Dehumidifiers and Window Condensation

[Me!]

After a few cold nights a couple of weeks ago the condensation started streaming off our upstairs windows overnight and pooling at the bottom as it does every year about this time.
Our downstairs windows are secondary glazed and don't suffer the same problem, and despite being a five bedroom house, because of the way the 1st floor is divided into two parts it means the condensation is only really a problem on one upstairs landing and the two bedrooms and bathroom that come off it.
So, I have upgraded the bathroom extractor fan to one of these and set the timer to run on for half an hour after a shower.
And I have also bought an Ebac Homedry 12L dehumidifier which has now been running for 10 days in its Automatic "Smart High" mode just by the bathroom door, and is now extracting about 1 litre of water per day.
Last night, the first cold one in a while, the external temperature was down to about 3 degrees C and this morning in the bathroom (before any showers) the temperature was 19 degrees C, the RH was 51% and the condensation on the windows was bad enough to be dribbling down off the bottom of the glass again.

Which brings me to my questions to any of you who have dehumidifier experience, particularly with Ebac, and they are -
- What sort of level of RH% do I need to get down to so as not to get condensation pooling at the bottoms of windows with a 19C internal temperature and an external down to about zero?
- Should an Ebac on Smart mode eventually get down to whatever that required level is or should I be using the Boost mode?
- Does anybody know exactly what levels an Ebac Smart mode is detecting and more importantly what it is aiming for as a target?

Many thanks.

 

[88v8]

Unhelpful musings...

Our Ebac 2650 (two off) run on Auto. They seem to reduce the rh by about ten points. So, whatever it would have been, minus ten.

Each fills its gallon container in 2-3 days, so about the same as yours.

Our rh varies greatly by room. Where I'm sitting, in the cold timber frame about the kitchen, its 62F and 68%.
Overall I'd say we're around 60%. By the spring it will be around 45%. In the cellar where one of the Ebacs lives, perhaps ten points higher.

Lighting the fire(s) has a greatest effect; for example, last night we lit the stove in the sitting room for only the third time this winter, and overnight the rh in that room fell from 63% to 57%.
But this morning, with the internal temp at 64F, its (north facing Critall) was still moderately wet.

The worst window is the Critall in the kitchen. The kitchen is cold. Timber frame on three sides, some original wattle no insulation, north facing. Despite assiduous use of a powerful extractor, that window runs with water every morning, I vacuum it off.

Here, the cottage is inherently damp. No dpc no dpm. yes it can breathe, but every day there is a volume of damp that has to be dissipated, and some of it condenses out on the window, and on a couple of cold spots on the wall that grow mould.
PO obsessively coated the upstairs walls and ceiling with plastic paint. Incl the cold room where I'm sitting, the one with the mould. I look at the paint and sigh. A horrible job to remove it all from the wonky surfaces where it can't be scraped off. They were not really stupid people, he was/is a nuclear physicist, but oh dear.

Contrast our previous house, 1920, dpc and suspended floor. Opposite problem. Too dry. Rh never above 50%, then in the winter down to 30% which is bad for antique furniture. Temperature, lower = heated to around 62F, higher when we lit the fire(s). But no condensation anywhere.

Notably, there were four open flues - sitting room, 2 x bedroom, bathroom, that must help.
Whereas here in the cottage we have just two stoves and although the dampers are open all the time , I bet not much air goes up there when they are not alight.

So I think it has a lot do with firstly the volume of moisture in the house and secondarily how well it is routinely extracted. But then that brings us back to rh.

None of which really helps you.
Those particular windows you mention must be cold. What constitutes too cold, dunno.
In general, the solution is more ventilation. Brrr! And the dilemma that open windows defeat the dehumidifier.

A dew point calculator here https://inspectapedia.com/Energy/Dew_Point_Calculation.php Not only a period property problem.

There. All that wasn't very helpful.

Ivor

 

[a twig]

With regards to Ebac, I'd personally have gone for one of their heftier commercial jobs (yellow bodied).

We have one in our cellar that keeps it at a constant 53% RH all year round despite water sometimes coming up through the floor and puddling after heavy rainfall. The outlet hose of ours runs outside into the gutter downpipe with the aid of a separate condensate pump. It runs 18 hours or so a day during winter on nearly maximum setting.

The easier solution is to reduce the temperature differential if possible, and that will reduce the problem, can you squeeze in some secondary glazing/film?

 

[Me!]

Many thanks for the replies, musings or otherwise

I'd certainly never heard of a psychrometric chart before. They are not the easiest things in the world to read, but if i've understood it correctly, then I would need to get down to an RH of about 20% in a room at 19 degrees C to have a decent chance of stopping the condensation on the window, ... and 20% is never going to be achievable or even desirable for other reasons.

I was concerned that I may have bought a dehumidifier that wasn't powerful enough, and that is why i mentioned the layout of the house. When first plugged in and set to Smart mode, it ran almost continuously for the first 48 hours. However, now after a couple of weeks and with a room RH% in the low 50's, the Ebac controller spends more time with the compressor off than on so it seems to have got to whatever parameters it is aiming for.

It does appear though that even my new upgraded extractor fan is still not really up to the job. I've just been told by a Building Services Engineer that allowing for ducting losses I should get a fan that provides about double the flow rate of even my new one. And that new one is already about four times the rate of the one I've just replaced that has been there for the last 15 years! I've asked for a quote for another new fan :roll:

So, reducing the temperature difference at the window does seem to be the way to go. I had already been thinking of adding some internal wooden shutters to the bathroom window, but I'm now following Feltwell's Glass Shutters topic with interest to see if that is an option for me.

 

[Feltwell]

I had already been thinking of adding some internal wooden shutters to the bathroom window, but I'm now following Feltwell's Glass Shutters topic with interest to see if that is an option for me.

The glass shutters on that website sit inside the staff beads - so actually they could be used as well as wooden shutters.

I stayed at a gorgeous B&B in an old Scottish manor house this week (a very rare work stayover perk!), they had original wooden shutters throughout that fold back into a recess in the angled reveal to look like panelling - I was very jealous!!

 

[CliffordPope]

It does appear though that even my new upgraded extractor fan is still not really up to the job. I've just been told by a Building Services Engineer that allowing for ducting losses I should get a fan that provides about double the flow rate of even my new one. And that new one is already about four times the rate of the one I've just replaced that has been there for the last 15 years!

There's a price to pay though for a powerful extractor fan, and that is the draught.

Mounting a very powerful fan just above your head in the shower certainly removes the moisture at source, but at the cost of turning a warm relaxing experience into something like standing under a waterfall in a cold winter. The hotter you make the bathroom to try to compensate the faster you pump all the warmth outside

 

[tobydog]

When we first moved into our thatched and timber framed cottage we seemed to be overwhelmed with condensation. We fitted better fans and fixed most of the damp issues, and purchased a dehumidifier but, at this time of year, I was still using no end of kitchen towel and rags to soak up the window puddles in the mornings. I then noticed that by December, as the air outside cooled and dried, it wasn't anywhere near as bad, especially on some very cold crispy mornings. I accepted that we were never going to solve the soggy October and November but this was made so much more bearable when we bought a Karcher Window Vac which enables me to clear the whole house (if necessary) in 10 minutes. December onwards seems to help start drying the house out if it's cold enough and this can be helped when we get the wood burner going. I realise this doesn't help solve everyone's problems but it made me hate our single glazing so much less.

 

[Me!]

Unfortunately our worst windows for condensation are leaded glass with small diamond panes, so I can't see that a window vac would work very well on them.
If anyone has tried then I'd love to hear how successful it is?

 

[88v8]

I've just done the morning vacuum of our leaded lights with the Karcher. Five years or so ago, I took the small tool and cut one end off it, so the blade now is 5" across, and that fits our leads, albeit they are oblong rather than diamond.
The cut end I sealed up with ductape as a temporary measure, hmm yes that was around five years ago.

Indeed, the condensation is worse in the autumn, before the woodburners have dried the house.

Fan... ventilation. No point fitting a big fan, if the air can't get in.
We all know the temptation to seal up the windows and doors with draught strip. But if we called it ventilation sabotage strip, perhaps we would be less inclined.
The simple fact is that for a fan - or a chimney - to pull air out, the same amount of air has to get in.

The most pleasant way is for the air to percolate around all the gaps at the perimeter of the original doors n windows. Then we hardly notice it, because the ventilation is distributed all around the house.

If everything is sealed, how is the air to get in??? Down the chimney? Does your bathroom have a chimney?

Currently I am decorating a room. It has new windows, they were supposed to be like-for-like replicas, from a conservation joiner. And so they are, but they came with plastic seals. We had a 'conversation' about this, he mumbled about FENSA. Now, I don't give a flying f*** about FENSA, and I'm annoyed that I have the task next year of eliminating the seals and replacing them with strips of wood glued in to reinstate the 'draughts'.

At the moment, because I'm painting the windows, the seals are out so there is an eighth gap around the perimeter. And you know what, the windows are dry as a bone. Despite which, the temp in there is adequate for working and the heating is maintaining 58F (fifty eight) without working hard.

So, on the whole, once one has eliminated or minimised any damp issues, the answer to condensation is less heat and more ventilation.
Wear a woolly.

Ivor

 

[a twig]

Well, our bedroom has a fireplace with a 10" square chimney.

We don't over heat it as the room has its own thermostat and doesn't get above 16°C, there's a solid draught across the room from the badly fitted door and we still get condensation on the panes of our double glazed windows and even mould on some of the stonework....

My only thinking is that I haven't finished stripping the old masonry paint from the outside of the bath stone walls, and that is keeping the walls cold and damp, leading to condensation, otherwise I'm stuck for ideas...

 

[CliffordPope]

So, on the whole, once one has eliminated or minimised any damp issues, the answer to condensation is less heat and more ventilation.
Wear a woolly.

Ivor

Then after you have had your bath or shower you have to dry out the sodden wooly somewhere?

 

[Feltwell]

How do we all survive? After all:-

Risks of adverse health effects arise when indoor temperature drops below 19C, with serious health risks occurring below 16C, the guidance says.

https://www.bbc.co.uk/news/uk-50294404

It's a wonder none of us are dead already :roll:

 

[88v8]

Well, our bedroom has a fireplace with a 10" square chimney.
We don't over heat it as the room has its own thermostat and doesn't get above 16°C, there's a solid draught across the room from the badly fitted door....

Hmm, do you have a hot water bottle?

But seriously folks, that draught under the door is internal air.
Ventilation requires external air.
Presumably none is coming through your dg windows, so how does fresh air get into the room and indeed into the house?

Mould on stonework, yes we had some of that in the sitting room where water runs off the northerly Critalls. Much less so since I shortened the legs of the storage heater so I could put it under the window. In fact, now I think about it, I'm not sure the mould is there at all.
And that's the room where we removed the cement pointing, it does seem to have made a big difference to the feel of the room, so you could be right about the residual damp in your walls.

What RH do you have?

Ivor

 

[88v8]

Then after you have had your bath or shower you have to dry out the sodden wooly somewhere?

It's very efficient. At the end of my bath, I add a spoonful of soap flakes then I roll over a couple of times so that's the wash cycle, then I hang it outside until it rains and does the 'rinse'.
As regards 'delicates' which require a less robust washing, I put them on my head and just dunk them in once or twice.

The drying can be an issue, I really need a lean-to, but I have plenty of spare woollies which I share with the moths.

All this accrues a significant saving in electricity as compared to the washing machine.
Saving the planet little by little.

Ivor

 

[tobydog]

Me! - even though you have diamond leaded light windows, the Karcher Window Vac may still be worth getting. The blades (you get two sizes) are fairly flexible and could help remove some of the water. Even if it just acted like a squeegee, it's great for sucking up all the water from the window sill rather than using towels.

 

[a twig]

Well, our bedroom has a fireplace with a 10" square chimney.
We don't over heat it as the room has its own thermostat and doesn't get above 16°C, there's a solid draught across the room from the badly fitted door....

Hmm, do you have a hot water bottle?

But seriously folks, that draught under the door is internal air.
Ventilation requires external air.
Presumably none is coming through your dg windows, so how does fresh air get into the room and indeed into the house?

Mould on stonework, yes we had some of that in the sitting room where water runs off the northerly Critalls. Much less so since I shortened the legs of the storage heater so I could put it under the window. In fact, now I think about it, I'm not sure the mould is there at all.
And that's the room where we removed the cement pointing, it does seem to have made a big difference to the feel of the room, so you could be right about the residual damp in your walls.

What RH do you have?

Ivor

Currently 55% - fresh air enters through the front door (in the next room to the bedroom), and through the 3 open fireplaces round the rest of the house.

The other thing I'm considering is that there are no trickle vents in the window frames, so I'm toying with adding some...

 

[a twig]

Replying to myself - "who said that?"

Anyway, three trickle vents ordered, will install next week, clean off all the mould and then see what happens!

 

[88v8]

Currently 55% - fresh air enters through the front door (in the next room to the bedroom), and through the 3 open fireplaces round the rest of the house.

55% RH should be OK.

I was being slightly facetious when I suggested that fresh air could enter via open fireplaces. If the chimneys are so ineffective that they permit air to be pulled down them, that is not very good.
And can lead to orrible sooty smells.

Air into a specific room can of course be influenced by whether the door is usually shut or open, and how well it seals.

Easy to ascertain where air is coming from, if at all, with the aid of a thin strip of tissue paper or the flame of a candle,

I've never tried trickle vents. Can't do any harm.

Ivor

 

[Flyfisher]

If the chimneys are so ineffective that they permit air to be pulled down them, that is not very good.
And can lead to orrible sooty smells.

Yes. Chimney reversal.

We used to live in a wood so the house was largely shaded during the summer, which was nice as it was always cool on very hot days. But during the summer months the warmer outside air and cooler indoor air often resulted in our chimney 'reversing', resulting in 'orrible sooty smells'. We fixed the problem by fitting a 'chimney balloon' during the summer months. https://www.chimneyballoon.co.uk/

When the fire lighting season arrived we simply removed the balloon and used the chimney as normal and there was never any reversal problem until the following year. The first fire of the season could be tricky as the chimney contained a 'plug' of cold air and sometimes our open fire would smoke heavily before the chimney got itself working properly. We learned that a few sheets of lighted newspaper stuffed up the chimney was enough to push out the 'plug' of cold air, whereupon the fire would light easily with no smoked spilled out. With regular fires throughout the winter the chimney retained enough residual heat such that it never 'reversed' during the winter. When the fire lighting season ended we had the chimney swept and then reinserted the baloon until the following winter.

Chimneys can be quirky things and it can take a while to fully understand their eccentricities.

 

[LeeL82]

I had already been thinking of adding some internal wooden shutters to the bathroom window, but I'm now following Feltwell's Glass Shutters topic with interest to see if that is an option for me.

The glass shutters on that website sit inside the staff beads - so actually they could be used as well as wooden shutters.

I stayed at a gorgeous B&B in an old Scottish manor house this week (a very rare work stayover perk!), they had original wooden shutters throughout that fold back into a recess in the angled reveal to look like panelling - I was very jealous!!

Not a manor house, but our bedroom windows (in scotland) recess in to look like paneling, the fold out to cover the windows, I thought they all done this?