Best way to reduce high humidity in house

[lozcozard]

The humidity in my house is over 70%, and we have condensation on windows all day and moldy. I have been trying my best to get it down but it wont go, and I am confused why its not. I just wondered how best to do it when its now winter, and we are keeping heating off to save money, so house is cold.

- I have a positive input ventilation system blowing air in from the attic space, which should be pushing humid air out
- We put clothes outside to dry (we have a canopy for shelter) and not much on radiators - kids towels after showers in evenings. Finish clothes off in tumble dryer but thats vented outside.
- Have a bathroom extractor fan
- Have an extractor fan above oven
- We keep some windows like my bedroom and bathroom windows open slightly to get air in

- Outside humidity is 52% at 13C.
- Attic space is 64% at slightly higher temperature than outside
- upstairs in house varies between 69% to 74% at 17C to 18C.

So inside the house is much higher than outside, even though we have windows open.

Thing is, house is freezing due to posi vent and then of course windows open, and no heating on. Its 16C at the moment. Windows soaking from condensation still even next to open window.

I cant believe there is so much water in the house. The shower in the evening would produce a lot, but we have an extractor fan and bathroom window open.

Should we close the bathroom door AFTER showers to stop humidity entering rest of the house? The shower is the only major source of water vapour I can think of.

I would like to close our windows to keep heat in, but then humidity goes up, mid-70s.

Is all the humidity because we keep heating off most of the time? We treat ourselves in the evenings and put heating on for a few hours. Should we keep the heating on a lot more, keep the house warmer, windows closed, to evaporate off condensation? but then it all goes into the air so humidity would still be high and that will be expensive these days.

So I am looking for the best practice to keep humidity low, whether its a cold or warmer house? I dont know what else I could do.

Thanks

 

[Diver Fred]

Well, congratulations on a ventilation system but sounds like you should have a heat exchanging type that vents stale air outside and drains water away to a drain.

 

[foxhole]

Loft space could be humid if you have poor insulation, heat rises and warm air in loft will support more moisture .Bathroom fan may be inefficient , the small 4” fans tend to be feeble .

 

[DiyNutJob]

Lower temperature air carries less moisture. Hence lower humidity outside.

If the extractor fan in your shower room is whisper quiet, then you need one that sounds like a rocket. Also check the ducting isn't blocked.

Bad condensation on windows is caused by the internal glass pane of the double glazing attaining exterior temperatures. This can happen if the uPVC window is hollow and the cavity isn't sealed, allowing exterior temperature to reach the double glazing units. Old timber windows don't suffer from this. Not sure what the modern timber window is like.

One possible solution is a dehumidifier, if the humidity makes you physically uncomfortable with skin feeling sticky. But that can do nothing about the condensation on the window glass because of the reason explained.

 

[martygturner]

Lowering the temp of your boiler and heating the house gently but for longer stops water dropping out as it hits the cold window and saves money. Not having the heating on is unfortunately a recipe for condensation, by lowering the house temperature you are lowering the dew point of the air and hence making it easier for any moist air to condense. You are also making your house even colder...when we want to cool ourselves our bodies produce sweat..which evaporates and takes heat away...when water condenses the opposite happens heat is given up...in this case to the outside world via the window glass.

You have made a large fridge called house.

Keep doors and windows shut - open a couple of trickle vents , that should be enough for a house. Turn on the heating to low...let the house heat up slowly and then keep it warm...not hot warm. Even in our leaky house our boiler at 50 degrees uses £80 a month including the standing charge to keep the house at 19.5c from 12 noon to 8pm, residual heat keeps the place warm till 11pm, we have no condensation.

 

[Pat ex]

How long have you had your positive ventilation system? I'm assuming there was a problem that motivated its installation.
It can take many months for RH to be reduced if the house had high RH previously. The moisture is absorbed by the building's materials and fabric..
Lower or lack of heating would extend of the drying period.

Even empty homes with no heating suffer from condensation.

Are your windows double or single glazed?

Reducing RH works by bringing in cold air, heating it so that it can support additional moisture, then expelling that warm moist air, to be replaced again by dryer colder air.

You could try turning off the positive ventilation unit and use a dehumidifier. But you'd need to operate that set-up for at lease a month to notice any difference.

 

[Lower]

The humidity measurement RH is a relative percentage as air can hold more evaporated water when its warm than when its cold.

So, if you were to measure the humidity of a room at 20 degrees C and found it was 50% RH, then heated that room to 25 degrees without changing the amount of water in the air, the RH percentage would fall. Cool the air in that room in the same way and the RH percentage would go up. The lower the temperature, the higher the RH will go. When the air reaches 100% RH, it rains. If a patch of air locally hits 100% RH when in conctact with a cold surface, you get condensation.

Humans produce water vapour just by breathing and sweating. Cooking and bathrooms also produce lots of water vapour. If the house is warm and the windows, walls etc are warm then the air is able to hold more of that water without condensing than if the house is cold and walls and windows are cold.

In essence, unless you are able to ventilate away all the water that humans living in a house emit, you will get condensation if you don't heat the house. It will take a massive amount of ventilation to remove that water vapour laden air, which will make the house cold.

Simple answer is to heat the house to avoid the condensation. Or expect lots of condensation and when you do get mould, clean it away with a anti mould cleaner to kill the bacteria and avoid the associated health problems you get with lots of mould spores.

 

[lozcozard]

Thanks all for info and tips. I think I'll bite the bullet and try to keep house warmer and close windows. Just concerned about cost.

I think the humidity is coming down with the posi vent now turned on max but it is taking a while. A week later it's more often 65 to 70 than 70 to 75. So perhaps it is working. Some years ago I used one and only took couple of days.

My own bedroom window condensation is better now but I'm leaving my bedroom door open a bit at night too. My sons bedroom next door has door closed and he still has terrible condensation. Must be him sweating and breathing and towel in radiator.

My loft eves have condensation on the ceiling, so have slid these metal things in between the membrane to open it up to get more air flow in the loft. This may be one reason it's not lower in house.

 

[cwhaley]

We're in the same boat. Been in our house six years now and never had mould/condensation (after I insulated the upstairs bay window). Always understood the importance of warm rooms and the exchanging of stale air daily.

Unfortunately cannot afford to have the heating on anywhere like we used to, so the little lad's room has an oil-filled radiator keeping his room at 16-17 overnight which is nice and comfortable and results in no condensation. Downstairs is heating with burning timber. Our bedroom at night is usually around 10-12 degrees at the moment and there the windows/window board is covered in water in the mornings. Windows are left ajar 8 hours a day, with the wife wiping them down in the morning to manually remove as much water as possible.

I'm going to get an electric dehumidifier as it's the only thing I can think of as a reasonable alternative to spending hundreds and hundreds of pounds burning gas.

 

[winston1]

, so the little lad's room has an oil-filled radiator keeping his room at 16-17 overnight which is nice and comfortable and results in no condensation.

Very expensive assuming its electric. Electricity is 3 1/2 times the cost of gas.

 

[cwhaley]

Very expensive assuming its electric. Electricity is 3 1/2 times the cost of gas.

We'll find out on meter reading day!

There was a little thought behind it though. The oil radiator is electric, yes, but set at its lowest setting with the thermostat only about third of the way up, it manages to keep a comfortable temperature in the bedroom. With it being oil-filled, that oil holds temperature much longer than water would and it's obviously far more efficient than electric fan heater. So although the unit rate is higher for electricity, the number of units consumed is fewer than other options.

Whatever the cost, it's cheaper than burning gas all night along with an electric pump.

 

[winston1]

With it being oil-filled, that oil holds temperature much longer than water would and it's obviously far more efficient than electric fan heater.

Wrong. All electric heaters are 100% efficient whether oil filled or fan type. All the electricity consumed is converted to heat.

although the unit rate is higher for electricity, the number of units consumed is fewer than other options.

How can it be. If fewer units are consumed the temperature will be lower. Basic physics

Whatever the cost, it's cheaper than burning gas all night along with an electric pump.

You are not comparing like with like. You are comparing one room with a whole house.

so the little lad's room has an oil-filled radiator keeping his room at 16-17 overnight which is nice and comfortable and results in no condensation.

How about giving him more blankets and not heating the room so high?

 

[cwhaley]

Yes I understand the physics behind the conversion of different types of energy, but when an oil radiator switches off, it continues to radiate heat through the retention of it within the oil. When an electric fan switches off the heat stops.

I (genuinely) don't know if you have any children, but at seven months old simply "giving him more blankets" isn't safe nor advised. 16-17 degrees is a safe temperature and is why I use an oil radiator so he has a comfortable room.

With greatest of respect to you (as I know we've agreed on things and had good conversation before) I am going to terminate our discussion here, simply so that another innocent poster's thread isn't turned into back and forth, quote-for-quote arguing.

 

[winston1]

Yes I understand the physics behind the conversion of different types of energy, but when an oil radiator switches off, it continues to radiate heat through the retention of it within the oil. When an electric fan switches off the heat stops.

Agreed, but when you switch an oil filled radiator on from cold there is no heat radiation until the oil is heated

I (genuinely) don't know if you have any children, but at seven months old simply "giving him more blankets" isn't safe nor advised. 16-17 degrees is a safe temperature and is why I use an oil radiator so he has a comfortable room.

I have, grown up now. I grew up in a cold room with ice on the windows in the morning and survived. Though I think at 7 months I slept with my parents for warmth.

With greatest of respect to you (as I know we've agreed on things and had good conversation before) I am going to terminate our discussion here, simply so that another innocent poster's thread isn't turned into back and forth, quote-for-quote arguing.

OK, fair enough.

 

[foxhole]

Yes I understand the physics behind the conversion of different types of energy, but when an oil radiator switches off, it continues to radiate heat through the retention of it within the oil. When an electric fan switches off the heat stops.

I (genuinely) don't know if you have any children, but at seven months old simply "giving him more blankets" isn't safe nor advised. 16-17 degrees is a safe temperature and is why I use an oil radiator so he has a comfortable room.

With greatest of respect to you (as I know we've agreed on things and had good conversation before) I am going to terminate our discussion here, simply so that another innocent poster's thread isn't turned into back and forth, quote-for-quote arguing.

The oil takes a long time to heat up so on balance there is zero difference between a fan heater and oil heater.
There is nothing wrong with sleeping in an unheated bedroom, at any age.