Humidity in the House....Talk to me!

[Mysterae_]

You said “get a roofer to ventilate it” in the hope it will help.

He is saying “look outside, it can’t get more ventilated and it’ll still have moss and mould when wet”

My theory is that the warm air from your home is getting through the ceiling in your house to the roof and it’s trapped there. Ventilation will help, both in summer and winter, but I would look into whether you are getting condensation in the roof. If it’s dry on the walls and beams then it will be fine. If it’s wet then it’s time to do something.

I see, thanks for the explanation, @GeX has a good point, you can't get more ventilated than grass in the open. But the dew on the grass field will evaporate, in an enclosed space not so well without ventilation?

There is evidence of mould beginning on roof from last winter, which was a trigger for working on the loft in the first place. Yes, it's almost impossible to stop warm air entering the loft from the ceiling - through the ceiling plasterboard (unless foil backed), the holes where the cables for lights are, the loft hatch are amongst the few culprits.

 

[Grim5]

House humidity should be 45-60 max for comfort and health. My old Victorian terrace sits around 55-60 with no special arrangements.

probably because either you live in a low humidity climate, or because your house is so old, it's poorly sealed and new air from outside is constantly blowing inside, which removes moisture that was inside the house

 

[Grim5]

There's no way we get anywhere near that in our modern homes with no open fire use and sealed up windows.

Ventilation systems can, if setup correctly they can replace all the air 1 to 3 times per hour

 

[Grim5]

I'm in a similar situation with the two lofts at each end of our property. Current Tapo readings are ~14ºC and 76% humidity. I was thinking about investing in a little dehumidifier with a 12L tank for both. Then just having Tapo control the on/off with a range %. But is it worth it for a loft? One of the two lofts has no windows and no ventilation. I have a nest thermostat in the main hallway and it is reporting 20ºC indoors and 64% humidity.

You probably want to add some heating, while it will still work, dehumidifiers won't operate efficiently at 14c, you'll want to get that temp up to 19/20 and then the dehumidifier will do a better job and use less power. That's only if you care enough, its only a loft anyway

 

[Gammawolf]

You probably want to add some heating, while it will still work, dehumidifiers won't operate efficiently at 14c, you'll want to get that temp up to 19/20 and then the dehumidifier will do a better job and use less power. That's only if you care enough, its only a loft anyway

Thats not quite true of desiccant dehumidifiers..

 

[Grim5]

Thats not quite true of desiccant dehumidifiers..

True, forgot about those, I've never used those before, mine are all compressor condenser units - went with this because I tend to run them more in hot weather

 

[danlightbulb]

Here's the kind of nonsense I have to deal with.

How can it possibly be the same humidity outside at 12 degrees as it is inside at 20 degrees. There's nothing in the house generating this moisture apart from me and the house was ventilated this morning.

 

[mattyfez]

Here's the kind of nonsense I have to deal with.

How can it possibly be the same humidity outside at 12 degrees as it is inside at 20 degrees. There's nothing in the house generating this moisture apart from me and the house was ventilated this morning.

Lower your inside temp by 1 or 2 degree and see how you go.
It's relative humidity and warmer air holds more moisture.

 

[b0rn2sk8]

Lower your inside temp by 1 or 2 degree and see how you go.
It's relative humidity and warmer air holds more moisture.

If you lower the temperature, the RH will increase - its the opposite of what want to do. The only way to get rid of it is ventilation or a dehumidifier, warmer inside will help with ventilation as it naturally wants to escape and cooler fresher air is drawn in.

How can it possibly be the same humidity outside at 12 degrees as it is inside at 20 degrees. There's nothing in the house generating this moisture apart from me and the house was ventilated this morning.

A human puts out a huge amount of moisture just breathing, that is before considering showering, cooking etc.

Even if you run a dehumidifier, it will take a long time to lower it as it will be pulling moisture out of the fabric of the building. If you are not getting mould or condensation issues, its probably fine.

 

[dlockers]

Are there PIVs that are DIYable?

 

[b0rn2sk8]

Are there PIVs that are DIYable?

They all should be, its just a fan slowly blowing air through a hole in the ceiling.

Think installing an extractor fan, the other way round.

MVHR is a very different beast.

 

[dlockers]

I think that's what I may have had in mind (and assumed not really DIYable).

Are Dehumidifiers effective on top of things? I have a small space on top of a ~5ft wardrobe.

 

[b0rn2sk8]

Yes, although you need to think about emptying it fairly regularly and if you get the version which uses a compressor, you might not want that on top of a hollow box (noise reverb).

It probably goes without saying that you shouldn't need both PIV and a dehumidifier.

 

[jonneymendoza]

If you lower the temperature, the RH will increase - its the opposite of what want to do. The only way to get rid of it is ventilation or a dehumidifier, warmer inside will help with ventilation as it naturally wants to escape and cooler fresher air is drawn in.




A human puts out a huge amount of moisture just breathing, that is before considering showering, cooking etc.

Even if you run a dehumidifier, it will take a long time to lower it as it will be pulling moisture out of the fabric of the building. If you are not getting mould or condensation issues, its probably fine.

So I'm currently away from home and my humidity in my vacant place is hovering around 70 percent...

This is with heater off but with frost protection and my rooms are a cool 11 to 12 degrees.

 

[b0rn2sk8]

So I'm currently away from home and my humidity in my vacant place is hovering around 70 percent...

This is with heater off but with frost protection and my rooms are a cool 11 to 12 degrees.

The relative humidity will drop as soon as the air warms up as its capacity to hold water will increase and the same amount of moisture in the air will remain.

 

[jonneymendoza]

The relative humidity will drop as soon as the air warms up as its capacity to hold water will increase and the same amount of moisture in the air will remain.

So should I keep the heater on whilst I'm away?

 

[danlightbulb]

Are there PIVs that are DIYable?

I have been considering these myself for some time. The two brands are Nuaire Drimaster and Vent Axia Pure Air. They are around £4-600.

The issue I have with them is no smart/remote control. In this day and age I'd expect to be able to remotely schedule the unit, change settings and activate/deactivate/schedule the heater element.

 

[b0rn2sk8]

Not sure I’d ever bother with the heated versions. use your central heating, it will be cheaper.

Likewise, I would t get one unless you actually have issues with condensation.

So should I keep the heater on whilst I'm away?

Frost protection is fine.

The humidity itself isn’t a problem, it’s when very warm and moist air (like say from your breath) condenses on cool surfaces, that’s when you get mould.

If nothing is in the house producing moisture, you aren’t going to get damp.

 

[danlightbulb]

Not sure I’d ever bother with the heated versions. use your central heating, it will be cheaper.

Likewise, I would t get one unless you actually have issues with condensation.

Which is why I wanted smart app control. Could schedule the heater to come on only when I get the cheap overnight electricity. And could turn the unit off completely if it's really cold out.

It should be much more effective than the dehumidifier but I'm worried it will make the house colder / increase heating costs.

 

[b0rn2sk8]

Which is why I wanted smart app control. Could schedule the heater to come on only when I get the cheap overnight electricity. And could turn the unit off completely if it's really cold out.

It should be much more effective than the dehumidifier but I'm worried it will make the house colder / increase heating costs.

It will be cheaper to run than a de-humidifier but only if you ignore heating costs. It's essentially a high static pressure fan and its objective is to increase air changes in the property, more air changes = more heating needed. You could just run it off a smart plug rather than hard wiring it in.

You could also just run the de-humidifier overnight on the cheap rate power and you'd hardly notice it on your energy bill.