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MHRV System Ducts filling with Water

  • 26-01-2022 10:59pm
    Registered Users Posts: 2,497 ✭✭✭


    Just moved into my new build house and I have a Vent Axia MHRV system installed and I was wondering do any of you guys ever have problem with your ducts filling with water from condensation.

    I have two showers, one in the main ensuite and the other upstairs which my 2 teenage sons use. Now both of them could spent up to a half hour EACH in the shower at least once a day if not twice a day.🙄🙄 Now I do also have a good plumbing system with a 3 bar pump hooked up to a 300 liter tank that never seems to get cold...... so there is no incentive for them to get out.

    To be honest I dont want to on their case as we built the house to enjoy it and I dont want to be the mean dad telling them to get the f**k out of the shower you are wasting money etc. Money isn't the issue (not really!)heating all the water, its the MHRV system cant handle the amount of steam that these showers are putting out for the length of time they are in there. (well that's my thought) After every shower its like a steam room water dripping off the wall and the ceiling and there is so much it hasn't time to recover until the other fella gets into it.....In our shower its not an issue as I probably spend 10 mins and the wife would only spend a bit more than me. But we have no issue with the wall dripping with water.

    I got the people out who installed it and they discovered the duct coming out from their bathroom was full of water where there was a dip in the ducting. He took the dip out and checked the air flow rate and he said we should be good now. That was about a week ago and now I can hear one of the ducts is full again (there is a thumping sound where the water is lapping)

    Anyway any of you guys had similar problems.....

    6.1kWp south facing, South of Cork City


  • Registered Users Posts: 2,876 ✭✭✭Borzoi

    Couple of questions.

    What is the flow rate from the bathroom?

    Is there a way for fresh air (from another room) to flow into the bathroom when the shower is on?

    Is the extract duct insulated?

  • Registered Users Posts: 2,497 ✭✭✭ECO_Mental

    The MHRV dude said 6 litres per min?? I think that's what he set it at. He also upped the boost flow a few percentage points but to be honest I don't have a remote boost button its on the unit in the garage and 9 times out of 10 its never switched on as they wont do it and I forget most of the time

    Fresh air into the room only come from under the door...from the corridor

    The ducts are not insulated but they are under the insulation in the attic.

    6.1kWp south facing, South of Cork City

  • Registered Users Posts: 2,876 ✭✭✭Borzoi

    Bathrooms should be 6 Air changes per hour (15l/s is also an acceptable measure)

    The gap under the door should be 10-12mm (approx 1/2 inch)

    The lack of insulation is allowing the shower steam to condense in the duct - it's the real issue.

  • Registered Users Posts: 301 ✭✭spose

    Is the unit ramping up when the shower is running? There shouldn’t be condensation running down the walls. Have vent axia as well. We’d regularly have 3 kids in the shower after each other, maybe not for as long as yours but would still barely be condensation on the mirror. Once the shower is turned on the fan speed starts increasing and would level off about 50%. I never boost it and just rely on the humidity control.

  • Registered Users Posts: 33,932 ✭✭✭✭listermint

    Sounds like an airflow problem as above check your door gaps and the insulation on the ducts.

    But also tell them to get the fk with half hour showers. Bad habit they'll have that expectation everywhere they go. Tis a luxury not expectation ;)

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  • Registered Users Posts: 2,497 ✭✭✭ECO_Mental

    The ducting is laid underneath all the attic insulation so it should not be cold but I need to double check that myself. The door to the bathroom would have a tight enough gap at the bottom of the door (although its around the 10mm) and the rest of the edges are tight so it might not be getting enough fresh air. My system has a humidity sensor attached but it not going to boost when they have a shower I thought it was supposed to alright.

    My normal airflow rate is 45% and the boost is set at 58% (it was 55%) but the MHRV guy cranked it up a bit when he came out last week to check it.

    Regarding telling them to get the f**k out of the shower I would love to but.....I would rather see if there was a mechanical reason first than take on that political war 😥

    6.1kWp south facing, South of Cork City

  • Registered Users Posts: 301 ✭✭spose

    45% for normal is very high I’d say. Would have thought standard is 30%. And if it’s not picking up the humidity then obviously somethings not right with it. You sure unit is right model/size for the house?