Most of your mould issues can be solved by just opening your bloody windows for 5 minutes every once in a while. Especially when it's cold. Every other country in Europe does this. Here people look at you as if you're insane for suggesting it.
If you’ve got an ice cold (dry) winter day: good.
Average UK or Irish winter day is wet/sleety cold: you’re just introducing more humidity into your home
One problem with that: warmer air can hold more humidity than colder air . At 0 °C the max moisture is 4.89 g m^-3; at 20 °C it's 17.3 g m ^-3.
So it doesn't matter if it's raining outside, you're still likely to reduce airbourne moisture by leaving the window open.
That’s my point: it’s milder in Ireland and UK (but still cold) in winter. Opening the windows in Germany at -5°C might make sense, but doing so in Ireland at +5°C will bring humidity into your home
It still works, even if the +5degC air is at 100%RH, bringing it in and heating it even to 15degC reduces the RH to just over 50%.
Feb 4, 2026 11:48RH is about 80-90% in Ireland in winter- almost constantly damp and average daytime highs are about 7°C
If you take air at 7degC, 90%RH and heat it up to 15degC without adding or subtracting any moisture to it, the RH drops to about 53%
Once you get to an outside temperature of about 12-15degC, it stops working. But at 5-7 it still works.
