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Mechanical ventilation heat recovery retrofit for old house

SchrodingersCat

Hi,
We have a stone house built in the early 1950's. The walls at this time were thick with a rubble infill and no cavity, built with lime morter and not cement. Over the years, we have installed double glazing, a mad load of attic insulation, and sealed as much as we can (bar some room vents). We dont have a BER rating, and I would guess that we would still be pretty far down the scale.

We have found that we are getting efflorescence under the paint on some internal walls, and black mould on damp rooms such as the toilet. We are also getting mould in semi enclosed areas such as the corners of bedroom wardrobes.

To discount radiator pipe leaks, I turned off the inlet to the tank for a few days and found no drop in the level.
I have checked the pointing between the blocks on the external walls and found nothing noticeable.

We have a cheap hygrometer that is telling us that the average dampness of the air is ~70-75% with a peak of 84%. Opening a window brings this down to ~65%, a down a bit more using a dehumidifier.

This would tell me that the dampness is probably coming from the air from "wet" rooms such as the shower and toilet, and probably from cooking in the kitchen too. In particular as the dampness occurs on internal walls too, not just externally facing ones.

As such, I am wondering what we could do to help resolve this issue. Would there be any benefit in a retrofitting a Mechanical ventilation heat recovery system/ ductless system using a DIY kit? Would anyone have any suggestions?

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Idbatterim

Why not just ventilate those rooms more? Open a window in bathroom if possible when showering etc and leave it open for a while after. There are vents that detect moisture in air and run until it reduces to a certain level...

SchrodingersCat

Idbatterim wrote: »

Why not just ventilate those rooms more? Open a window in bathroom if possible when showering etc and leave it open for a while after. There are vents that detect moisture in air and run until it reduces to a certain level...

Thanks for the response. Yes, I could do that. My first plan was to add in a simple extractor fan until I heard about MVHR & DCV. I thought that they might be more energy efficient that simply pulling the warm humid air out of the wet rooms and kitchen.

Calahonda52

I would go MVHR and if RH is an issue maybe fit a cooling coil on the intake iff the outside air can get very humid, in summer, depending on location.
The age of the house points to it benefiting from MVHR

Alf Veedersane

Calahonda52 wrote: »

I would go MVHR and if RH is an issue maybe fit a cooling coil on the intake iff the outside air can get very humid, in summer, depending on location.
The age of the house points to it benefiting from MVHR

I would have assumed, rightly or wrongly, that the airtightness wouldn't be at a level that would suggest MVHR is the right option and DCV with passive humidity 'controlled' vents might be more suitable

Calahonda52

Alf Veedersane wrote: »

I would have assumed, rightly or wrongly, that the airtightness wouldn't be at a level that would suggest MVHR is the right option and DCV with passive humidity 'controlled' vents might be more suitable

From your post I got the impression it was pretty tight except for the wall vents.
What state are the external doors at?
The passive RH yokes are all fine and dandy but what happens in internal rooms with no sensor?
In any event the MHVR gives u maybe 80% cost recovery, and if run at a low flow rate except when boosted for wet room, I don't think the extra air infiltration would be a hugh issue, given what you are faced with.
The key is the selection of a quality unit with good controls and not some glorified pair of fans

SchrodingersCat

Thanks for the informative replies. No, I wouldnt think that the house would be particularly air-tight. The doors for example are ancient solid timber ones that are pretty much impossible to fit to an airtight level in the changing temperatures and weather.

So without air tightness, MVHR is useless? I would have thought that at worst, it would give similar performance as DCV by simply expelling the warm humid air. At best, as it is capturing the heat from the air before expelling it, which would make it easier to keep the rooms warm?

If this is the case, can anyone recommend DCV brands or models that they would be familiar with?

Thanks for your help.

Calahonda52

Are you anywhere near the Monasterboice Inn?

SchrodingersCat

Ah, no, unfortunately. :-( I am in Galway.

Alf Veedersane

Calahonda52 wrote: »

From your post I got the impression it was pretty tight except for the wall vents.
What state are the external doors at?
The passive RH yokes are all fine and dandy but what happens in internal rooms with no sensor?
In any event the MHVR gives u maybe 80% cost recovery, and if run at a low flow rate except when boosted for wet room, I don't think the extra air infiltration would be a hugh issue, given what you are faced with.
The key is the selection of a quality unit with good controls and not some glorified pair of fans

I think 80% cost recovery is ambitious for a house that hasn't a great airtightness value.

Agree on the system and controls and ultimately installation.

Calahonda52

Alf Veedersane wrote: »

I think 80% cost recovery is ambitious for a house that hasn't a great airtightness value.

Agree on the system and controls and ultimately installation.

I agree with the sentiment, IIRC the HR% is measured at the heat exchanger.
If he fixes the front and back doors or installs a draught lobby then the A?T will improve

Alf Veedersane

Calahonda52 wrote: »

I agree with the sentiment, IIRC the HR% is measured at the heat exchanger.
If he fixes the front and back doors or installs a draught lobby then the A?T will improve

It will improve but my point is that we just don't know how good or bad it is or where the heat loss is. AT is just such a difficult element to address and varies from house to house. I had info on some houses that were retrofitted with EWI and had AT tape put around new windows and doors and the result AT didn't improve anything like I had expected.

Not saying MVHR isn't the way to go here. Just I'm not sure what the most appropriate solution is without knowing more. That said, I'm not professing to be an expert...its just my own rationale

Calahonda52

Alf Veedersane wrote: »

It will improve but my point is that we just don't know how good or bad it is or where the heat loss is. AT is just such a difficult element to address and varies from house to house. I had info on some houses that were retrofitted with EWI and had AT tape put around new windows and doors and the result AT didn't improve anything like I had expected.

Not saying MVHR isn't the way to go here. Just I'm not sure what the most appropriate solution is without knowing more. That said, I'm not professing to be an expert...its just my own rationale

Agree 100%, we don't know.
I don't think DCV will work well here due to walls breathing all the time, especially the intern ones

Alf Veedersane

Calahonda52 wrote: »

Agree 100%, we don't know.
I don't think DCV will work well here due to walls breathing all the time, especially the intern ones

We dont know how many internal rooms there are either or if there are any.

I'm not sure why you think DCV wouldn't work. Not trying to be contrary at all here either...just trying to understand your point

MicktheMan

OP a simpler (and cheaper) solution to start with might be a long life continuously running Mechanical Extract Ventilation system (MEV) maybe with an automatic rh controlled boost function. Perhaps a single unit ducted via the attic to the "wet" rooms (kitchen/bathrooms) depending on the layout. Make sure all ducting in cold space (attic) are insulated properly. This may well solve your problem without the expense of more complicated systems.