Hi all. I'm looking for some advice for high relative humidity throughout my house in the colder / rainy seasons - which I observed last year and again in the last few weeks (as it gets colder and rainier). I have a hygrometer installed downstairs (in the kitchen) and upstairs (in the bathroom) and these are the general readings I get:
Relative humidity in warmer / drier seasons:Downstairs (Kitchen) - usually 40% to 50% -
max 55%Upstairs (Bathroom) - usually 40% to 55% -
max 60%Relative humidity in colder / rainy seasons:Downstairs (Kitchen) - usually 55% to 65% -
max 77%Upstairs (Bathroom) - usually 55% to 75% -
max 86%Some other notes:
- I try to curb excess humidity by opening windows during the day to increase ventilation, but this can have the opposite effect if it's cold or wet outside.
- On very cold nights I get a lot of condensation on the aluminium window frames in the bedroom overnight, which I have to mop up with a rag in the morning. Windows are double glazed.
- I have split system ACs throughout the house, but I barely use them (unless it's very hot) to keep costs down.
- The only instances of mould I've found throughout the house (in 3 years) were in the split system ACs - I had them professionally cleaned a year ago and mould hasn't come back.
The advice I'm after is: what is causing the high relative indoor humidity when its cold/wet? Is it dangerous? And what can I do to manage it?
Thanks.
it could be due to people breathing in a house that's completely locked down.
we generally run the ducted aircon in dehumidifier mode, even during summer. while it doesn't bring down the temperature as much as cooling mode does, it makes it more tolerable due to reduced humidity, and it consumes less power.
so i'd check if your aircon has that mode, and whether the cost of running it in that mode is acceptable to you
The numbers don't seem silly high - how does it compare to the published humidity?
How does ambient compare to dew point in the rooms?
People lose a lot of water through normal activity
I use these in our ensuite (which is connected to the WIR) and drying room (spare bedroom that has the clothes airers) and haven’t had any issues with dampness or mould:
https://www.bunnings.com.au/damprid-han ... k_p4470243
Also we use the set mode for air con too - is heaps more comfortable and uses 30% less power according to manufacturer
Thanks for the replies.
i'd check if your aircon has that mode, and whether the cost of running it in that mode is acceptable to you
My split systems have a 'dry' mode, but I'm apprehensive to run them 24/7 because of the cost. I suppose I can run it on the particularly rainy days.
The numbers don't seem silly high - how does it compare to the published humidity?
How does ambient compare to dew point in the rooms?
Currently where I am, (outdoor) it's rainy, 16 degrees and 79% relative humidity.
In the upstairs bathroom (indoor), it's 20 degrees and 64% relative humidity.
I've always thought it was reasonable that the humidity indoors would be anchored to the outdoor humidity to some extent. But googling around, I see nothing but "keep indoor humidity below 60% or you'll get mould or worse".
the humidity indoors would only be anchored to outdoors if you let the air circulate between the two.
i'd check how much electricity the 'dry' mode on your aircon is using. it may be not as much as you think, since it doesn't need to cool the air as much. it only needs the coils to be cold enough for condensation to happen.
How long is the humidity high for? Or is that the average? I don't think it's terrible but you are obviously getting condensation in the bedrooms so it's bad enough. I'm assuming the window frames aren't thermally broken? Probably why you're getting condensation there. Did you get a vapour permeable weather barrier installed when built? Or was it a vapour barrier? There's such thing as interstitial condensation that happens within the walls where a surface goes below dew point. A good vapour permeable weather barrier will allow moisture in the walls to escape outside. A barrier can mean water condenses within the walls.
First thing would be to make sure your exhaust fans work well and maybe install run-on timers for after showers. Same goes for rangehood. Remove as much moisture from showers and cooking as possible. If you still have high RH, i've heard de-humidifiers work well (as do RCACs).
Good luck
To begin with what happens in Qld. is different as to what happens in Vic.
Qld has higher humidity to begin with whereas Vic is drier
When assessing humidity from area to area you don't compare apples to bananas on the basis that it's all fruit.
Kitchen to bathroom, bathroom will always have a higher moisture content.
Mould requires a degree of heat and moisture to propagate.
Another thing that promotes mould is the use of some 'natural' cleaners and detergents along with types of paint.
The worst time for indoor moisture precipitation is during frost conditions, where there is zero air movement and no alternating pressure between ambient and internal.
Air movement stops precipitation however a house that is warm and tightly sealed during winter is likely to have moisture precipitation on any internal glass or metal surfaces.
Internal air movement, no matter how slight will offset this during frost conditions.
Moisture ingress is likely to occur with an unsarked metal roof.
The expansion and contraction of the internal volume due to thermal temperature.
As the volume inside the house cools it shrinks creating an internal negative value and the house will draw in air from outside to equalise.