99% indoor humidity... what to do?

[daisy12345]

We've not lived in a house before (previously renting in flats) so still trying to get a handle on how to manage the humidity indoor. It's a 1930s end-of-terrace, with solid walls. I've read about the ideas of increasing ventilation and reducing moisture, so have got some measures planned out (dehumidifier on the way, will replace the recirculation hood in the kitchen with a chimney hood venting outside). Also we don't keep the radiators on all the time, to save some energy costs, only heating the home office which we mostly use to around 16C during the day and the bedroom to 15C overnight. However, this morning it turned quite warm (though raining) in London, so I thought it would be nice to ventilate the house a bit so I opened all the windows in the house. By the time I know it, the humidity reading went to 99% (from around 80%), and small water streams are running down quite a few walls (both external and internal)...... I suspect it's the warm air from outside meeting the cold walls (outside humidity is above 90% according to BBC weather)? What should I do then in such a situation (high humidity and warm outside) to manage the humidity levels inside the house please? Keep all windows shut and run the dehumidifier?

Any tips and advice would be much appreciated!

 

[JohnD]

I suspect it's the warm air from outside meeting the cold walls

If the walls were truly colder than the air, then, yes, water will condense onto the walls.

This circumstance is however quite rare in UK houses, except in bathrooms.

Have you got a bathroom extractor fan? Is it effective?

Do you drape wet washing inside the house?

You kitchen recirculator is purely ornamental, and serves no practical purpose. Is it on an external wall?

 

[daisy12345]

If the walls were truly colder than the air, then, yes, water will condense onto the walls.

This circumstance is however quite rare in UK houses, except in bathrooms.

Have you got a bathroom extractor fan? Is it effective?

Do you drape wet washing inside the house?

You kitchen recirculator is purely ornamental, and serves no practical purpose. Is it on an external wall?

Thanks JohnD. This morning it happened without me doing much cooking at all (fried an egg, that was it, which I did on most other days too which didn't cause such a dramatic increase in humidity). Bathroom extractor fans were installed when we moved in and seem to be working fine. We are drying some washing in the living room which is quite big hence less humidity and condensation problem so far. And yes, kitchen is next to an external wall hence it's the worst affected, together with the hallway which it's connected to.

I've now kept the front door and kitchen door open on both ends of the hallway, for half an hour, to let the wind blow a bit, but the hygrometer reading is still 99%....

 

[JohnD]

I see the temperature in London this morning was about 10C. Is your house truly colder than that?

https://www.metoffice.gov.uk/public...&fcTime=1612213200&zoom=8&lon=-0.97&lat=51.34

 

[daisy12345]

I see the temperature in London this morning was about 10C. Is your house truly colder than that?


https://www.metoffice.gov.uk/public...&fcTime=1612213200&zoom=8&lon=-0.97&lat=51.34

Overnight outside temperature was around 4C I remember, and indoor if the radiator is not on (well there's no radiator in the kitchen anyway) it's usually 6-7C on the north side of the house.

 

[JohnD]

It's usually considered that a house needs to be maintained around 12C. This will keep it dry. It will feel more comfortable if it is not damp, and this will prevent walls and wardrobes going mouldy. Fuel cost is very low at that temp, because, in England, the daytime temperature is often around 2C, so you are only heating it by 2C a lot of the time.

i recommend you stop draping wet washing inside.

If you have no alternative, rig up a line in the bathroom, and run the extractor fan continuously, with the door and window shut. This will take the water vapour outside and prevent it drifting round the house.

If the fan is noisy, we can fix that.

p.s.
@daisy12345
if you have a problem with high humidity and condensation, move furniture (especially wardrobes) away from external walls as they will be prone to mould on your possessions. There are some other steps too.

 

[Old Salt]

It must be damp inside the house for the humidity to be at 80%. I live in the SE and the humidity in my lounge is currently 52% and its been raining this morning. Personally I would partially open the windows in all rooms with internal doors open as well for an hour with the heating on and see what happens. We have the heating on varying between 16 and 20 depending on outside temp and time of day and the windows are open about 50mm every day normally in the morning whilst doing chores.

 

[^woody^]

From November to April, external humidity can be around 90% upwards, so the people that promote opening "the windows" to let fresh air in are chatting crap.

Water needs to be held within the air, and to do this air needs to be warm. As soon as air cools, it gives up the moisture on the coldest surfaces as condensation. After 11 hours in a specific situation of heat, moisture and still air , a damp surface starts to grow mould.

So the principles are that you need to keep the rooms sufficiently heated for long periods of time, not on-off type usage. The temperature will need to be determined by you, but it would normally be above 19°c daytime and evening and 14 at night.

Then you need to keep air moving. Not blowing a gale and not by opening windows wide, but by low ventilation most of the time, and rapid ventilation some of the time - cooking a bathing.

And any condensation on windows or cills needs to be mopped up straight away. Morning and night.

Don't fixate on outside temperatures, or at a certain temperature you must do a certain thing. You need to control the internal air, not worry about the external. And don't go around measuring humidity on a whim. You can have 100% humidity and no condensation or mould.

Generally, the person living in the home is causing the humidity. The building causes the condensation. You can do a lot to stop making the humidity, and you can do some things, but not all to stop the building making the condensation. So you must be prepared to do what you can to deal with the humidity you create, or live with the consequences - because you can't rely on the building changing.

 

[daisy12345]

It's usually considered that a house needs to be maintained around 12C. This will keep it dry. Fuel cost is very low at that temp, because, in England, the daytime temperature is often around 2C, so you are only heating it by 2C a lot of the time.

i recommend you stop draping wet washing inside.

If you have no alternative, rig up a line in the bathroom, and run the extractor fan continuously, with the door and window shut. This will take the water vapour outside and prevent it drifting round the house.

If the fan is noisy, we can fix that.

Thanks a lot for the advice! Maybe we'll keep the radiator in the hallway on all the time then. It's such a shame as the hallway is actually on the south side so should be getting quite good warmth during the day, but it's blocked by the porch outside, and it's on the external wall, so humidity is usually quite high. Will also consider running the dehumidifier there once we get it delivered....

 

[daisy12345]

It must be damp inside the house for the humidity to be at 80%. I live in the SE and the humidity in my lounge is currently 52% and its been raining this morning. Personally I would partially open the windows in all rooms with internal doors open as well for an hour with the heating on and see what happens. We have the heating on varying between 16 and 20 depending on outside temp and time of day and the windows are open about 50mm every day normally in the morning whilst doing chores.

Thanks. Will try turning up the heating a bit and see what happens... Usually we don't heat the rooms to above 16C... if it's sunny outside the rooms in the south do get to above 20C though

 

[JohnD]

if you find high humidity in one particular room, and it is not caused by steamy baths or excessive breathing, it can be a clue that there is a water leak. This may often cause steamy windows in the morning.

p.s.
12C is by my standards rather cool, but it will keep an empty house dry, and prevent the walls and fabric of the house getting very cold.

 

[daisy12345]

From November to April, external humidity can be around 90% upwards, so the people that promote opening "the windows" to let fresh air in are chatting crap.

Water needs to be held within the air, and to do this air needs to be warm. As soon as air cools, it gives up the moisture on the coldest surfaces as condensation. After 11 hours in a specific situation of heat, moisture and still air , a damp surface starts to grow mould.

So the principles are that you need to keep the rooms sufficiently heated for long periods of time, not on-off type usage. The temperature will need to be determined by you, but it would normally be above 19°c daytime and evening and 14 at night.

Then you need to keep air moving. Not blowing a gale and not by opening windows wide, but by low ventilation most of the time, and rapid ventilation some of the time - cooking a bathing.

And any condensation on windows or cills needs to be mopped up straight away. Morning and night.

Don't fixate on outside temperatures, or at a certain temperature you must do a certain thing. You need to control the internal air, not worry about the external. And don't go around measuring humidity on a whim. You can have 100% humidity and no condensation or mould.

Generally, the person living in the home is causing the humidity. The building causes the condensation. You can do a lot to stop making the humidity, and you can do some things, but not all to stop the building making the condensation. So you must be prepared to do what you can to deal with the humidity you create, or live with the consequences - because you can't rely on the building changing.

Thanks a lot Woody. I've read some of your other posts on this topic too and they've been very helpful, esp on humidity vs condensation and mould

Will see if turning up the heating can reduce some of the humidity meanwhile. Some articles say that it reduces energy cost to turn on the radiators only when you use the rooms, instead of having it on low settings all the time, but I guess that doesn't help keep the house dry in general.

 

[daisy12345]

if you find high humidity in one particular room, and it is not caused by steamy baths or excessive breathing, it can be a clue that there is a water leak. This may often cause steamy windows in the morning.

p.s.
12C is by my standards rather cool, but it will keep an empty house dry, and prevent the walls and fabric of the house getting very cold.

Yes there was a small leak in the pipe above the kitchen ceiling (which is worth another post....). That has been fixed and we are waiting for it to dry out before repairing the ceiling. So that could be contributing to the humidity issue too, but even with that on some days we only have around 70% humidity in there. Hopefully after the dehumidifier and the chimney hood it will improve.

 

[Harry Bloomfield]

Here there is a rule of no washing hung up indoors, except for in the utility which is set up for drying. Any moisture you generate in a house, will rapidly spread throughout the house in winter. Hanging clothes to dry anywhere in the living space, will spread the moisture throughout - it doesn't need much moisture to soak cooler walls. We have a well insulated semi and it is heated throughout and set up to never allow the temperature to fall below 16C. That is the nigh set back temperature, but because I have it well insulated, the heating never needs to come on during the night set back period.

SWMBO has a habit when cooking, of opening the inner door to the outside - we have two doors between kitchen and the outside. Between the two doors is a 9" wall which is cold in winter, but serves as a useful space to hang outdoor cloths. She only has to have that inner door left open for half an hour, for the wall and the hanging cloths to be wet through.

As above, recirculating hoods are a waste of money - they need to extract. Always cook with lids on pans. A fan in a bathroom is also a must have and must always operate when a bath or shower is used and for a while after - A PIR plus timer operated, plus humidity operated is worth having. In addition, a window needs to be opened a little, so there is some where for the air to come from. We leave a trickle vent opened, for a while after a bath, until the bathroom is dry.

Humidity in the house at the moment, with 3" of snow outside, is 46.

 

[daisy12345]

Here there is a rule of no washing hung up indoors, except for in the utility which is set up for drying. Any moisture you generate in a house, will rapidly spread throughout the house in winter. Hanging clothes to dry anywhere in the living space, will spread the moisture throughout - it doesn't need much moisture to soak cooler walls. We have a well insulated semi and it is heated throughout and set up to never allow the temperature to fall below 16C. That is the nigh set back temperature, but because I have it well insulated, the heating never needs to come on during the night set back period.

SWMBO has a habit when cooking, of opening the inner door to the outside - we have two doors between kitchen and the outside. Between the two doors is a 9" wall which is cold in winter, but serves as a useful space to hang outdoor cloths. She only has to have that inner door left open for half an hour, for the wall and the hanging cloths to be wet through.

As above, recirculating hoods are a waste of money - they need to extract. Always cook with lids on pans. A fan in a bathroom is also a must have and must always operate when a bath or shower is used and for a while after - A PIR plus timer operated, plus humidity operated is worth having. In addition, a window needs to be opened a little, so there is some where for the air to come from. We leave a trickle vent opened, for a while after a bath, until the bathroom is dry.

Humidity in the house at the moment, with 3" of snow outside, is 46.

Thanks! Point taken on the laundry hanging, though we haven't figured out what we can do about it yet...

Good insulation is a huge benefit. Unfortunately not sure what we can do with our solid external wall.. Have been reading about EWI and the risk of damp has put me off, for now.

So far haven't had much problem in the bathroom yet, as we do open the bathroom windows plus let extractor fan running for while. For the most of the day we also keep the windows of the bedroom open too to help ventilation (but we don't have the radiator on).

Kitchen is the biggest problem: north-facing, without a radiator, and next to an external wall. Not sure how much the upcoming chimney hood is going to help on that.