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MVHR Not venting kitchen air

Discussion in 'Plumbing and Central Heating' started by HenryGregory, 12 Aug 2019.

  1. HenryGregory

    HenryGregory

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    Hi,
    My new build is a year old last month. I have been battling for a year now to get snagging issues resolved. It has become a second job to me.

    The property benefits from a MVHR. The kitchen has a MVHR suction pipe in the ceiling. There is a boost switch on the wall. There is an extractor above the cooker hob however it recirculates the air rather than extracting it out of the kitchen meaning the MVHR has sole responsibility for sucking up moisture and food smell.

    In short, it is not working correctly. Last week, it was 26 degrees outside, my kitchen windows were covered with condensation and kitchen unit cupboard draws dripping with condensation. The floor wet with condensation. I was cooking a pan of pasta for one. The MVHR was on boost and it made no difference.

    I have explained all of this time and time again to builder but they say it is not something they class as a defect so I am on my own.

    Can anyone advise me on what I can do. It has actually put me off of cooking and I have been eating ready meals because of the heat and moisture caused by cooking a small and simple meal. Kitchen is about 2.5 by 3mtrs square so not all that large.

    Thanks in advance.
     
  2. muggles

    muggles

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    Would need much more info to be able to diagnose. You'd be better off getting an independent MVHR expert to come and assess your system I think
     
  3. Harry Bloomfield

    Harry Bloomfield

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    Cooker hoods are much more functionally useful if the actual extract air to outside. Is the MVHR just making a lot of noise, or does it actually pull air out of the room? Can you perhaps do a simple smoke test, with some smouldering paper held up to the vent, to prove it is or not working. It be the duct doesn't actually go anywhere.
     
  4. JohnD

    JohnD

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    then it is just an ornament and performs no useful function.
     
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  5. Gasguru

    Gasguru

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    Can't you open a window or is it an internal kitchen. I trust you are cooking with just sufficient heat and a lid on...I say this as 20 years of working in homes shows that very few have any common sense.
    As mentioned I would check the MVHR duct is actually connected and functioning.
    The hob extractor should have a carbon filter to scrub the air of odours whilst set up for re-circulating mode but it's probably better being routed to the outside.
     
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  6. Madrab

    Madrab

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    Unless it has charcoal filters as well as the fine mesh grease filters installed ... ;)
     
  7. Madrab

    Madrab

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    Oops, just realised @Gasguru mentioned that at the end of his post.
     
  8. HenryGregory

    HenryGregory

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    Thank you everyone for your replies.
    I totally agree, a kitchen extractor that doesn't vent out is a total waste of time, and I was quite surprised they had not vented out as it would have barely cost the builders anything to do this.

    I am in shock that they have washed their hands of this and I am not going to let them get away with it.

    I am not sure if the extractor has a charcoal and or grease filter, I will check this out and let you know. Whatever is on it, it is still in brand new condition. I keep everything very clean and tidy.

    What do you guys think of this as a first step to moving forward with this...

    I have got my hands on some smoke pellets. I was going to set one up in the kitchen, put the MVHR on boost and see if it clears the smoke?
    I don't want to mess the MVHR up though as obviously, some of the smoke generated will be sucked up and pass through it.
     
  9. stem

    stem

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    I your case the kitchen hood won't vent outside, because the whole idea of a heat recovery system is that in the winter as much as possible of the air entering and leaving your property goes through the heat recovery system. A cooker hood vented outside would defeat the object by sending the warm air straight outside and loosing the heat.

    As has been said the cooker hood should be fitted with grease and odour filters and just used at times of maximum 'smell generation' for example when cooking a steak, or frying chips on the hob. After cooking and the hood is switched off, the heat recovery system will continue to remove the air from the kitchen and replace it with fresh air brought in from outside.

    From what you say it would appear not to be doing so, so some investigation is needed. If you were to put a single piece of kitchen towel over the extract vent, the suction should be strong enough to hold it there, if it isn't then something is wrong, difficult to say what without inspecting it. maybe the system isn't balanced properly so enough 'suction' isn't reaching the kitchen, the extract fan has failed, or maybe the kitchen duct isn't connected to anything at the other end.

    The fresh air that is reintroduced elsewhere should be able to permeate its way back to the kitchen somehow to replace what has been sucked out.
     
  10. SFK

    SFK

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    Henry
    In response to your comment "I don't want to mess the MVHR up though as obviously, some of the smoke generated will be sucked up and pass through it."

    The smoke from the smoke bomb is not going to damage your MVHR, And note that it is currently moving dust and smoke, water and fat vapour, all of which are much muc more damaging than the smoke bomb.

    When you set off smoke bomb, check to see if room is being cleared (which it should), check to see if smoke is leaking from pipes (which it should not), check to see if smoke leaving from where MVHR vents to outside (which it should and be equal to the amount of smoke entering vent in Kitchen).


    ALSO -- Am I correct or wrong in saying that you are NOT supposed to have a Kitchen extract fan if you have a MVHR. So the kitchen extract that Henry has is correct to be re-circular? All because a kitchen extract fan could overpower the extraction of the HVHR. <<< happy to be told I am wrong on this.

    (Sorry sten, I just saw that you said the same as me).
    SFK
     
  11. Gasguru

    Gasguru

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    A healthy inside air quality should always trump the necessity to save energy..so ignore any misguided building regs. (even the Grenfell amendments have issues).

    See if it's possible to have the hob extractor installed to extract externally. Any room heat loss during cooking will be offset by the heat input from the hob.

    If the property has been built with any quality the heat loss from the room will be minimal and if the MVHR is not optimal with hob use extraction then so be it.
    What you want to avoid is the possibilty that the MVHR is being contaminated with cooking vapours containing oils...that's sure to clog the filters and ducts.

    As I've said before the majority of customers I see have little common sense when cooking...the heat is set too high, pan lids are not utilised and windows not opened and until the basics are carried out there is little hope.
    I've lost count of the time I've seen water dripping off unit fronts...
     
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  12. stem

    stem

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    In the summer when you don't need heat recovery, it's fine to open windows etc, but in the winter the fundamental basic principal of the heat recovery system is that it is a balanced system meaning that all of the air coming in and out of the property in equal quantities passes through the heat exchanger. Upset the balance by opening windows, and / or using other ventilation systems and it will not work efficiently.

    I installed a MVHR system in a small well insulated property I owned 25 years ago that had only electric heating and I wanted to have fresh air in the winter without loosing my expensive heat. It worked perfectly, stale air was extracted from the bathroom and kitchen and warmed fresh air from the heat exchanger was fed into the bedrooms and living rooms. With all windows closed the system was perfectly balanced and introduced nice fresh air without heat loss or cold draughts. The bathroom condensation cleared quickly as did the cooking smells. I ran it 24/7 on the lowest speed fan setting for trickle ventilation but would boost it to full speed when bathing or cooking.

    A summer / winter switch was fitted and in the summer position the intake fan was switched off to prevent then unwanted heat recovery so it worked purely as an extraction system and I opened the windows for ventilation.

    From what you say it sounds like your system has either been badly designed, badly installed or is faulty.
     
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