MHRV indoor air quality - is it healthy or a problem?

baby fish

Just wondering about the indoor air quality of a house with MHRV

its easy to find out the efficiency of any mechanical Heat Recovery ventilation unit... after installation your expected efficiency should be around the lab test %, although probably a little less is to be expected.

sufficient ventilation can be achieved if the system has been considered during the design stage of the building allowing ducts and air vents to be correctly planned and as a result positioned in the correct position.

But what about the Indoor Air Quality when using MHRV?

Is the IAQ of a house with MHRV actually healthy?

1. What standards ( if any ) must a manufacturer meet re this very important point? - Has anybody any information on this ... I cant find anything on this.

2. In a house post installation it is easy to monitor air temp on exhaust and intake, RH of air, see if you are saving money on your heating bill etc, but what methods are available to monitor the indoor air quality of a house as the years tick by and the MHRV system gets older, dustier, as dampness and mould forms in the ducts?

CJhaughey

baby fish wrote: »

2. In a house post installation it is easy to monitor air temp on exhaust and intake, RH of air, see if you are saving money on your heating bill etc, but what methods are available to monitor the indoor air quality of a house as the years tick by and the MHRV system gets older, dustier, as dampness and mould forms in the ducts?

Why do you think dampness and mould will form in the ducts?
Moving air will tend to dry not dampen and if the filters have been properly maintained then the ducts should stay clean.
I have looked into the galv ducts we have installed and there is no mould and little dust. In the kitchen extract there is a small bit of grease/dust build up directly behind the opening, that was easily cleaned.

PROJECT K

Hi OP, firstly i am not a fan of ducted air supply so maybe i am biased - but i have researched this extensively and there are too many "ifs" and "should" when it comes to claimed performance of these systems in terms of air quality. Centralised MHRV, when designed, installed, commissioned and maintained in a building that has been specifically designed for the use of such a system (i.e. compact building, ducts with short runs, centralised unit etc) is fine - but even then i wouldnt personally take the risk. While MHRV is not by any means new, there is very little practical research on the long term air quality as these systems age and occupants get lazy about replacing filters, carrying out regular maintenance etc. If anything research to date indicates that occupant feedback is quite negative in terms of air quality - google "RESIDENTIAL VENTILATION SYSTEM PERFORMANCE: OUTCOMES OF A FIELD STUDY IN THE NETHERLANDS" - pm me if you cant find it.

There are lots of posts on here looking for the cheapest MHRV system and thats whats worrying - you get what you pay for at the end of the day, but why risk indoor air quality and your families health for the sake of saving a few euros on heating?

Also you mentioned efficiency, the claimed efficiency of some units are much higher than what will ever be attained in application so if you cant trust what they are quoting then how would you ever trust claims on air quality?.

I dont have the answer either by the way, natural ventilation doesnt work particularly well either plus you get significant heat loss as we have to comply with Part F. However, I do believe that one of the best alternatives is either decentralised heat recovery or demand control ventilation where there are no supply air ducts (other than through the wall).

I am currently on the fence between these two for my own self build but, if budget permits, most likely will opt for the more expensive DHR system or a hybrid of the two (one of the inherent benefits of DHR is its flexibility and adaptability).

I can assure you i am not a supplier/manufacturer and have no commercial interest in these systems - just an interest in my own house and a despair at many of my friends and colleagues currently building houses blindly installing MHRV ("that they got a good deal on":() with little or no understanding of the technical risks in houses that were not specifically designed to accomodate such systems.

galwaytt

PROJECT K wrote: »

There are lots of posts on here looking for the cheapest MHRV system and thats whats worrying -

Tbh - this is the issue that most people focus on. I have never, bar one, met anyone who has bought an MHRV based on specification. It has only ever been on price.

And like what you say, you get what you pay for.

buzz11

galwaytt wrote: »

Tbh - this is the issue that most people focus on. I have never, bar one, met anyone who has bought an MHRV based on specification. It has only ever been on price.

And like what you say, you get what you pay for.

what do you reckon are the key spec's that should be compared?

sydthebeat

buzz11 wrote: »

what do you reckon are the key spec's that should be compared?

http://www.boards.ie/vbulletin/showthread.php?t=2055385732&highlight=fire

http://www.boards.ie/vbulletin/showthread.php?p=61900025

baby fish

@PROJECT K

When picking a ventilation system I was won over by the idea of ventilation + heat saving + the perfect indoor air quality. I actually have/had MHRV installed but I'm in the process of removing it and I am currently looking for an alternative means of ventilation. Its a long story leading to this point but after a number of issues over the entire system left me with little confidence , I began to wonder how good actually is the air quality.... this was the final nail in the coffin.

The reason why I started this thread is to make people aware they should consider this important point , indoor air quality, don't just think of efficiency and saving money on heating.

@ CJhaughey
Why do I think dampness and mould will form in the ducts?

Its more than thinking I'm afraid, I've seen mould in them . The Cause is the Building reg with min 25mm of insulation around duct in an unheated space is not enough, mould will form. Ok its in the extract so supposedly it wont re enter the house.. but how do you know how well the supply/extract air flows are isolated within the MHRV unit ?

I was told that mould cant form while the air is moving through the duct, but this is untrue, mould will form in suitable conditions even when there is an airflow.

CJhaughey

The system I have was specced at the design stage as part of the house package.
All ducts run inside the thermal envelope and have additional insulation.
Its my belief that HRV is a good thing as along as the designers have thought it through at the design stage.
Unfortunately we have the same problem as with many other aspects of design in housing.
It is bought as one would buy a fridge or a cooker, not with an eye to how it performs long term but as a purchase that simply complies with a law or directive.

baby fish

CJhaughey wrote: »

The system I have was specced at the design stage as part of the house package..

Mine wasn't, I decided on ventilation method after design stage was finished.

CJhaughey wrote: »

All ducts run inside the thermal envelope and have additional insulation...

I can only talk about ducts in the attic, 25mm of insulation is not enough

CJhaughey wrote: »

Its my belief that HRV is a good thing as along as the designers have thought it through at the design stage.

I would sayit could be a good thing, prove it to me first though

CJhaughey wrote: »

Unfortunately we have the same problem as with many other aspects of design in housing.
It is bought as one would buy a fridge or a cooker, not with an eye to how it performs long term but as a purchase that simply complies with a law or directive.

So at the end of the day, we don't know how good the IAQ is. Is this not a bit worrying? it was for me. There is a belief it creates the perfect indoor air quality, I'm not so sure. There seems to be no evidence. I suppose you either trust it or you don't.

sydthebeat

baby fish wrote: »

Mine wasn't, I decided on ventilation method after design stage was finished.



I can only talk about ducts in the attic, 25mm of insulation is not enough




I would sayit could be a good thing, prove it to me first though



So at the end of the day, we don't know how good the IAQ is. Is this not a bit worrying? it was for me. There is a belief it creates the perfect indoor air quality, I'm not so sure. There seems to be no evidence. I suppose you either trust it or you don't.

so you installed yours in a cold attic and only planned for it after design stage.....

not exactly a good starting point.

Like any mechanical system, there are good ones and bad ones.Risks involved can be minimised by good design and pre planning prior to installation.

baby fish

sydthebeat wrote: »

so you installed yours in a cold attic and only planned for it after design stage.....

not exactly a good starting point.

Like any mechanical system, there are good ones and bad ones.Risks involved can be minimised by good design and pre planning prior to installation.

I agree 100%, it could be a good thing but I've no confidence in it anyway from my experience.


So would you agree then without prior planning it is not suitable for every house? Bet you most installers wont agree

But how can this idea of MHRV creating the perfect indoor air quality be guaranteed? Even in a perfectly designed system. All they seem to be concerned about efficiency and heating bills.

MicktheMan

baby fish wrote: »

So at the end of the day, we don't know how good the IAQ is. Is this not a bit worrying? it was for me. There is a belief it creates the perfect indoor air quality, I'm not so sure. There seems to be no evidence. I suppose you either trust it or you don't.

I'm curious. What iaq parameter data are you looking for?

galwaytt

baby fish wrote: »

Mine wasn't, I decided on ventilation method after design stage was finished.



I can only talk about ducts in the attic, 25mm of insulation is not enough




I would sayit could be a good thing, prove it to me first though



So at the end of the day, we don't know how good the IAQ is. Is this not a bit worrying? it was for me. There is a belief it creates the perfect indoor air quality, I'm not so sure. There seems to be no evidence. I suppose you either trust it or you don't.

Who has this belief ? And where is the evidence that the opposite is better - or indeed worse ??

You're making a lot of assumptions there tbh.

baby fish

galwaytt wrote: »

Who has this belief ? And where is the evidence that the opposite is better - or indeed worse ??

You're making a lot of assumptions there tbh.

Well a number of MHRV units are sold with the following benefits:
"Clean filtered air"

"constant supply of fresh air"

"removing dust and pollen, also provides a superior indoor air quality"

Then I think its fair to say that anyone who has installed MHRV should at least expect it , but as there is no way to regularly monitor the IAQ then how do you know you are actually getting it? This is probably more relevant when a house hasn't been designed with MHRV in mind, indeed the quality of the IAQ of any house should be considered when the method of ventilation has not been decided until the blocks are going up.

I have no evidence that the alternatives are better, or worse, but I do know the air supply has not passed through a longer length of ducting before it enters a room. So I would consider the alternatives to MHRV actually a cleaner source of air, this my opinion only.

Re test: are independent test carried out to prove that the supply and extract do not mix in the unit, I know it shouldn't , but are they actually tested for this? I haven't come across any results, even a simple pass/fail test result.

The MHRV unit I have/had (in process of getting rid of it) I would now consider a budget version, at the time of purchase I thought it was suitable, I suppose it ventilated to an acceptable standard and reduced the heating bill, but I was never confident of IAQ with it - based on a thorough inspection of build quality. It also had no intelligent feedback of what was going on.


If anyone has data on what interior Relative Humidity can be expected with MHRV, maybe an average per month for the house ( excluding wet rooms)
I'd be interested to know what it can acheive

hexosan

So all your problems seem to be based off the fact you didn't get a system that was adequately designed to meet your needs,
-by your own admission you purchased a budget unit (possibly substandard)
- the ducts were insufficiently insulated and placed in a cold attic space.

So taking all this into consideration you've come to the conclusion that. MVhR isn't to be trusted. ??

893bet

If laying attic insulation over the ducts is this adequate in terms of insulation? Or should the ducts run above the attic insulation and be insulated on their own?

MicktheMan

baby fish wrote: »

If anyone has data on what interior Relative Humidity can be expected with MHRV, maybe an average per month for the house ( excluding wet rooms)
I'd be interested to know what it can acheive

So its RH data your interested in.

Below is a snapshot of my 1970's built house with retrofitted mvhr 6 years ago. Duct runs / mvhr unit are in the cold attic (bungalow). Ducts are very well insulated though.

Reason for installation was specifically to reduce the RH (it wouldn't have been unusual to find leather shoes not used in a couple months to be covered in mould). Before installation the salt sellar needed rice to keep salt dry. Within 24 hours of commissioning, salt was dry without rice. No mould since.

Prior to mvhr installation, various methods of natural ventilation were tried but failed.



Note that this is data from a 40 year old but reasonably air tight house but with significant thermal bridging / insulation issues compared to a well built newer house. Therefore, I would expect RH data from a well built newer house to be better.

Also note that for any ventilation system to work wrt controlling RH, the house needs to be adequately heated too.

TaraGreene

im not an expert on this matter however i do believe that MVHR is an easy solution to heating and ventilation but the air quality can never be the same as using natural ventilation

ferryman35

Is it not correct to say that all any ventilation system is moving the air from one place to the next. So neither an MHRV system nor natural ventilation system will add anything and take very little away?

All an inlet filter will remove are particulate contaminants that would only finish up somewhere as dust but the air isn't treated in any way. The heating process in an MHRV is indirect so it in itself doesn't contaminate the air with anything but just helps with rh?

Where problems could arise is where 'possible contaminants' are introduced wherever that air is used, eg. inside the house.

From what I see, natural ventilation is very subject to the prevailing atmospheric conditions, so if there is no air movement outside, there will be very little moving in & out of the house. Likewise, if its very windy, you'll have lots of air movement. Question is will you want it when you get it?

My one question with MHRV is that within the house air has to circulate from the inlet vents to the extraction vents, and I wonder about what happens in between. Standard systems seem to be configured such that air is introduced to the Living & bedrooms & extracted through the kitchens & bathrooms - I am seriously considering specifying our system so that the fresh air is introduced to the hall, landing & living room & extracted through the bedrooms as well as the bathrooms & kitchens. In the mornings there is a considerable amount of condensation on our bedroom windows. I also think for the few times that there might be someone bed sick that it would be better that their exhaled air would be extracted straight out rather than circulate to another room before it got extracted. With a filtered extraction port in the Kitchen I can't see how this configuration of MHRV could be beaten to be honest

BryanF

TaraGreene wrote: »

im not an expert on this matter however i do believe that MVHR is an easy solution to heating and ventilation but the air quality can never be the same as using natural ventilation

Never?

BryanF

MicktheMan wrote: »

So its RH data your interested in.

Below is a snapshot of my 1970's built house with retrofitted mvhr 6 years ago. Duct runs / mvhr unit are in the cold attic (bungalow). Ducts are very well insulated though.

Reason for installation was specifically to reduce the RH (it wouldn't have been unusual to find leather shoes not used in a couple months to be covered in mould). Before installation the salt sellar needed rice to keep salt dry. Within 24 hours of commissioning, salt was dry without rice. No mould since.

Prior to mvhr installation, various methods of natural ventilation were tried but failed.



Note that this is data from a 40 year old but reasonably air tight house but with significant thermal bridging / insulation issues compared to a well built newer house. Therefore, I would expect RH data from a well built newer house to be better.

Also note that for any ventilation system to work wrt controlling RH, the house needs to be adequately heated too.

You can tell when Mick had takeaway

sydthebeat

TaraGreene wrote: »

im not an expert on this matter however i do believe that MVHR is an easy solution to heating and ventilation but the air quality can never be the same as using natural ventilation

You need to do more home work.

baby fish

hexosan wrote: »

So all your problems seem to be based off the fact you didn't get a system that was adequately designed to meet your needs,
-by your own admission you purchased a budget unit (possibly substandard)
- the ducts were insufficiently insulated and placed in a cold attic space.

So taking all this into consideration you've come to the conclusion that. MVhR isn't to be trusted. ??

I've no problem admitting the mistakes I made, that's why I'm stating them in this thread, hopefully others wont do the same. Yes, ventilation should be considered during design stage. Even if it was...

I didn't buy a budget version, its from a well known manufacture, it was advertised as doing all the usual stuff you'd expect a MHRV, their best model, its only now after looking at it closely I would consider it substandard.

But that's my point, what min standards are in place for build quality of a MHRV unit? - None as far as I can see.

If one bad design can make its way into a home, no reason why others can too. That's why I don't trust it

baby fish

MicktheMan wrote: »

So its RH data your interested in.

Below is a snapshot of my 1970's built house with retrofitted mvhr 6 years ago. Duct runs / mvhr unit are in the cold attic (bungalow). Ducts are very well insulated though.

Reason for installation was specifically to reduce the RH (it wouldn't have been unusual to find leather shoes not used in a couple months to be covered in mould). Before installation the salt sellar needed rice to keep salt dry. Within 24 hours of commissioning, salt was dry without rice. No mould since.

Prior to mvhr installation, various methods of natural ventilation were tried but failed.


Note that this is data from a 40 year old but reasonably air tight house but with significant thermal bridging / insulation issues compared to a well built newer house. Therefore, I would expect RH data from a well built newer house to be better.

Also note that for any ventilation system to work wrt controlling RH, the house needs to be adequately heated too.

Yes I would expect it to be better in a sealed house too, I'm currently getting around 50% using temporary natural ventilation. I've opened a few windows to the trickle position. As to how efficient natural ventilation is, that all depends on house orientation , foot print, room layout, position of vents, under cut of doors, use of extractor fans, cross ventilation etc. It needs to be planned as much as hrv needs to be for it to be effective

Thanks for your data, anybody got some for a sealed house?

baby fish

TaraGreene wrote: »

im not an expert on this matter however i do believe that MVHR is an easy solution to heating and ventilation but the air quality can never be the same as using natural ventilation

I think the point is if you want Fresh air, get it through the shortest possible duct i.e.straight through the wall 350mm wall vent. It will be More expensive to heat your house but you will have outside fresh air

If you are happy with filtered air that has passed through ducts and a lower heating bill go with MHRV
But the cost of electricity and filters for has to be factored in too

My preference is now to have fresh air even if that means a higher heating bill

MicktheMan

baby fish wrote: »

Thanks for your data, anybody got some for a sealed house?

Define "sealed"

baby fish

ferryman35 wrote: »

I am seriously considering specifying our system so that the fresh air is introduced to the hall, landing & living room & extracted through the bedrooms as well as the bathrooms & kitchens. In the mornings there is a considerable amount of condensation on our bedroom windows. I also think for the few times that there might be someone bed sick that it would be better that their exhaled air would be extracted straight out rather than circulate to another room before it got extracted. With a filtered extraction port in the Kitchen I can't see how this configuration of MHRV could be beaten to be honest

With Mhrv, the system has to be balanced, you cant have more exhaust than supply. its usually the other way, more supply than exhaust.

if its a retrofit, have you considered DCV? less ducts and no filter changes and cheaper to run (No heat exchanger though).
They use humidity sensitive air inlet vents with an airflow controller so this might go some way to reduce unwanted draughts

baby fish

MicktheMan wrote: »

Define "sealed"

You know what I mean! what is usually referred to as airtight . All measures taken to make it as airtight as possible

sydthebeat

baby fish wrote: »

I think the point is if you want Fresh air, get it through the shortest possible duct i.e.straight through the wall 350mm wall vent. It will be More expensive to heat your house but you will have outside fresh air

If you are happy with filtered air that has passed through ducts and a lower heating bill go with MHRV
But the cost of electricity and filters for has to be factored in too

My preference is now to have fresh air even if that means a higher heating bill

Your science is a bit misguided.

pressure from external air movement in a naturally ventilated house will mean that generally one side of the house is "inlet"ing and one side is "outlet"ing.
This means that the internal air is being pushed around the home from one side to another, much in the same manner as mhrv.
The difference being that with mhrv The effects are gently more centralised resulting in less area for air to move in.

Natural ventilation is absolutely No guarantee of any better indoor air quality than mhrv.
Like any mechanical system mhrv must be planned, designed, installed and maintained properly.

A properly working mhrv system would, in my opinion, lead to a much better IAQ than natural ventilation because of the homogenous nature of the air quality and relative humidity.

MicktheMan

baby fish wrote: »

You know what I mean!

I don't and that's why I asked.

For mvhr to be any way effective (especially the hr bit), the actual air tightness (measured) is quite important.

hexosan

sydthebeat wrote: »

Your science is a bit

a BIT

baby fish

sydthebeat wrote: »

Natural ventilation is absolutely No guarantee of any better indoor air quality than mhrv.

I don't think I said it would guarantee an overall better IAQ, I just gave my opinion that at the point of entry into a room, natural ventilation supplies fresh air while MHRV supplies filtered air(that has travelled a longer distance through an AHU and ducting, these areas could be locations where deterioration of air quality can occur if little effort has gone in to the design of the AHU, if there is not proper sealing/separation within the AHU of supply and exhaust airways , if the AHU and ducting are not maintained or if the ducting has been badly installed/insulated.

I questioned the quality of MHRV IAQ , not because of MHRV's ability to create a sufficient flow of air through a house and reduce RH, but because I cant confirm that there are any tests carried out re airtightness of the AHU/isolation of supply and extract within the AHU and also because IAQ is not tested after installation, its just accepted as being of healthy IAQ . RH is only one aspect of IAQ, I'm more concerned with e.g. mould spores entering from ducts.

sydthebeat wrote: »

A properly working mhrv system would, in my opinion, lead to a much better IAQ than natural ventilation because of the homogenous nature of the air quality and relative humidity.

In theory yes, but reality is there is no way knowing for sure that a particular installation is working properly.

In my opinion, natural ventilation provides fresher air and if its is not ventilating properly (high RH) then a DCV fan should be introduced.

baby fish

hexosan wrote: »

a BIT

No need to shout,

could you expand on your thought?

baby fish

MicktheMan wrote: »

I don't and that's why I asked.

For mvhr to be any way effective (especially the hr bit), the actual air tightness (measured) is quite important.

Apologies, I could have phrased it better, thank you for your RH graph.

sydthebeat

baby fish wrote: »

In my opinion, natural ventilation provides fresher air and if its is not ventilating properly (high RH) then a DCV fan should be introduced.

In my opinion, your opinion is baseless.

A comfortable RH measure is between 65 and 75%. DCV will only every react to that level, and cannot enforce that level.
Plus dcv does not have heat recovery.

Your points are valid, but are based on a system not working
There is just as much risk when a natural system doesn't work.

baby fish

sydthebeat wrote: »

In my opinion, your opinion is baseless.

that's fair enough

Its an opinion based on the design/installation of the ducting in my house and also from inspection (by me) of the design/assembly of the AHU in my house.

Its based on what I've seen in front of me, some will consider my opinion pointless, it will give others something to think about and question.

sydthebeat wrote: »

A comfortable RH measure is between 65 and 75%..

I would consider a suitable RH of 40% - 65%, I would definitely expect the normal RH to be under 65% in a house with MHRV, I think I would expect 40% - 55% really. obviously peaking up around 70% during cooking/showers etc. I could be wrong , but that's what I'd expect.

Has anybody got a graph/data for a well insulated house with an air permeability that allows the MHRV to run at its optimum? A graph like mick has would be useful.

sydthebeat wrote: »

DCV will only every react to that level, and cannot enforce that level. .

It should react to all levels of RH humidity, min extract and supply ventilation rate is set for RH of 40% (I think) and max extract/supply will be at 70% RH (I think) . The inlets/outlets should be humidity sensitive and will adjust to the RH of their location while the fan is wired to the extract points and will increase/decrease its speed according to measured RH at these points in the wet areas.

sydthebeat wrote: »

Plus dcv does not have heat recovery. .

This is a disadvantage when compared to MHRV but there are advantages to offset this, lower running costs and no filters to purchase annually. There are other Adv/disadv to both

sydthebeat wrote: »

Your points are valid, but are based on a system not working .

Your points are equally valid but based on a system that works

sydthebeat wrote: »

There is just as much risk when a natural system doesn't work.

agreed, there are risks with every ventilation when not designed and installed properly.


Think of it this way, in Europe we use EURO NCAP to test car safety. It gives consumers and manufacturers an independent and realistic assessment of car safety. Without it (and similar testing around world) where would car safety be? Who knows, some manufacturers will design safe cars, some will try, some wont. But They will all claim their car is safe to drive, but would it be?? How would you know until it crashes or there has been a number of crashes ?

Regarding MHRV, in particular to IAQ and more importantly the supply of clean air, this was asked in post 1, but maybe not so clearly:
1. what independent tests are in place to ensure that there is no mixing of exhaust/supply within the sealed shell of the AHU?
2. What results are available
3. If tested what is a pass/fail (what % of leakage is allowed if any)

That's what I want to know and that's the point of this thread. Its either tested or its not.
if its not tested then its a self regulating industry and this should be something to consider if planning to install MHRV,
if it is tested then a homeowner should be able to install MHRV knowing that the air from the AHU is clean at the point of entry into the ducts, and if the ducts are well designed and installed , then the air should be clean at the point of entry into a room .

baby fish

baby fish wrote: »

that's fair enough

Regarding MHRV, in particular to IAQ and more importantly the supply of clean air, this was asked in post 1, but maybe not so clearly:
1. what independent tests are in place to ensure that there is no mixing of exhaust/supply within the sealed shell of the AHU?
2. What results are available
3. If tested what is a pass/fail (what % of leakage is allowed if any)

.

I will take it is not tested so....

sydthebeat

baby fish wrote: »

I will take it is not tested so....

google is your friend

baby fish

Thanks for this Syd but the scope of this test seems to suggest that the purpose of the test is to determine if the unit can supply/extract air at a rate that will satisfy building regs part F and also to determine the average electrical input to the fan, I can't see anything to do with checking for air leakage within the unit to ensure there is no mixing of the supply and extract

"The object of this test method is to assess the ability of a ventilation package to provide the continuous supply and extract (trickle) air flow rates required by the Building Regulations Approved Document F (Ventilation). The method also allows the effective power input to the fan to be determined at this flow rate at each operating point when the system is installed in accordance with the manufacturer’s instructions".

Except for this which seems to suggest that up to 5% leakage is allowed

The leakage classification shall be Class 2 or better i.e. 5% internal and external leakage or less. If the unit fails to meet class 2 or better, the aerodynamic air flow rate and thermal tests shall not be undertaken.

iriray

sydthebeat wrote: »

A comfortable RH measure is between 65 and 75%.

The studies usually show that comfortable and healthy RH measure is usually between 30-50 % RH. If it's usually that high as you say, it is no wonder that many homes in Ireland suffer mold and mildew that leads to low indoor air quality and health hazards.

sydthebeat

iriray wrote: »

The studies usually show that comfortable and healthy RH measure is usually between 30-50 % RH. If it's usually that high as you say, it is no wonder that many homes in Ireland suffer mold and mildew that leads to low indoor air quality and health hazards.

i was working from memory on that one, no problem saying im incorrect.

most statements i can find on line put optimal humidity at 40 - 60%

see conclusion page 358

Andrew_Doran

sydthebeat wrote: »

most statements i can find on line put optimal humidity at 40 - 60%

see conclusion page 358

Here's another version of that chart:

iriray

Btw, are there any studies about Indoor Air Quality made in Ireland available? Does anyone know?