HUMIDITY LEVELS IN THE HOME

jenningso · 30-09-2011 1:07pm #1

Hi, does anybody know what Relative Humidity setting to leave a HRV system at? With outdoor humidity in Ireland ranging from 70-100%, surely it can't be feasible to achieve the 30-50% RH recommended by most. HRV systems aren't de-humidifiers! I've never really read much into humidity until now, so what do most Irish people do in their own homes? Should we all have de-humidifiers to prevent mould and dust mites etc??

BryanF · 30-09-2011 1:41pm

jenningso wrote: »

Hi, does anybody know what Relative Humidity setting to leave a HRV system at? With outdoor humidity in Ireland ranging from 70-100%, surely it can't be feasible to achieve the 30-50% RH recommended by most. HRV systems aren't de-humidifiers! I've never really read much into humidity until now, so what do most Irish people do in their own homes? Should we all have de-humidifiers to prevent mould and dust mites etc??

is this a new house? as in is it still drying out? are you having problems with mould or surface condensation or is this pre-emptive? I would presume that the RH will reduce during the heating season.. what Rh setting options have you got? why not just play around with it to see what suits you..

jenningso · 30-09-2011 2:01pm

Yeah, it's a new house alright. It's just that I've noticed throughout the summer that indoor humidity levels pretty much track outdoor humidity (allowing for temperature difference and weather). The house is dried out for sure but do Irish houses get humidity levels down to the 30-50% level recommened? Is it worth getting a de-humidifier? I get chest infections pretty often, so wondering aloud now about humidity (even though I haven't had any illness since moving into the new house 4 months ago).

MicktheMan · 30-09-2011 2:21pm

jenningso wrote: »

Hi, does anybody know what Relative Humidity setting to leave a HRV system at? With outdoor humidity in Ireland ranging from 70-100%, surely it can't be feasible to achieve the 30-50% RH recommended by most. HRV systems aren't de-humidifiers! I've never really read much into humidity until now, so what do most Irish people do in their own homes? Should we all have de-humidifiers to prevent mould and dust mites etc??

The following assumes a proper functioning ventilation system is present or ventilation strategy is employed:
Internal RH% of 40-50% during the heating system is easily possible. The level of RH% achieved is a function of moisture generation with the home but also is dependent on the outside air temperature. The colder it is outside the lower the internal RH% can be.
Outside the heating period (apr-sep) the RH% inside can go as high as 80+% because of minimal temperature difference betwween inside & outside.
(I have a mvhr system and have monitored this very phenomenon over last winter. I will try to attach an image of the RH% over a period of time below. You will see that the RH% is high at the beginning and end of the period monitored. This corresponds to the relatively milder weather before and after last years cold snap leading up to christmas)

Now to your question. On your MVHR system there should be a condensation drain coming from the heat exchanger which carries the condensate away (as the warm internal air cools to below the dew point, the moisture condenses). It is through this process that the moisture is expelled from the house. This process ceases as the outside air temp increases in the warmer months.

jenningso · 30-09-2011 2:36pm

Wow, thanks for the very detailed reply Mick. That's exactly what I was looking for. I know about the condensation drain from the HRV and I've seen it drip after showers/baths etc. I just changed the setting today down to a desired humidy level of 60% (what have you set yours at, I'd guess 50%, right?) and I look forward to see the results once the heating season begins (installing a stove soon). I've hygrometers upstairs and downstairs and the built-in hygrometer in the HRV itself. It's great to see somebody has studied this phenomenon as there is very little irish info online. Have you noticed less colds/flus in your house now that you get RH down to 40/50%? Thanks again Mick.

MicktheMan · 30-09-2011 2:49pm

Hi jenningso,
the control of our system is a lot simpler than yours I guess as there is no humidity control on the unit. We have a high,low & boost setting.
We run it on low normally but during short periods of high activity (friends over for party etc) we would put it to high. We also have boost switches at the doors of the bathroom and in the utility which we hit when showering etc (system goes into high mode for 20 mins after which it returns to low).
In my mind, using RH% to control a mvhr system doesn't make a whole lot of sense as the external conditions have such a large impact on internal RH% levels as explained in my previous post and can be seen in the data.

In any case, glad to be of help and yea very few colds etc

jenningso · 30-09-2011 3:01pm

Yeah, I was thinking that the humidity setting would be of little use because the outside air could be as humid as 100%. My hrv has a humidity sensor and a co2 sensor, so on auto it strives to match my desired settings. I'm going to monitor it over the winter to see if setting a lower desired RH% makes any difference. No point the system boosting trying to remove humidity when the air it's taking in is even more humid!

Cheers, Owen

creedp · 30-09-2011 3:09pm

MicktheMan wrote: »

Hi jenningso,
the control of our system is a lot simpler than yours I guess as there is no humidity control on the unit. We have a high,low & boost setting.
We run it on low normally but during short periods of high activity (friends over for party etc) we would put it to high. We also have boost switches at the doors of the bathroom and in the utility which we hit when showering etc (system goes into high mode for 20 mins after which it returns to low).
In my mind, using RH% to control a mvhr system doesn't make a whole lot of sense as the external conditions have such a large impact on internal RH% levels as explained in my previous post and can be seen in the data.

I'm glad you said that as I also have a MRHV system that doesn't have a built in hygrometer or hygrometers placed around the house and I thought to myself I must have installed the mother of all dinosaur units!!. Nor do I measure the Rel humidity of the house and adjust the unit accordingly. Like your unit I have a high/medium/low setting with boost buttons and I leave it on low and let it get on with its business. Of course the Q can be asked how do I know its doing its job correctly? My condensate drain is connected into the overfloow for the DHW cylinder and plumbed outside - should I notice a constant drip from this, especially in cold weather? How else do I monitor the ongoing effectiveness of the unit? Must ask the installer these very Q's but wondering if you have any views?

MicktheMan · 30-09-2011 4:33pm

creedp wrote: »

Of course the Q can be asked how do I know its doing its job correctly? My condensate drain is connected into the overfloow for the DHW cylinder and plumbed outside - should I notice a constant drip from this, especially in cold weather? How else do I monitor the ongoing effectiveness of the unit? Must ask the installer these very Q's but wondering if you have any views?

The following simple checks can be done when it is cold outside and heating is on inside.
As you say, check that the condensate drain is dripping water. This shows that heat exchange is happening as the internal air cools it dumps its moisture.
Feel the temperature at the inlet vents. It should be close to the extract temperature less 1 to 1.5 degrees.
The installation company should also be able to check the system using a calibrated thermometer/anemometer.
Also don't forget to regularly clean/replace the air filters.
Another (high tech;)) check is to check the saltsellar. If the salt is dry then so is the air:).

creedp · 03-10-2011 9:39am

MicktheMan wrote: »

The following simple checks can be done when it is cold outside and heating is on inside.
As you say, check that the condensate drain is dripping water. This shows that heat exchange is happening as the internal air cools it dumps its moisture.
Feel the temperature at the inlet vents. It should be close to the extract temperature less 1 to 1.5 degrees.
The installation company should also be able to check the system using a calibrated thermometer/anemometer.
Also don't forget to regularly clean/replace the air filters.
Another (high tech;)) check is to check the saltsellar. If the salt is dry then so is the air:).

Thanks for that ... these are the criteria that even I can understand:) When you say check the inlet air temp are you using a thermometer or simply using your own intuition?

MicktheMan · 03-10-2011 12:51pm

creedp wrote: »

When you say check the inlet air temp are you using a thermometer or simply using your own intuition?

I use a calibrated thermometer (as I use this equipment in my day to day business).

creedp · 03-10-2011 1:05pm

MicktheMan wrote: »

I use a calibrated thermometer (as I use this equipment in my day to day business).

Thanks Mick. The installer is due back for a once over shortly and must ask him to test the temp of the inlet air to see what happens.

L driver · 19-11-2012 2:39pm

Hello,
Sorry for digging out an old thread, but if the rh outside is 70%+ as it is these days how can it be reduced without a dehumidifiier??

BryanF · 19-11-2012 5:07pm

Heat

L driver · 19-11-2012 9:02pm

more heat and then the humidity rises again.

peterc14 · 20-11-2012 2:07pm

Would be interested to know what humidity levels people are gettin in their houses.

I am in a new house and the humidity is almost always 60 - 70%... is this normal?

MicktheMan · 20-11-2012 10:00pm

L driver wrote: »

Hello,
Sorry for digging out an old thread, but if the rh outside is 70%+ as it is these days how can it be reduced without a dehumidifiier??

Don't think you can reduce the rh of the outside air:D

However, external air at 5 degC and 70% rh will contain a fraction of the moisture compared to internal air at 20 degC and 70%rh. This is true even if the external air is 90% rh.

MicktheMan · 20-11-2012 10:03pm

peterc14 wrote: »

Would be interested to know what humidity levels people are gettin in their houses.

I am in a new house and the humidity is almost always 60 - 70%... is this normal?

Depends on external conditions. the colder it is outside the lower the rh should be inside. 60 - 70% is normal in mild conditions but too high during cold weather. Anything above 70% prolonged over time and you're in the high mould risk spectrum.

L driver · 20-11-2012 10:16pm

MicktheMan wrote: »

Don't think you can reduce the rh of the outside air:D

However, external air at 5 degC and 70% rh will contain a fraction of the moisture compared to internal air at 20 degC and 70%rh. This is true even if the external air is 90% rh.

Of course!! The penny drops. Would a new build be more prone to high rh in the first year of occupancy?

BryanF · 20-11-2012 10:19pm

L driver wrote: »

Of course!! The penny drops. Would a new build be more prone to high rh in the first year of occupancy?

add heat and ventilation! and relax the house is just drying out

root69 · 07-12-2015 10:55am

Hi,
was thinking if to open new thread or just revive his one.. This is exactly the topic I am looking for and the user comments I would expect so I will revive this by posting here...

:::Details:::

Newly build house being habited from a year and half. House is label as BER A3. South facing garden.
The RH% indoors varies from room to room. Living room is in avg. between 60-70%. Kitchen 55-70%. Temperature is between 16-20C. Avg at 18C. Heating runs 40min once a day.

For the values above, normally the outdoor environment is at RH% 78-90% with 9-14C.
If the outdoor temperature drops the indoors RH% will also drop but never registered below 50%

There is no RH system as previously mentioned. Only the normal central heating, which I believe if different than what you mentioning with HR systems.

The windows vents are open and windows are open often. I noticed that indoor RH% increases when windows are open... perhaps the humidity coming in.. if this makes sense...

Few questions...:

Are these values normal or it with time if these remain it might attract problems? Is action required, in your opinion?
Is it the case that the building is still drying out? If yes, for how long (in avg) would a building dry out?
Should the vents be kept open? heating for longer? what is your recommendation.

thank you

galwaytt · 07-12-2015 11:37am

....well, looking at the temp/RH meter on the wall of my office now (same spec build as a house) on this post Storm Desmond morning, I'm looking at 19 Deg C, 40%Rh. No heat on, MHRV humming away and the window open a smidge.

root69 · 07-12-2015 11:40am

galwaytt wrote: »

....well, looking at the temp/RH meter on the wall of my office now (same spec build as a house) on this post Storm Desmond morning, I'm looking at 19 Deg C, 40%Rh. No heat on, MHRV humming away and the window open a smidge.

thanks.
Is these MHRV a noisy thing? Would you have it at home?

galwaytt · 08-12-2015 9:47pm

root69 wrote: »

thanks.
Is these MHRV a noisy thing? Would you have it at home?

I have it in both. Can't hear it at home at all. - you're not supposed to anyway. I can't see a way of modern building without it tbh..

WexfordRonald · 17-09-2020 4:21pm

Hello, I moved into a house last year(built 1998).within the first month we noticed specks of mould at the top of walls which we wiped away. However my daughter quickly started snoring at night and I had blocked sinus for 2 months. We bought 2 dehumidifiers which told us the rh level in the back part of the house is 95%.All the rooms have vents and I recently installed an envirovent in the bathroom. I also got the walls pumped last week with insulation but still seeing no different in the rh measurements. Very concerned going into winter as I don't want my daughter to become sick. The house is south facing which seems to be part of the issue. Any help would be appreciated

MicktheMan · 17-09-2020 5:45pm

WexfordRonald wrote: »

Hello, I moved into a house last year(built 1998).within the first month we noticed specks of mould at the top of walls which we wiped away. However my daughter quickly started snoring at night and I had blocked sinus for 2 months. We bought 2 dehumidifiers which told us the rh level in the back part of the house is 95%.All the rooms have vents and I recently installed an envirovent in the bathroom. I also got the walls pumped last week with insulation but still seeing no different in the rh measurements. Very concerned going into winter as I don't want my daughter to become sick. The house is south facing which seems to be part of the issue. Any help would be appreciated

First off, there is rarely a single silver bullet solution to these types of issues and many people have made changes to try to solve the problem but in fact make the situation worse inadvertently. Getting educated on the physics of what is happening in your best bet at this stage. Without basic knowledge you could be chasing your tail for years.

Answering the following q's with as much information as possible (and pictures of affected areas) may help identify the issues at play, though you may still need to have the house properly surveyed:
1. When did you move into your house and what months of the year do you see the issue?
2. How is house heated; does it heat up; do you use the heating?
3. How many in your household?
4. What are you using to get the 95% rh reading and what temperature was the room?
5. Are there any active water leaks in the house (e.g. roof, pipework)?
6. Was the house lived in before you moved in or was it left vacant for a period?

Imo, one of two things is going on here; either you have a significant problem in your house or you have misinterpreted some important pieces of information.
For instance, having 95% relative humidity on a continual basis in your house is extreme and would be very rare in a domestic setting.

WexfordRonald · 17-09-2020 7:36pm

Hi Mick,
Thanks for replying. Will try and give as much details as I have.
1. I moved in at the end of Oct last year, the house had been used as a summer house previously. After almost 3 weeks we starting to notice spots of mould on my daughters wall
2.we have a normal oil heating with radiators in all the bedrooms. Have it running for an hour in the morning and evening during winter.
3.there are 3 of us in total. Also since my wife started working from home in our bedroom, the walls there have gotten very bad with small green spots spreading all over
4. I got the rh reading off the dehumidifier. When I turn it on it usually starts at 85 and then goes up to 95% after a few seconds.
5. No active leaks. Most of the mould appears at the top of the walls. I had the house surveyed by 2 different people and they haven't noticed anything odd. Vents are open etc. If u need some photos I can attach tomorrow. Thanks

MicktheMan · 17-09-2020 8:34pm

Yeah, put up the pictures of the affected areas.
Based on what you've said, what might be happening is something as follows:
House was a summer house so heat retention is poor (not just poor insulation either) to begin with. Add on top of this possible insufficient heating schedule. This underheating will then reduce the efficiency of whatever ventilation system / strategy is employed leading to excess water vapour internally which is condensing on any and everything inside close to or below the dew point temperature of the internal air especially in the cooler areas of the house. This (relatively constant) condensation is then the moisture source for the mould to thrive.

WexfordRonald · 18-09-2020 9:23am

Hi Mick,

Have attached the photos now, this is from the spare room but it is the same in my bedroom and my daughters but i have wiped it away best i can. Would you be able to provide any solutions? as mentioned, i had the walls pumped last week and the environvent installed in the bathroom which i hope will help with the air flow. However i am still seeing condensation on the window in the morning even with the dehumidifier on all night.

Thanks

MicktheMan · 18-09-2020 2:50pm

Thanks for the photos.
Having condensation on the windows in the morning at this time of year is not unusual in that houses get "wet" during the warmer months and then dry out at the start of the cooler months and the condensation you are seeing may be just a manifestation of this drying process. However, the level on condensation seen should continually decrease to nothing over a number of weeks.
If this doesn't happen, then you still have some issues to address. What the issues are exactly and how best to address them cannot be accurately determined without a proper on-site survey which should include a period of monitoring of internal conditions.

LostAgain13 · 16-01-2021 11:39pm

Hi, what sort of temperature/humidity should a holiday home in Ireland be kept at? Or would anyone know where that information might be available. I could see where temperature might be a set value year round, but the humidity might be a moving target based on outside conditions. Any information out there?

Thanks.

HUMIDITY LEVELS IN THE HOME

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