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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Rod

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11:32 AM, 6th January 2024, About 10 months ago

Reply to the comment left by SupaSarge at 06/01/2024 - 10:22
Please provide the basis for making this statement, eg legislation or building regs and provide supporting link if possible

"Listed buildings will soon be permitted to retrofit double glazing into sash windows"

Andrew Rudge

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11:34 AM, 6th January 2024, About 10 months ago

Reply to the comment left by Slooky at 06/01/2024 - 11:04
Getting rid of the moisture laden air would be better than trying to create warmer surfaces, as the relative humidity would just build and find somewhere else to condense on.
I don't know a great deal about listed buildings, I've heard they will allow thin section double glazing, but if your in a conservation area as well then your not going to be allowed even that.
I've seen mixed results with secondary glazing, they tend to leak air and you just end up with condensation inside.

You clearly have the property's best interest at heart and I think your first thoughts regards MVHR is the way to go.

As an aside, 3.6M sashes are impressive, I'd hazard your flat is less a flat and more a piece of architecture, your a far braver man than me!

Andrew Rudge

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Rod

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12:03 PM, 6th January 2024, About 10 months ago

Reply to the comment left by Andrew Rudge at 06/01/2024 - 11:53Thanks. I had already read it when I searched for anything which supported SupaSarge's comment.
Informative but dated 2017 so certainly nothing to support upcoming changes.
Slight tangent to the current conversation - has anyone used infrared heating, especially to address a situation such as this?
I know they don't recommend facing it at windows, but heavy wooden blinds such as plantation shutters style or traditional shutters would minimise IR loss through glass.

Slooky

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12:27 PM, 6th January 2024, About 10 months ago

Reply to the comment left by Andrew Rudge at 06/01/2024 - 11:34
3.6m these are the biggest 3 the rest are slightly smaller. My husband is the braver man!🙂

Andrew Rudge

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12:32 PM, 6th January 2024, About 10 months ago

Reply to the comment left by Slooky at 06/01/2024 - 12:27
Slooky, my apologies for being presumptuous.

Andrew Rudge

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12:36 PM, 6th January 2024, About 10 months ago

Reply to the comment left by Rod at 06/01/2024 - 12:03
It's not a solution I'd entertain because the introduction of heat, by any means, only increases the airs capacity to hold more moisture, which is fine if it stays at that elevated temperature. But it won't stay warm, and as the temperature drops and meets the dew point your back to square one.

SupaSarge

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18:40 PM, 6th January 2024, About 10 months ago

Reply to the comment left by Slooky at 06/01/2024 - 11:04Hello Slooky
Yes, with acrylic panels (esp when fitted to south facing windows) when either the width or height of each sash starts getting over about 1.1m you need to be cautious as thermal expansion can lead to the panels poping from their magnets on sunny days (esp when left on all year round).
Those sashes of yours are monsters but I bet they're gorgeous ☺️
I only found this post this morning - so great to read such well informed opinions.
Here's the latest on the government's inevitable policy easing: (+@Rod!)
https://www.telegraph.co.uk/news/2024/01/03/planning-rules-relaxed-allow-heat-pumps-solar/
But, like I say I really wouldn't recommend DG sash retrofits for a bunch of reasons (false panacea unless you go for v. high end units exceptionally well fitted, which totally kills payback economies). Draughtproofing sashes windows typically solves half the combined thermal heat loss (conduction & radiation) but with yours having such sizeable glazed areas the conduction loss through glass will be more significant per window.
As you say the moisture problem is the one to solve first and unlike DG will be worth the investment. Just need to get the MVHR solution right ....
With apologies if this has already been explained elsewhere in the trail, but are you intending to expel air (+ intake air) from the roof void or outside the building?

Ararat

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20:14 PM, 6th January 2024, About 10 months ago

Reply to the comment left by David Moreton at 02/01/2024 - 11:10
yes, we have fitted the Nuaire positive pressure system in a number of problem properties, had no trouble since. i read that they use them successfully in homes after flood damage, and apparently better than dehumidifiers - plus less likely to get turned off by tenants concerned about energy bills. We found that if we turned the fan speed down a bit so that it was not noticeable, it was more acceptable to them.

Slooky

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21:09 PM, 6th January 2024, About 10 months ago

Reply to the comment left by SupaSarge at 06/01/2024 - 18:40
We have been told we can't use the loft space for air intake because we have an internal gutter. So when the ducts enter the loft a flu/duct/vent or whatever the name is will exit the roof and go outside to take fresh air. So I assume stale air will exit outside as well as they pass each other in the heat exchanger.

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