In house humidity

[5 In a Row]

I recently bought a late Victorian house and wonder what sort of humidity I should expect in the rooms, especially those downstairs?
Regular readings for a large room that is used in frequently are around 65%.

The house has gas central heating and 4 year old wooden sash double glazed windows but has otherwise not had a lot done to it for probably 25 years.
Some of the radiators are recentish but half are old single panel ones.

I have one of these humidity/temperature setups but I'm worried that since it was cheap it might not be accurate
https://www.bresseruk.com/p/national-geographic-th...

For example if I put the small sensors beside each other they rarely give the same readings - temperature can be more than 1 degree different between them for example.

Any pointers happily accepted.
Thanks in advance.

[RGG]

I'm no meteorologist but, humidity has a relationship to temperature.

The significance of your reading would be directly related to your temperature in the room.

Your 65% reading doesn't necessarily mean the room is damp - is this what you are thinking?

It's 75% humidity here right now but 1C temperature.

The warmer the air the more moisture can be contained.

The lower the temperature the less moisture can be contained - thus cold air becomes saturated more easily.

Your reading will be related to room temperature and also outside temperature.

Someone who really knows about this and can articulate it better will be along soon.

[Craikeybaby]

Ideally you want <60% to avoid mould on walls.

[jimmyjimjim]

You don't want it too low, though. I've had below 10% several times. On one notable occasion when it got low, I smote the DVD player with a lightning bolt that almighty Zeus himself would have been proud of, killing it, and numbing my hand for several seconds. Had to dismantle the player to get the disc out.

[Byker28i]

we run our dehumidifier at 55%. We chased leaks for 6 years in our welsh cottage and once we fixed all those it was easy to keep it to that. Before that we were pulling 5 litres of water every 12 hours

[5 In a Row]

Thanks all.

I WAS worried that a high reading indicated likelihood of damp but the rooms are generally a bit colder than we're used to in newer houses and the last similar house we had was back in 2007/8 so I can't remember temps plus we never had anything to measure humidity.

Even with a fairly new dehumidifier we're pulling out around 200ml of water in an hour in a room that's 23ft by 13ft and has high ceilings.

We had a Dorran house - 1960s build with precast concrete slab walls bolted to a steel frame (that invariably rusts) and wall thickness, including inner plasterboard, of under 10cm - years ago and after a while discovered mould behind freestanding furniture that was against the walls so we're always wary of that situation. There's no evidence of anything like that just now.

[Road2Ruin]

The training room in my office is always 80ish%. Never had a problem with damp or mould. It's more about air circulation and cold spots on surfaces.

[robemcdonald]

You might consider positive input ventilation.

Many units on the market. There is a thread on here about a particular one and there is a discount for PH members.

[MajorMantra]

Have you got sufficient ventilation? Sometimes people make old houses too airtight with newer windows etc, which leads to humidity problems. Do the windows have trickle vents? Is there extraction in the kitchen and bathroom?

If you want to seal up an old house to modern standards of draught-proofing, you generally need to introduce some form of active ventilation to avoid issues, but even stuff like trickle vents makes a difference.

[5 In a Row]

MajorMantra said:

Have you got sufficient ventilation? Sometimes people make old houses too airtight with newer windows etc, which leads to humidity problems. Do the windows have trickle vents? Is there extraction in the kitchen and bathroom?

If you want to seal up an old house to modern standards of draught-proofing, you generally need to introduce some form of active ventilation to avoid issues, but even stuff like trickle vents makes a difference.

The windows don't have trickle vents but there are still plenty of drafts, for example where the cord for the bottom window comes out of the frame.
Plus the windows have been getting opened periodically to air the house.

Bathrooms and kitchen have extractors.

I don't think a positive input system is feasible at the moment.

I think I'm probably just being over cautious at the moment because of my lack of knowledge/experience about the humidity readings.
I might take one of the sensors with me whenever I go to other houses and see what the readings are there

[Simpo Two]

I have a dehumidifer running in the garage, with a drain to the outside so it can stay on 24/7.

I remember the instructions saying don't use it in cold weather - can someone explain that in terms of temp vs humidity?

[bigpriest]

I'm in a 1910 end terrace in NW - general readings are around 50%, can rise to 65%-70% if it rains. I have plenty of ventilation via chimneys so never see a trace of mould.

You have a very small window of opportunity in July / August when you can gloat about how cool your north facing room is when everywhere else is sweltering.

[Craikeybaby]

Simpo Two said:

I have a dehumidifer running in the garage, with a drain to the outside so it can stay on 24/7.

I remember the instructions saying don't use it in cold weather - can someone explain that in terms of temp vs humidity?

There are a couple of different types of dehumidifier, one is more suited for use in colder temperatures, as it has a heating element. However they are more expensive to run.

[ARH]

Craikeybaby said:

Simpo Two said:

I have a dehumidifer running in the garage, with a drain to the outside so it can stay on 24/7.

I remember the instructions saying don't use it in cold weather - can someone explain that in terms of temp vs humidity?

There are a couple of different types of dehumidifier, one is more suited for use in colder temperatures, as it has a heating element. However they are more expensive to run.

Its because a dehumidifier works by creating a cold surface for condensation to form on, remember that is how condensation is created. Therefore if its cold and you make water colder if goes solid and it then has trouble dripping out of the pipe.

[POIDH]

I put a new roof on my old house - the humidity indoors reduced over the next few months steadily even though it was heading into winter.
I also dug French drains around all external walls, and ensured that the water was guided away from the house. Again, you could see the downstairs condensation and humidity levels drop over the course of a few months.
We had bought a house with some condensation, mould and two damp rooms issue.
Ten years later there is one wall that remains stubbornly damp, which funnily enough had a flower bed and wall built within a few cm of the house. If I had stayed, that was being removed shortly.

I think you have to be so fussy about where water, rain and damp can penetrate or sit on a building. If you can shelter, move water away and waterproof better, it can stop a lot of moisture getting in.

Then again, the house is fully of watery bags of flesh who insist on keeping breathing...

[Simpo Two]

ARH said:

Craikeybaby said:

Simpo Two said:

I have a dehumidifer running in the garage, with a drain to the outside so it can stay on 24/7.

I remember the instructions saying don't use it in cold weather - can someone explain that in terms of temp vs humidity?

There are a couple of different types of dehumidifier, one is more suited for use in colder temperatures, as it has a heating element. However they are more expensive to run.

Its because a dehumidifier works by creating a cold surface for condensation to form on, remember that is how condensation is created. Therefore if its cold and you make water colder if goes solid and it then has trouble dripping out of the pipe.

Thanks; I wondered if it was to do with the amount of moisture in the air changing with temperature.

Mine's a Meaco and has a defrost option. I just dug out the instructions and it says not recommended below 5C.

[b14]

I'd bet it's probably 65% humidity outside as well, if it's a drafty Victorian house - just heat it to where you want it to be and don't worry about humidity. A dehumidifier can't really get a handle on the inside air if it's constantly being changed for similarly damp air from outside.

[Mr Whippy]

I run a bunch of SwitchBot humidity/temp sensors. It’s interesting seeing the outside change vs the inside, and loft etc.

Our current house had a lot of humidity in it initially but I ran a meaco Arete 2 from early on and it slowly calmed down so it’s only on half the time now.

I think the fabric of the house just dries out over weeks and then stabilises.

Set at 55 RH.


We still get some condensation on windows, there is no getting away from it if an interior surface gets very cold.


Yes get PIV, assuming you have trickle/venting.

[Mabbs9]

b14 said:

I'd bet it's probably 65% humidity outside as well, if it's a drafty Victorian house - just heat it to where you want it to be and don't worry about humidity. A dehumidifier can't really get a handle on the inside air if it's constantly being changed for similarly damp air from outside.

I think this is easily overlooked. Water collected doesn't really reflect on a house being damp unless it happens to be totally air-tight. Which of course it isn't.