Humidity questions

[Tlandcruiser]

I have a temperature gauge with a built in humidity meter which has been reading quite high, yesterday it was reading 79% (outside weather app said 99%) and today its reading 62%. Searching Google suggests 50% humidity is what the house should be, but how is it possible to have a house with 50% humidity if the outdoors humidity is 99%? how does the outdoor humidity levels effect the indoors humidity?

Today, the temperature is 14c with a humidity level advertised as 62% could the house be lower than that?

I have no damp or mold, the windows do get a little condensation but I put that down to being old double glazing with large windows..most of the windows are almost 3m long and quite tall.

The kitchen does not have an extractor fan, so I know that will contribute to the humidity unless the window are open to ventilate. My small bedroom window is open 24/7 as I like the room to be cold, the back door is open alot but I could ventilate other rooms more. The oven is gas with a gas hob, so that til will increase the humidity.

House Details:

1960s detached bungalow with a suspended wood floor
Cavity walls
double glazing
No damp/mold
Gutters are clear and I dont have water sitting by the house nor is the dpc bridged anywhere

Im not sure what else to check? or is it a problem? I dont want to buy a humidifier,

Edited by Tlandcruiser on Tuesday 22 October 15:51

[clockworks]

50% sounds quite low. My house (1960's bungalow) is generally around 60 to 65%

[Equus]

Tlandcruiser said:

Searching Google suggests 50% humidity is what the house should be, but how is it possible to have a house with 50% humidity if the outdoors humidity is 99%?

Firstly, there is no 'magic number' for relative humidity. Unless you use air conditioning (which can control humidity levels by condensing out the moisture from the air) it will be what it will be.

Secondly, however, what you're measuring is relative humidity; ie. the percentage of the total amount of moisture that the air can hold.

Air can hold more moisture when it is warm than when it is cool, so if you take external air at (say) 90% humidity and warm it up inside your house, its capacity to hold moisture increases, therefore the relative humidity figure drops as it warms up.

But so long as you don't have noticeable problems with mould or condensation, don't sweat it.

[Tlandcruiser]

Equus said:

Firstly, there is no 'magic number' for relative humidity. Unless you use air conditioning (which can control humidity levels by condensing out the moisture from the air) it will be what it will be.

Secondly, however, what you're measuring is relative humidity; ie. the percentage of the total amount of moisture that the air can hold.

Air can hold more moisture when it is warm than when it is cool, so if you take external air at (say) 90% humidity and warm it up inside your house, its capacity to hold moisture increases, therefore the relative humidity figure drops as it warms up.

But so long as you don't have noticeable problems with mould or condensation, don't sweat it.

Thanks Equus,

So on days with lots of rain and high humidity, the indoor level will be higher too and my gauge is only displaying how much water the air can hold before it condensates??? so the actual humidity level could be lower?

The meter did suprise me because I do not get mold or damp issues which I did associate with high humidity

[Equus]

Tlandcruiser said:

So on days with lots of rain and high humidity, the indoor level will be higher too...

Probably, but not necessarily - it also depends on other factors, such as the difference in temperature between internal and external, and the amount of moisture being added to the air, internally.

Tlandcruiser said:

....and my gauge is only displaying how much water the air can hold before it condensates???

It is displaying the percentage of the moisture that the air can hold before it condenses at ambient temperature. But that is the 'humidity level'. The actual amount (mass per cubic metre) of water that air can hold depends on the temperature and pressure of the air.

Whether condensation occurs depends on other factors, and is complicated. At one extreme, you could (theoretically) have 95% humidity in a building, but no condensation occurring; at the other you could have 25% humidity, but certain surfaces streaming with moisture. If you have certain surfaces that are significantly cooler than ambient temperature, condensation can occur on them even if the relative humidity in the ambient air is well below 100%.

If you are desperate to understand it, go do a Degree in Building Technology. Otherwise, if there is no visible problem, forget about it.

Edited by Equus on Tuesday 22 October 18:53

[jimmyjimjim]

clockworks said:

50% sounds quite low. My house (1960's bungalow) is generally around 60 to 65%

PMSL!

Currently running at 12-17% here.

I've literally just added a humidifier in the hope of getting it up to ~30%.

[98elise]

jimmyjimjim said:

clockworks said:

50% sounds quite low. My house (1960's bungalow) is generally around 60 to 65%

PMSL!

Currently running at 12-17% here.

I've literally just added a humidifier in the hope of getting it up to ~30%.

I thought fk that's low...then checked where you lived!

50-55% indoors just about perfect in the UK, but unless you're getting condensation/damp then it can go quite a bit higher without issues.

Edited by 98elise on Wednesday 23 October 12:28

[Tlandcruiser]

98elise said:

I thought fk that's low...then checked where you lived!

50-55% indoors just about perfect in the UK, but unless your getting condensation/damp then it can go quite a bit higher without issues.

How is it possible for a house to have readings that low? Even in my last house I had high levels.

[jimmyjimjim]

Current external humidity is ~25%.

[98elise]

Tlandcruiser said:

98elise said:

I thought fk that's low...then checked where you lived!

50-55% indoors just about perfect in the UK, but unless your getting condensation/damp then it can go quite a bit higher without issues.

How is it possible for a house to have readings that low? Even in my last house I had high levels.

Do you mean 50-55%?

It's easily possible. RH driven by a lot of factors. Ventilation, heating, drying clothes, showering, breathing etc.

Our house is generally 55-60% in the winter months.

[Equus]

jimmyjimjim said:

Current external humidity is ~25%.

For tha avoidance of confusing the OP any more than he already is, PistonHead's forum can't cope with the 'around' symbol and is converting it into a 'minus'.

You can't have a negative relative humidity of course.

But we never see figures as low as 25% in the UK's maritime climate.

[Sheepshanks]

Tlandcruiser said:

Today, the temperature is 14c with a humidity level advertised as 62% could the house be lower than that?

If you're at home, open the windows front and back for 5-10 mins, then shut them again. This - assuming there's a bit of air movement, unlike this morning where it's completely still here (Cheshire) - will change the air for the colder and lower absolute humidity air outside. Once you shut the windows, the house will recover its temperature quickly and as the air warms up its RH will drop.

I find the snag with leaving bedroom windows open all night is the inside of the double glazing gets cold and mists up. Having said that, excess humidity will find somewhere to condense so the glass is probably the best place. The meter I have also displays dew point and right now it's saying 13.3C. Inside temp is 20C. Outside temp is 6C. Inside RH is 66%, but everyone's not long been up, had showers etc. It's usually high 50's.

[jimmyjimjim]

Equus said:

jimmyjimjim said:

Current external humidity is ~25%.

For tha avoidance of confusing the OP any more than he already is, PistonHead's forum can't cope with the 'around' symbol and is converting it into a 'minus'.

You can't have a negative relative humidity of course.

But we never see figures as low as 25% in the UK's maritime climate.

Really, it shows for me - how odd!

[dingg]

~~~~~~~~~
Works for me too

[Sheepshanks]

jimmyjimjim said:

Really, it shows for me - how odd!

Works for me, too.

The dew point must be very minus in centrigrade - and possibly even in Fahrenheit.

[Tlandcruiser]

I’ve been reading a lot on the subject and gaining a bit more understanding.

I think the majority of the humidity is due to lifestyle and not ventilating the bungalow enough especially the kitchen where so much humidity comes from due to the lack of extractor ( plan on extending and moving the kitchen) otherwise I would have installed one already.

Repealed round the double glazing as the silicone looks pretty bad and maybe allowing rain in..

Loft has no soffit vents and just lap vents, I don’t know if that might impact it?? But I’ll add soffit vents.

I wanted to lower it because if I add a rimless aquarium, I don’t want to increase the humidity to much

[Equus]

Tlandcruiser said:

Loft has no soffit vents and just lap vents, I don’t know if that might impact it??

In theory there should be no interchange of air between the habitable space and the loft space, but if it happens, it will always (due to vapour pressure) be warm, moist air from inside the house leaking into the loft, not the other way around.

Soffit vents can help disperse condensation in the loft, but they'll have no impact on condensation or mould growth within the house.

[Tlandcruiser]

prior to cooking the humidity was 60%, once my wife started cooking with the window open it still rocketed to 80% before I stopped measuring. I'll fit a cooker extractor because the planned kitchen/extension is not until next year or in two years time. Then that mositure rich air gets circulated around the bungalow quite quickly as its only 100sm.

[Martin_Hx]

Im forever telling the Mrs to open a window and put the fan on when having a shower/cooking and keeping the doors shut but she never listens!

I have a small (pretty crap) dehumidifier which is running constantly which fill up in around 2 weeks and i have a large one which i put on if im drying clothes etc and i set it to 65% - we have some single glazing still in the house which sometimes has condensation but these are being replaced as we speak!

[Equus]

Tlandcruiser said:

I'll fit a cooker extractor....

Yup, cooking generates a huge amount of moisture, and a direct extract from a cooker hood makes a big difference.

The other biggies in terms of internal moisture generation are showers and laundry: use a humidistat operated extract fan in bathrooms/shower rooms and do NOT dry laundry in the house.