Damp

[Frnc]

A dehumidifier won't help with the cause though, good ventilation and ideally where budgets allow use breathable paints & mortars in cellars.
We have a C16 place with cellars and fitted several low energy fans which circulate the airflow through the rooms and out and it has made a huge improvement, prior to that we had two dehumidifiers running constant (i hooked them up to condensate pumps to extract the moisture), the electric cost was considerable.

Are there two possible airflow directions in your cellar @frnc if so i'd personally look at having a small fan for intake and one for extract. Far far cheaper to run and maintain.

You are right. In the last few hours, it's warmed up outside, and humidity has dropped. I calculated the absolute humidity in the cellar and outside. It's 9.1 outside now, and 10.8 in the cellar. So the outside air is currently drier than the air in the cellar.

So I turned the dehumidifier off, peeled back the plastic on the unglazed window a bit (there are bars on top, so it would be difficult to do more and be able to stick it back), opened the kitchen window and the window in the room above the cellar. Air can pass freely through the butt jointed floorboards.

I'll look into maybe getting a better inflow and an extractor.

But if the absolute humidity is higher outdoors than inside, there's no good in letting air in. So I'll have to keep calculating the difference. Only takes a minute. If the humidity is high outside, it is probably worth running the dehumidifier. Seems a shame not to use it since I just bought it for this purpose.

Another factor is that if I decide to get another lodger in the room above the cellar, I can't have cold air going into the cellar in winter. Not unless I somehow seal the room above off. It has varnished floorboard, you can literally see through the gaps. I could seal them all, but it would be a big job.

Ironically it just started raining, this minute! But only lightly.

[tco-lincs]

You need to look at relative humidity not absolute. The humidity sensors can give you a misleading reading, the temperature within your home will affect how effective it holds moisture, so you may think its more humid outside so stop the ventilation, thats wrong keep the ventilation going. Mine is a slow and steady set of fans (120mm square) and this constant movement has made it far more noticeable, theres no smell and the "feel" is much better even without looking at the readings.

Peter ward has a series of videos explaining the cause and solution, https://www.youtube.com/watch?v=RbyaRgkfhwg

[Frnc]

You need to look at relative humidity not absolute. The humidity sensors can give you a misleading reading, the temperature within your home will affect how effective it holds moisture, so you may think its more humid outside so stop the ventilation, thats wrong keep the ventilation going. Mine is a slow and steady set of fans (120mm square) and this constant movement has made it far more noticeable, theres no smell and the "feel" is much better even without looking at the readings.

Peter ward has a series of videos explaining the cause and solution, https://www.youtube.com/watch?v=RbyaRgkfhwg

I'm not getting AH off the thermometers, I'm calcuating it. Thermometers measure RH.
In the video from about 9.30 to 12 minutes in, he says it is AH you want to be measuring. At 10.10 to 10.25 he says RH is 'a pretty useless measurement'. However I don't like his explanation of RH at 10.30, maybe he got his words mixed up. I think he explains it better later. Fact is that if you cool a parcel of air, its RH will increase, but AH stays the same. If you warm a parcel of air, it's RH will decrease, but its AH will again stay the same. So RH is temperature dependent. AH is not. Not in the sense we are talking about here, anyway.

He says AH of 7g/m3 is dry, and 12 is wet, and will rot your timbers. My cellar is currently 10.3. Air outside is 9.4, so it's drier than my cellar, so it's good to be letting it in. He says that if the air outside is too damp, you can move air from a dry room indoors into your cellar. Easier said than done, but air can get in from the hall and front room via gaps in floorboards. I've put the kitchen extractor on full blast, to hopefully drag damp air out. Cellar door is open but living room door is shut shut.

Air in the hall is 9.3, so it's good that can get into the cellar through gaps in the floorboards. I don't have a digital in the front room, but the window is open.

[Frnc]

Trying to reduce the RH in my house, as it's 60-70 upstairs, which is a bit high. I don't want mould.

So I've put the laundry outside even though it's only 9°. There is a breeze, and it's been sunny some of the time, so hopefully they'll be nearly dry when I bring them in.

I'll put them in the living room. Then the C/H should kick in for the evening, and I'll put the kithen extractor on while I make my tea and do the washing up. So hopefully most of the moisture will go out that way. I could put a fan in the living room to push the air into the kitchen.

Then I'll turn the fan round, open the other living room door, and bang the dehumidifier on the landing on for a couple of hours.

[GillyBee]

Have you tried out the traditional airing the house out every day system. Mrs Beeton recommended it and it is apparently standard in Germany.
[url]https://www.walesonline.co.uk/news ... n-28600086[/url]

And Mrs Beeton tells ladies maids to do this this:

Every morning, immediately after her mistress has left it, and while breakfast is on, she should throw the bed open, by taking off the clothes; open the windows (except in rainy weather), and leave the room to air for half an hour.

[Frnc]

Have you tried out the traditional airing the house out every day system. Mrs Beeton recommended it and it is apparently standard in Germany.
[url]https://www.walesonline.co.uk/news ... n-28600086[/url]

And Mrs Beeton tells ladies maids to do this this:

Every morning, immediately after her mistress has left it, and while breakfast is on, she should throw the bed open, by taking off the clothes; open the windows (except in rainy weather), and leave the room to air for half an hour.

I am doing, but you need to check the Absolute Humidity first. For example, today, Relative Humidity is high in the Prep Room as usual, but actually its AH is lower than outside, so opening the window would do more harm than good. Outside is damp and not very cold today. Ironically, when it's cold, AH will be low, so it's usually worth opening the window. Forecast shows RH. I use this online converter https://planetcalc.com/2167/#google_vignette

I will open windows at 2pm, as AH outside will have dropped from 10.0 to 5.9.

[Frnc]

Up at 4.30 am. Humidity in my room was 64%. Outside was 92%. However, I opened my window for 15 minutes, and my room's humidity dropped by 5%. How is this possible, if outside humidity is much higher? Because 92% at 7° converts to 7.2g of water per cubic m of air, whereas 64% at 18.9° converts to 10.8g/m3. You need to convert, and understand that cold air is usually drier.

Prep room RH is 70%, a definite mould risk, so I've opened it's window.

RH needs to be ideally around 50% indoors. At 70% there is increased risk of mould.

AH seems to be mostly lower outside now, but not always. So I check before opening windows, as I don't want to bring cold air in if it won't dry the house.

But the cellar is more of a faff, so I'm leaving the window so air can get in all the time at the moment. I'm going to partially close it, so just a trickle of air can get in during the winter. The cold outside air will have a low AH in winter, but I have to think about heating costs.

[Frnc]

Going to calibrate the hygrometer bit of all my themometers tomorrow.

Method.

Mix teaspoon a pure salt with few drops of water to a paste/slurry.

Put salt paste in small cup.

Put in plastic bag with hygrometers.

Seal bag

Leave 12 hours.

All should read 75%. If one reads, say 72, you make a note or sticker saying 'add 3%'.