How to keep humidity down

ripplyuk

I've noticed that the humidity in my house corresponds to the weather outside. On a bright, dry day, it's usually between 35-45%, but on wet days it rises quickly. We've had a few days of rain and today my humidity monitors are showing 55%, but it has went as high as 68% previously after a lengthy spell of wet weather.

I'm unsure of what to do about this. I'm paranoid about damp (due to a previous rented house) so I'm extremely careful about using extractor fans when bathing or cooking, never drying clothes in the house, opening windows regularly, no pot plants etc. I have the heating on most of the time and the house seems quite well insulated as it takes a while for the temperature to start dropping if the heat is off. I also have trickle vents on all windows and they are open all the time, except a couple of days last year during a storm.

I know the general advice is to open windows to reduce humidity, but when I do that in wet weather, the humidity rises.

Terry98

Have you thought about a dehumidifier?

Plenty of positive posts on here about them.

dominoman

You're worrying over nothing. 68% humidity isn't too bad, especially if it is wet outside.

The humidity outside and inside will always be related. There is enough airflow to make sure of that.

In Summer my house gets down to 40% on occasions, but generally it is around 60 to 65%. The cellar a little higher.

Do you have any damp problems?

cyclonebri1

I agree with Dman, if the humidity varies with the weather it's doing just that. If it stayed high, which is normal in wet weather, and didn't drop when it was dry then you may just have a problem.

Something as simple as a non plated steel washer left on a window cill will give a good indication, it shouldn't rust within the home.

PS, I use a dehumidifier in 1 room during the winter. I have the classic issue of fitted wardrobes on an outside corner wall in a bungalow, ie 4 cold surfaces. Any leather coats or shoes develope mould if I don't do this inspite of leaving the doors open. I've even fitted grills th the kick boards and again in the tops of the units but it still needs the dehumidifier.

Unlike you we keep the heating to a minimum.

I don't think you have an issue

Valli

If you're getting mould and mildew indoors then you have a problem. As has Been said, humidity outside will impact on the level indoors, that's to be expected.

ripplyuk

I didn't realise that this was normal. It's confusing because everything I read says the humidity needs to be below 40%. But it must rise in wet weather in every house.

There's no sign of damp in the house at all. When I first moved in, it had been empty for months, but there was no damp or musty smell. However, during the winter, there would sometimes be a bit of condensation on the bedroom window, first thing in the morning. I've thought about getting a dehumidifier but they're so expensive to run. I don't want to get one unless it's really necessary.

Since the humidity rises if I open windows in wet weather, should I stop doing this, or open them less? Would it be better to close all the trickle vents too?

WestonDave

As we move into summer you'd expect indoor humidity to fluctuate more with the outdoor levels - because there is less ability to change it indoors. However its also less of a problem.


In winter if you have high indoor humidity there is a good chance that any cold surface will cause the relative humidity at that point to hit 100% and cause condensation, which if left leads to mould. That often happens for example on cold window panes during the winter, but it can also start to happen in cold corners of the room where warmth from heating doesn't reach.


In summer there are less of these cold spots around to set off condensation so its not such a problem. If the walls are staying reasonably warm then even if there is some minor condensation it will dry off again before mould can take hold. Its also harder to reduce humidity in summer without resorting to artificial means like dehumidifiers. In winter you can open the windows, let in cold air at high humidity and see the humidity drop as the heating system warms the air - (relative humidity falls as temperature rises for any given quantity of water in the air). In summer you don't have the heating on so you don't get that humidity drop by raising the temperature - which is why in general the levels in summer are much closer to the outside levels.

dominoman

If it's raining outside then the relative humidity of the air is around 100% (well actually it's a bit lower but not much), so opening a window will just push the humidity up inside the house.

Given the humidity levels you have reported there is no problem in your house.

I use automatic humidity sensors in every room, that report to my home automation system. The only dehumidifer I use is in the bedroom and it kicks in when humidity reaches 65%. I've set it to switch off at 60%.

If your humidity is showing at 55% and your house is at normalish temperatures then you don't have a problem and won't get mould.

TheCyclingProgrammer

Not sure where you read that the humidity should be below 40 OP. The ideal level is between 40-60 but there's no harm if it occasionally goes outside this range. Too low humidity can cause issues too.

cyclonebri1

You do not have humidity issues unless you have damp, smells, mould, litchen on the walls etc, IE, forget the measurements, do you see any symptoms??

If you have water running down the walls please forgive me, :A:A

brightontraveller

For those obsessed with humidity levels? This may help
Dew Point Calculator with guides as to chance of mold etc
http://www.dpcalc.org/