humidity in house

joeyhalloran

We live in an old, 1930s semi detached house with poor insulation, we've done what we can by blocking up vents to prevent draughts and the fireplaces have been removed.

Today the absolute humidity is higher inside the house despite having all the windows open most of the day and the back door open this afternoon, no one has showered and we have only cooked porridge at breakfast, no clothes were hung/dried inside (though some were washed and dried outside) and there are no apparent water leaks. Why is the humidity still higher inside than out?

It's always high, ~70+% and we get condensation on the windows in winter but no signs of mould anywhere but it feels a little odd when all the windows are open?

orraloon

Check the external humidity % figures. E.g. use netweather.tv website, others are available. I've just looked at my location, it's not raining but the figure is 97%... 🤔

rjsterry

Blocking up the vents is a really bad idea. Ideally all the air in your living spaces should be changed 6-8 times an hour. The further you get away from that the more water vapour produced by normal daily activities will accumulate. At 70% for any length of time you will start to get mould growth. Ideally internal RH (relative humidity) should be close to 50%. If the house is poorly insulated, that higher humidity will also lead to condensation once the external fabric gets down below about 12°C. Some materials (especially very alkaline ones like lime plaster) can inhibit mould growth but it's really just a question of when you get more serious problems without good ventilation.

At a basic level all your windows should have trickle vents and bathrooms, toilets, utility rooms and kitchens should all have extractor fans or a cooker hood (not just recirculating) and these should be operated with the lights or by a humidistat.

You do of course waste some heat with this system, but it should maintain a more healthy internal environment. To save energy there are fans with heat recovery - either via a centralised ducted system or there are individual fans with heat recovery. They extract as normal but pass the air through a heat exchanger. Periodically the fan reverses and brings in fresh air, heating it via the heat exchanger.

To answer your specific question, relative humidity is usually higher internally due to habitation. If you have been living in the house with poor ventilation for an extended period, the building fabric will have absorbed quite a bit of water vapour, and will release that into the internal air through evaporation.

Hope that's helpful, but let me know if you have any other questions.

BTW, it is just very humid at the moment.

briantrumpet

orraloon said:

Check the external humidity % figures. E.g. use netweather.tv website, others are available. I've just looked at my location, it's not raining but the figure is 97%... 🤔

Is that relative or absolute humidity (I suspect the former)?

What gives away humidity in my house is pure cotton bedding... without any heating in my bedroom (I've never had any in 59 years), when the temperature falls and with a damp atmosphere, the bedding quickly gets, erm, 'not so pleasant', until it's warmed up. Perhaps I ought to get the butler to warm it with one of these...

webboo

Pure cotton bedding. I thought you’d be more of a sacking as bedding and hair shirts type of guy.

TheBigBean

Warmer air holds more moisture, so if it is warmer outside than inside, you would have higher humidity inside given the same air. Usually it is warmer inside, so the opposite is true.

joeyhalloran

So what i meant was when we convert the relative humidity inside and outside using internal and external temperature to absolute humidity we still have higher humidity inside. I understand ventilation is very important to combat this but we've had all the windows and doors open today (have had for the last few months basically).

The rel humidity round me is currently 87% at 18c so it's hard to combat it too much and obviously doesn't make much sense increasing the temperature of the house to when it's already warm.

The real humidity inside is regularly 70 and above since we moved here two years ago with no sign of mould anywhere.

I've been wondering about getting a PIV unit but I don't see what that will do Vs opening all the windows?

Or perhaps try and make the house more airtight and fit a MVHR but they're pretty spendy. Though we are looking to make some environmental improvements so it's either that or external insulation (not sure we could stretch to both). I've heard MVHR can actually be more affective than extra insulation but I'm not sure how easy it is to retrospectively make a building more air tight.

briantrumpet

webboo said:

Pure cotton bedding. I thought you’d be more of a sacking as bedding and hair shirts type of guy.

I was given a John Lewis voucher, so decided to try posh.

joeyhalloran

oxoman said:

When you removed the fire places did you block them up top and bottom if so this can cause problems. You must vent top and also bottom of each fire place / chimney flue. I made the mistake of only venting the old fireplaces and suffered with damp etc even though chimney stack removed to below roof level. Didn't resolve itself until I reopened the top of the flues in the loft.

I don't think either of the tops are capped, one has a vent and the other has a loosely fitting mini-bookcase for my daughter's books in so gets at least some airflow.

super_davo

Where I live is coastal and there is often high humidity outside.

So all the windows open / open vents etc just end up pumping your house with fresh but damp air. When it's like that... that's where a dehumidifier helps. I don't run it all the time, but it's great at getting the humidity down from 70+ to under 60 quickly then decent ventilation keeps it there.

I would definitely recommend having one in your armoury to keep things under control as if you're in the 70+ range for an extended period of time and your sofas / carpets / curtains / bed pick up moisture, it can be very hard to deal with using ventilation alone.

joeyhalloran

We have a desiccant dehumidifier but they only really work well when it's cold. We use it during the winter and it nicely heats my office when working from home as a bonus but it doesn't seem to make much of a dent in the humidity figures. It's only a relatively small one though, but it is a which best buy.

rick_chasey

I bought a proper dehumidifier, can't remember if it's desiccant or refrigerant, about 8 years ago now, when I had no-where to dry clothes but inside.

I do find it very helpful in the winter. Doesn't need to be on all the time, just when there's a lot of water activity in the house, so cooking or drying washing.

Makes a big difference to comfort in the house too. Obviously you don't want to go super dry, but dryer air is warmer.

Can recommend it. Plus the water it collects is great for washing windows.

Jezyboy

We have a beefy refrigerant dehumidifier from Aldi. So far it's worked pretty well for 5 years in various Victorian houses

shirley_basso

Does it make a big difference wrt heating as well? I think our upstairs is a bit damp so would be helpful to run on a timer (maybe 1h before the heating comes on, for example)

TheBigBean

rick_chasey said:

Can recommend it. Plus the water it collects is great for washing windows.

Why?

rjsterry

TheBigBean said:

rick_chasey said:

Can recommend it. Plus the water it collects is great for washing windows.

Why?

No limescale.

JimD666

shirley_basso said:

Does it make a big difference wrt heating as well? I think our upstairs is a bit damp so would be helpful to run on a timer (maybe 1h before the heating comes on, for example)

Yes. Dry air is easier to heat.

Getting close to running ours 24/7. Price to pay living this close to the coast

rick_chasey

deionised water innit.

joeyhalloran

Im now wondering if it a good middle step is replacing extractor fans with single room heat recovery fans and leave them running 24/7

TheBigBean

rjsterry said:

TheBigBean said:

rick_chasey said:

Can recommend it. Plus the water it collects is great for washing windows.

Why?

No limescale.

Learn something every day.

Pross

Think I'm going to get one for my office. As I mentioned last year it is what used to be the garage and is single skin, it's starting to smell a bit damp out here and hopefully a desiccant type will help heat the area around my desk which would be more efficient than the oil filled radiators. Hoping it would also help with drying clothes through the winter months.

First.Aspect

rick_chasey said:

I bought a proper dehumidifier, can't remember if it's desiccant or refrigerant, about 8 years ago now, when I had no-where to dry clothes but inside.

I do find it very helpful in the winter. Doesn't need to be on all the time, just when there's a lot of water activity in the house, so cooking or drying washing.

Makes a big difference to comfort in the house too. Obviously you don't want to go super dry, but dryer air is warmer.

Can recommend it. Plus the water it collects is great for washing windows.

A "proper" dehumidifier is basically an ac unit that repeats the air. Not the most environmentally friendly.

Air with higher humidity is a better conductor if heat. So it's either "warmer" or "colder" in terms of ones perception, depending on its absolute temperature compared to you.

TheBigBean

Pross said:

Think I'm going to get one for my office. As I mentioned last year it is what used to be the garage and is single skin, ot's starting to smell a bit damp out here and hopefully a desiccant type will help heat the area around my desk which would be more efficient than the oil filled radiators. Hoping it would also help with drying clothes through the winter months.

They were completely sold out last winter, so you might want to buy earlier. Alternatively, there could be a glut of them, so if you wait you'll get one cheaply in the Jan sales.

joeyhalloran

First.Aspect said:

A "proper" dehumidifier is basically an ac unit that repeats the air. Not the most environmentally friendly.

Air with higher humidity is a better conductor if heat. So it's either "warmer" or "colder" in terms of ones perception, depending on its absolute temperature compared to you.

Except that in summer high humidity prevents sweat from working as well so it might end up feeling hotter.

briantrumpet

TheBigBean said:

Pross said:

Think I'm going to get one for my office. As I mentioned last year it is what used to be the garage and is single skin, ot's starting to smell a bit damp out here and hopefully a desiccant type will help heat the area around my desk which would be more efficient than the oil filled radiators. Hoping it would also help with drying clothes through the winter months.

They were completely sold out last winter, so you might want to buy earlier. Alternatively, there could be a glut of them, so if you wait you'll get one cheaply in the Jan sales.

Plenty on Amazon right now. Having read this discussion, I've gone for a 150W one with good reviews for the bedroom, to keep the bedlinen dry when the temperature drops... reading the reviews, it looks like a couple of hours a day should do the trick.

First.Aspect

joeyhalloran said:

First.Aspect said:

A "proper" dehumidifier is basically an ac unit that repeats the air. Not the most environmentally friendly.

Air with higher humidity is a better conductor if heat. So it's either "warmer" or "colder" in terms of ones perception, depending on its absolute temperature compared to you.

Except that in summer high humidity prevents sweat from working as well so it might end up feeling hotter.

Isn't that what I just said?

TheBigBean

briantrumpet said:

TheBigBean said:

Pross said:

Think I'm going to get one for my office. As I mentioned last year it is what used to be the garage and is single skin, ot's starting to smell a bit damp out here and hopefully a desiccant type will help heat the area around my desk which would be more efficient than the oil filled radiators. Hoping it would also help with drying clothes through the winter months.

They were completely sold out last winter, so you might want to buy earlier. Alternatively, there could be a glut of them, so if you wait you'll get one cheaply in the Jan sales.

Plenty on Amazon right now. Having read this discussion, I've gone for a 150W one with good reviews for the bedroom, to keep the bedlinen dry when the temperature drops... reading the reviews, it looks like a couple of hours a day should do the trick.

Many of them have auto settings, so you can have them come on at a certain level of humidity.

joeyhalloran

First.Aspect said:

joeyhalloran said:

First.Aspect said:

A "proper" dehumidifier is basically an ac unit that repeats the air. Not the most environmentally friendly.

Air with higher humidity is a better conductor if heat. So it's either "warmer" or "colder" in terms of ones perception, depending on its absolute temperature compared to you.

Except that in summer high humidity prevents sweat from working as well so it might end up feeling hotter.

Isn't that what I just said?

And yes, I meant to say AND instead of EXCEPT

joeyhalloran

https://www.appliancesdirect.co.uk/meaco_8l_desiccant_dehumidifier_electronic_control_dd8ljunior/version.asp

This is the one we have.

super_davo

Meaco are generally regarded to be the best but 8litres / day isn't very much.

Desiccant are great for cold environments like sheds and outbuildings. I'd say that capacity is more suited to that use too.

For a house, you'd probably get more success from a refrigerant model - they work better above 15degrees or so. I've got a Blyss 20 litre model that cost about £100 from Screwfix. It's big enough to cover either the upstairs or the downstairs of my house; I run it for a few hours every few days when the humidity gets up and move it around.

joeyhalloran

It says on the website it's suitable for a 5 bedroom house...