy as I just remove current extractor fan and replace with pipe for MHRV plus I've easy access from attic. Similarly feeding bedrooms is easy with access from attic.

    Problem is with downstairs in terms of getting pipe down from attic. Going through hotpress will get me to wall of kitchen (opposite side to extractor fan on cooker). Kitchen/living room is all one space.

    I need to keep the hole in the wall vent in living room for stove. Does that kinda negate getting a ventilation system? Also can I keep extractor hood which is connected to outside vent or that would need to change.


  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    a stove that’s not room sealed, and downstairs bathrooms with direct mech extraction.
    Mvhr sounds dodgy.


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  • Registered Users Posts: 793 ✭✭✭ metricspaces


    BryanF wrote: »
    a stove that’s not room sealed, and downstairs bathrooms with direct mech extraction.
    Mvhr sounds dodgy.

    It's a 5kw stove, so it's not possible to have mhrv unless it's room sealed? Once mhrv system is feeding enough air wouldn't it be ok?

    Downstairs toilet & utility room have extractor fan. As usual setup comes on when turn on light. What problem would it cause to have mhrv in rest of house & leave these two room as-is?


  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    BryanF wrote: »
    Having direct extract without heat recovery from the wet areas kind of defeats the purpose of putting in mvhr?

    * Difficult to balance *

    (Edit: you generally supply to living and bedrooms and extract from kitchen and bathrooms)
    .


  • Registered Users Posts: 642 ✭✭✭ bemak


    been doing a bit of research on this as we have a condensation issue in our house (bought last year). Our house is 70s so a lot different to an A3 rated home.

    Unless you are going for a fully sealed box, MHRV won't be as efficient. By right, in an air-tight house, the stove would have it's own piped air supply so that it's not relying on air from the room (which wouldn't be there to the extent needed given it's air tight). The fact that the stove is already installed means it needs the vent on the wall. You can still install a MHRV system but it won't be efficient so you'd question the need for it then if it's not going to do what it should do.

    I'm probably going to get a DCV system installed in our house to resolve the humidity issue. I had looked at the Lunos system (there is a company in Galway supplying them) which appears to work like a DVC system except there's an element of heat recovery involved as well. However, I'm yet to read any reviews online about them and they're quite expensive so I might just stick with a more tried and tested model.

    In short, in your case, yes you can install MHRV but it won't be efficient considering you have a gaping hole on an external wall for your stove.


  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    I’ve DCV installed in wet rooms/kitchen

    It will change a houses air movement dynamics

    Which needs to considered with existing chimneys / flues / open fires / stoves / vents etc


  • Registered Users Posts: 642 ✭✭✭ bemak


    BryanF wrote: »
    I’ve DCV installed in wet rooms/kitchen

    It will change a houses air movement dynamics

    Which needs to considered with existing chimneys / flues / open fires / stoves / vents etc

    did you retrofit it to sort a problem?


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  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF


    bemak wrote: »
    did you retrofit it to sort a problem?
    Not really. Added it as part of extension/upgrade.


  • Registered Users Posts: 584 ✭✭✭ ravendude


    BryanF wrote: »
    I’ve DCV installed in wet rooms/kitchen

    It will change a houses air movement dynamics

    Which needs to considered with existing chimneys / flues / open fires / stoves / vents etc

    Did you get/test to a particular airtightness level for this? My understanding is for DCV you need pretty good airtighness also.

    I am putting in plain centralized continuous MEV to wet rooms with humidistat boost, - was thinking about DCV and might upgrade in the future


  • Registered Users Posts: 584 ✭✭✭ ravendude


    bemak wrote: »
    been doing a bit of research on this as we have a condensation issue in our house (bought last year).

    Are you getting condensation in particular spots? it may well be that you have specific construction issues like cold bridges


  • Registered Users Posts: 2,095 ✭✭✭ Yellow_Fern


    BryanF wrote: »
    I’ve DCV installed in wet rooms/kitchen

    It will change a houses air movement dynamics

    Which needs to considered with existing chimneys / flues / open fires / stoves / vents etc

    How is noise wise?


    Overall the OPs case is interesting. How easy to get to A3 with trickle vents like the OPs I wonder?


  • Registered Users Posts: 793 ✭✭✭ metricspaces


    ravendude wrote: »
    MEV to wet rooms with humidistat boost

    What product did you get with humidistat boost? Something like this https://www.amazon.co.uk/Envirovent-SIL100T-Silent-Bathroom-Extractor/dp/B0080XNKQ0 ?

    With humidistat is the fan humidity sensor active continuously and it turns on the fan extraction when humidity goes above a certain level and turns off fan exctraction when humidity falls back below the specified level?

    Or does the humidity sensor only kick in when fan is activated e.g. light turned on in room, PIR sensor detects movement etc?


  • Registered Users Posts: 584 ✭✭✭ ravendude


    What product did you get with humidistat boost? Something like this https://www.amazon.co.uk/Envirovent-SIL100T-Silent-Bathroom-Extractor/dp/B0080XNKQ0 ?

    With humidistat is the fan humidity sensor active continuously and it turns on the fan extraction when humidity goes above a certain level and turns off fan exctraction when humidity falls back below the specified level?

    Or does the humidity sensor only kick in when fan is activated e.g. light turned on in room, PIR sensor detects movement etc?

    This:
    https://www.bpcventilation.ie/vent-axia-sentinel-multivent-humidity-2715
    The unit is always on at a very low power and adjusts up automatically if humidity increases
    It is a centralized, ducted system


  • Registered Users Posts: 30,654 ✭✭✭✭ listermint


    ravendude wrote: »
    This:
    https://www.bpcventilation.ie/vent-axia-sentinel-multivent-humidity-2715
    The unit is always on at a very low power and adjusts up automatically if humidity increases
    It is a centralized, ducted system

    What's the point in something like this if you can't reuse the heat removed . Is it not just a fancy extractor fan ?


  • Registered Users Posts: 793 ✭✭✭ metricspaces


    ravendude wrote: »
    This:
    https://www.bpcventilation.ie/vent-axia-sentinel-multivent-humidity-2715
    The unit is always on at a very low power and adjusts up automatically if humidity increases
    It is a centralized, ducted system

    Thanks! Would something like this do the same job? https://www.powerdiscount.co.uk/vent-axia-477436b-vasf100ht-100mm4-ducting-silent-humidity-timer-fan---redesigned-2020-edition-74966-p.asp

    These seem like a good idea if the humidity sensor is accurate enough. Plus they claim to have a very low operating noise level which is nice too.

    I see they do a heat recovery one too similar to other brands like LUNOS I'd imagine https://www.vent-axia.com/range/lo-carbon-tempraselv


  • Registered Users Posts: 584 ✭✭✭ ravendude


    listermint wrote: »
    What's the point in something like this if you can't reuse the heat removed . Is it not just a fancy extractor fan ?

    The point is its costs hundreds vs many 1000s of euros investment for MVHR, helps air quality, and are suitable for retrofit houses with existing heating system with mproved airtightness but without continuous membranes etc that do not have adequate air tightness for MVHR. MEV is also very simple.

    Plenty of irish houses have serious problems with ventilation that get much worse with even modest improvement in airvtightness


  • Registered Users Posts: 793 ✭✭✭ metricspaces


    ravendude wrote: »
    The point is its costs hundreds vs many 1000s of euros investment for MVHR, helps air quality, and are suitable for retrofit houses with existing heating system with mproved airtightness but without continuous membranes etc that do not have adequate air tightness for MVHR. MEV is also very simple.

    Plenty of irish houses have serious problems with ventilation that get much worse with even modest improvement in airvtightness

    This system just extracts air from wet-rooms? How are you getting fresh air into the house?

    As the humidity sensor is in the unit, this means that you've only one sensor? So the extraction will increase in every wet-room even if humidity is rising in only one wet room?

    What is the benefit of having a single system like this versus the individual extractor fans I linked to which have humidity sensor. Same end result right?

    Like all these ducted systems, they only suit retrofits in bungalows? Bit of a nightmare to extract from downstairs rooms in a two story house?

    BTW I'm not knocking your system...just trying to understand the various options, pros\cons etc.


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  • Registered Users Posts: 30,654 ✭✭✭✭ listermint


    ravendude wrote: »
    The point is its costs hundreds vs many 1000s of euros investment for MVHR, helps air quality, and are suitable for retrofit houses with existing heating system with mproved airtightness but without continuous membranes etc that do not have adequate air tightness for MVHR. MEV is also very simple.

    Plenty of irish houses have serious problems with ventilation that get much worse with even modest improvement in airvtightness

    but that system seems to be just a ducted multiple extraction unit. e.g shared between humid rooms. Where is the return coming in ?

    Seems like a fancy extractor with a humidity sensor on it. maybe im missing something ?


  • Registered Users Posts: 584 ✭✭✭ ravendude


    listermint wrote: »
    but that system seems to be just a ducted multiple extraction unit. e.g shared between humid rooms. Where is the return coming in ?

    Seems like a fancy extractor with a humidity sensor on it. maybe im missing something ?

    Yes, ultimately.
    But, its several hundred euro so at the vey bottom end of the scale for centraiized system,.

    Also, I am doing extension/renovations at the moment so ducting is now in and can be upgraded to DCV later, with a low investment. Unit + ducting kit all for circa 500 euro.
    There is no "return". Wetter air is simply extracted and drier air is pulled through from drier atreas in the house so there is a very slow but continuous ventilation through the house.
    This unit has just one humidistat which is a bit of a weakness, but other units can have humidistat sensors in each duct inlet. Ducts openings can be adjusted however to be opened out or closed variably to control intake on each duct.

    Its certainly not a perfect system but its simple and comparatively reasonable, and does have some pros


  • Registered Users Posts: 4 RikKav


    Hi Bemak - Did you go with the Lunos system - I am looking to instal DCV system. Just wondered if you found any feedback anywhere.



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