Mechanical heat recovery ventilation damp problem?

Mechanical heat recovery ventilation damp problem?

10:06 AM, 2nd January 2024, About 10 months ago 65

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Does anyone have experience with mechanical heat recovery ventilation units? I have a top floor flat with 2 bedrooms facing north, and a kitchen and sitting room facing south.

The outside walls of the bedrooms mainly the north-facing walls suffer from condensation and the humidity level at the moment is reading about 67 which is lower than I expected because the air in the bedrooms feels and smells dank. A dehumidifier has been installed for the past week.

I have had a discussion with a company that sells MHRV units and they suggested extracting the air from the hallway which is in the middle of the flat and pushing it into the bedrooms.

I am confused because I would have thought it would make sense to extract the damp air from the bedrooms and push the fresh air back into the hallway. The hallway is a U shape so the fresh air would be pushed back in on the leg of the U outside the 2 bedroom doors.

The company I spoke to had a floor plan and was aware we only had a problem on the north side of the building in the 2 bedrooms.

Any assistance will be greatly appreciated.

Slooky


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David Moreton

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18:57 PM, 2nd January 2024, About 10 months ago

Ever thought of replacing the bedroom windows with modern PVC double glazing ?

Slooky

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18:57 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by JB at 02/01/2024 - 12:11
It has been looked at and there's no evidence of water ingress. It has also been suggested the the tops of the walls could suffer if the insulation doesn't go all the way into the eaves. But our insulation was put in from below when there were no ceilings. It's the solid type which is cut and fitted between the ceiling joists. Then all taped on the edges. Probably made the flat quite airtight because the floors had new floor insulation and noise deadening stuff and then all taped with noise tape at the edges.

Slooky

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19:03 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by Rod at 02/01/2024 - 18:24
Yes I think it was for a full flat because they speak about venting out from the kitchen and the bathroom. But those rooms are fine. The bathroom has the equivalent of the cyclone 7 which is a humidistat fan so we don't need anything else in there. I did look at systems for individual rooms but I was aware that they would need to be quiet so that narrowed it down. They have some which are an all in one fan which is fitted through a hole in the outside wall with very attractive vent on the inside but the running costs were high to heat the air coming back in because they used heaters inside the fan.

Slooky

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19:11 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by David Moreton at 02/01/2024 - 18:57All the time 🙂. Would love to but it is a grade 2* listed building so we can install secondary glazing only. Apparently I have read that some people don't believe this will help with the walls. It will stop the water condensation on the windows but won't change the temperature of the walls.
HMRC and secondary glazing is another bugbear of mine. HMRC will allow double glazing to be a revenue cost even when replacing single pane glazing (i.e. an improvement) but they won't allow secondary glazing to be a revenue cost so we couldn't claim it as an expense.

Chris Bradley

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21:52 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by Slooky at 02/01/2024 - 19:11
I have UPVC windows and it doesn't stop the moisture forming- we still get condensation.

Slooky

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21:55 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by Chris Bradley at 02/01/2024 - 21:52
I was referring to secondary glazing. Apparently they recommend a large distance between window pane and secondary glazing pane - larger than which exists on double glazing. I don't have any, it's just what I have read in people's comments

Chris Bradley

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21:59 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by Slooky at 02/01/2024 - 21:55
Sorry I was just trying to point out that even with double glazing it doesn't stop the condensation, recently put heritage double glazing into replacement wooden frames and we still have condensation. Heating and ventilation is the only solution- when the tenants heat the flat no condensation, when they don't condensation and mould appears

Slooky

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22:10 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by Chris Bradley at 02/01/2024 - 21:59
No problem. Trouble is I can't blame a tenant for not wanting to leave the heating on when they are not in the flat. They have it on for an hour in the morning which is the time it takes for them to get ready for work and then approx 3 hours in the evening. It heats up quickly and the flat gets quite hot. I really just want a system which will ventilate in a nicer way than just air vents and cold drafts. If anyone has experience of such systems which use a heat exchanger which warms the incoming fresh air via the outgoing warm air which can be set to take account of humidity levels I would really appreciate some feedback.

Chris Bradley

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22:20 PM, 2nd January 2024, About 10 months ago

Reply to the comment left by Slooky at 02/01/2024 - 22:10
I wanted to put the Nuaire heated positive inflow ventilation unit, but being a listed building I wasn't allowed to vent externally and didn't have an attic option. I did have the installer out to assess and they were very good even.though we couldn't proceed- check out their website

David Moreton

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23:08 PM, 2nd January 2024, About 10 months ago

No need to vent externally, air leakage within the property is usually fine

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