Condensation & Humidity

Terry98

I am trying to understand condensation in relation to humidity.

We have a problem with condensation in two rooms which we are trying to sort out. I have bought a cheap humidity meter which shows that both rooms average between 75 and 90% humidity. Opening the windows and putting on the dehumidifier can get that down to about 60% but I am trying to find out the source rather than temporally sorting out the problem.

This morning we did not have any condensation although both rooms were showing between 75 and 90% humidity.A couple of days ago the windows were streaming with condensation but the humidity was the same!

I thought higher humidity equals more condensation but this must be wrong. Could someone explain where I am going wrong.

Chunks

No expert but when it's cold outside, condensation forms on some of my windows. As it warms up (outside) the problem lessens (the opposite is also true). Humid air meets cold surface equals condensation.

Nigh on impossible to avoid in my house but reducing the sources of humidity (dry washing outside, ditto wet towels and ventilation) all help.

saveallmymoney

The concept you are looking for is "Dew Point", if the window temperature is below this you will get condensation.

http://www.dpcalc.org

DRP

Really cold days = more condensation on windows etc


You say you are looking for the source of the high humidity - can you give more information about the house?

New/old?
terrace?
Is it heated adequately?
Cavity wall insulation fitted?
Do the 2 rooms face north/are they in an exposed position?
Concrete or suspended wooden floor?
How high are outside ground levels?
Do you have air bricks or other ventilation?
Gutters and roof in good nick?


As an example, our high humidity in the hall of 65-85% is due (i think) to a combination of historical leaking gutters, lack of ventilation and the attached neighbour's drive being higher than ours...

dampdaveski

Terry,
Don't get hung up on your meter is the first thing!
You have relative humidity which is a measurement of the amount of moisture in the air at a given temperature.

To make understanding this a bit easier imagine the following

Get a dry bathroom sponge and imagine the sponge is air at 20 deg c
Then put a dry flannel next to it and imagine this is air at 15 deg c
Pour 100ml of water into the sponge, this will soak it up and to all intents and purposes it will still look like a dry sponge.
Pour 100ml of water into the flannel and it will immediately get very wet and most of the water will run straight through it.
This is because the flannel (or air at 15 degc) cannot hold the same amount of water that the sponge can (air at 20 deg c)

So warmer air can hold more moisture (humidity) than colder air.
The colder air has to deposit that humidity out as liquid water (ie it condensates into liquid) because it doesn't have the ability to hold as much moisture.
Hopefully that makes a bit of sense
DD

Terry98

Some great advice. Thanks very much.

The house is well heated and does have cavity wall insulation but one of the bedrooms does face north! Although heating is on in this room it's only on low because we don't like it hot!

We are going to get fans fitted in the bathroom and the kitchen and will dry the washing in a condensing tumble dryer to see if that help the problem.