Now that the temperature outside has dropped, the windows start to accumulate water vapor. I am assuming that it might also lead to that black stuff forming. Is there a more efficient way of dealing with the condensate than wiping it dry every day?
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S T O ẞ L Ü F T E N T T O O ẞ ẞ L L Ü Ü F F T T E E N NBonus points for creative styling
You have to adopt the concept of “stosslüften” to get rid of excess humidity in your room. Warmer air carries more water, but it condenses on cooler surfaces Like outside Walls or Windows, the Window is the better Option because wet Walls get moldy soon. You also should make shure that there are no big furniture or other items without space to an outside wall if the building ist Not well insulated.
The issue is that you typically don’t have any excess humidity in winter. Health wise you want 40 to 60 (or 50 to 60, depends on the source) percent humidity are ideal and with a lot of ventilation you’ll quickly drop below that. Hence you might actually want to think about adding more humidity to the air (e.g. with plants or a humidifier).
You’re definitely right about walls though.
If you have condensation issues, you definitely don’t need to add more water to your air
Get a swamp cooler. They are cheap and effective. You can also makeshift one by putting a wet towel in front of a fan. And get a humidity meter they cost like 4$.
Or just dry your clothes on a rack indoors…
Couldn’t solve this as well so far. Looking at it with a thermal camera in cold weather revealed insufficiently insulated windows as the root cause. Basically the frame holding the glass sandwich itself is thermally too conductive at the seam, which tends to be a lot colder than the rest. If the difference is too low, condensations forms depending on the current dew point in your room. As a rule of thumb, if you have 22°C inside and 59% relative humidity, you have a dew point of around 14°C. If your insulation on the windows gets below that, humidity condensates there first. Airing out the room can help lower the dew point, but usually that’s barely enough.
The only fixes to lower the dew point are reducing relative humidity to inhumane levels (below 30% relative) or increasing the room temperature by alot (more than 25°C), all combined with several airing out of the room for 5 minutes 3x daily all winter.
Other things to do are identifying and monitoring high-humidity rooms nearby. Most likely your bath with a shower inside. If you have a “dark bathroom”, meaning now windows and just a vent, switch the vent for a humidity-controlled version and dial it in on around 63% humidity. Install a vent in the door near the bottom as well if not existent already, since a closed door chokes the vent. Once the door opens, water vapor enters the flat/house and raises the humidity quickly.
The only ultimate solution to this is replacing the entire windows with three-panel versions in properly insulated frames, reducing constant water vapor sources like in baths and kitchens using whatever venting methods work best there and lastly (most likely impossible due to cost if you are not considering building a new house) switch from traditional radiation heaters to an air conditioning heating/cooling solution which levels out most of the humidity issues electrically.
This is a detailed answer with which I largely agree, I just want to point out that the installation of better insulated windows shifts the problem in insufficiently insulated buildings to other areas, often the moisture then settles in corners and leads to mould there - in the past it was said that the window should always be the coldest surface in the room, today there are Ventilation, insulation,… but i think this is still a good rule
Basically the frame holding the glass sandwich itself is thermally too conductive at the seam
Could it be, that the seals have aged and don’t seal as well anymore? A constant draft through there would probably lead to a cold frame as well.
Interesting idea. The thermo cam shows a consistent stripe of cool area where the seal sits all around the window. Not sure…
Easiest way to find out: Get some TesaMoll in the right size and try it out on one window.
Ah, my bad. I meant the silicone sealant of the glass pane where it meets the frame. The regular seal - while originally bad - has been fixed already. So it’s really the seal where the glass pane meets the movable window frame, not where the movable frame meets the frame fixed to the walls, if that makes sense.
Yeah, makes sense. That would be unusual. Only thing I could imagine is water entry into the frame, if the outside seal on the glass was bad. The part we can see in the picture looks alright though.
Usually, it’s one of those two white seals that lose proper contact with their counterpart surfaces, either because the wood deforms irregularily (and thus gets bend) or because the whole moving frame needs to be readjusted to close tighter. Bit weird in your case, as you say they are fine. How is the temperature in the middle of the pane?
A picture should explain this better. Middle of the pane is difficult to measure in Infrared, but a regular probe taped to it shows about 18°C right now, so just a bit below room temperature. I assumed this behaviour is normal, since all windows in my rental are like this. Note that this windows specifically has not been resealed at the movable part of the frame yet. However, as you can see, it’s not the coldest point of the entire window either. Outside temperature was -3°C when the photo was taken.
It doesn’t seem, that the movable part of the frame is even that cold. From the scale I’d estimate it at 17°C or so? It really seems that the contact between the frame and the pane is the weak point.
For comparison, I’ve just gone and measured my relatively new windows, about 3 years old, plastic frame. Its -3°C outside as well.
I’ve measured my pane temps by sticking a bit of matte tape to it:
The pane is about 3°C colder than the ceiling and the floor:
In my case, the coldest part is the fixed part of the frame:
The contact area between the pane and the frame doesn’t cool off nearly as much as it does in your case. I guess, that’s your answer regarding the condensation. Not much you can do about that, it seems :/
EDIT: Yeah, I think that is it. Just had a look at how the panes are fitted into my windows: The plastic frame overlaps them AND the pane edges aren’t metal or at least the metal is covered. In your case, the metal frame is isolated from the inside and the outside basically just by a bit of silicone. That’s probably what makes this heat bridge a lot less critical in my case.
Thank you so much for a quality answer!
The black stuff is mold and it’s both, a health hazard and it eats away the gasket.
It’s best practise to keep temperatures at least at about 16° C at a relative humidity of at most ca. 60%. So set your heater in the room accordingly. Possibly you need to go a few degree higher. A thermohygrometer can help to keep an eye on the temperature and humidity. If the humidity rises above 60%, it’s a good time to open the windows to get rid of excess humidty in the air. (
That does work of course if it’s rainy outside, i.e. even more humid.See correction in comments by @Mrs_deWinter.) For air quality resons, ventilating rooms a couple of times per day is a good idea anyway.You can find more resources on that topic if you search for mold prevention in residental buildings.
Edit: Striked an incorrect statement, referred to correction.
(That doesn’t work of course if it’s rainy outside, i.e. even more humid.)
It works even if it’s rainy outside. The relevant factor is temperature. Warm air traps much more humidity than the cold air outside - even if it might feel humid there. When we open the windows our saturated warm air gehts switched with saturated cold air, which then warms up inside and increases it’s capacity to absorb humidity in turn.
As long as it’s colder outside than inside ventilation will get rid of a room’s humidity.
5-10 minutes is perfect: It allows for a significant air change and doesn’t cool down the room (floor, walls, furniture) too much, so as soon as you close the windows again the temperature can quickly rise and allow for the desired dehumidification.
Thanks for the correction. :)
temperatures at least at about 16° C
Which should be 2 on thermostats
That is, if the heating system is corrctly sized for the space your heating and adjusted to current weather.
Thank you, I did get the thermo/hygro-meters in all the rooms. We try to keep the temperature at about 20-21C, but the humidity is definitely on the high end, around 65%
Thank you for the suggestions!
Wipe it off in the mornings - Lüften alone will not prevent mold on the window frames. Lüften short and intensive several times a day.
That’s what I do right now. But it gets annoying af)
Move to a warmer climate where that doesn’t happen? Or wait what’s in the climate catastrophe lottery for Germany - it may become much warmer in the future (not necessarily, depends on Golfstrom).
The other solutions (air dryer and the likes) are more annoying and much more expensive. It simply is the way it is.
Stoßlüften.
Please measure the room temperature, humidity in the room as well as the temperatures of the frame, the surrounding walls and the glass. A simple IR thermometer and a cheap digital hygrometer suffice, stick some matte tape to the glass to measure that. Find out, what the dew point is and how far below that the critical surfaces are.
As a reference: I currently have 23°C room temp, 40% rel humidity, the walls are at about 22°C and the window frames here show at 19°C. No condensation, because the dew point is well below all of that.
Thank you for the suggestion. My hygrometer shows 65% at about 20C. But the humidity outside right now is like 90% with all the snow and rain. So I guess part of the problem might be that the room is too cold.
See the thing is, humidity is always given relative to the Dew Point in percent. If I assume 0°C for outside with 90% humidity thats 4.6 g/m3 of water. In your room with 20°C and 65% humidity its 11.2347 g/m3
So if you open your windows your humidity will decrease. Warmer air can store more water.
Under ideal conditions you could get to 27% at 20°C which you will never reach, but opening the windows for 5 minutes (ideally two windows on opposing sides of the house to get a good draft) should get you below 55% already. Repeat it three time a day and you will stay below 50% humidity.
Also, thanks for the detailed calculations. I never realized how that actually worked
Glad to help :)
I forgot to mention: Thats also why you get condensation on windows. The window is cold and cools the air near it. The air than can hold less humidity and it condensates on the window.
If you measure the temperature of the coldest spots on your windows you could even calculate how much humidity you can have in you flat at 20°C before water condensates there.
I’m kind of shuddering at the thought of opening my windows in this cold, but ok, I’ll try that)
There’s fan systems that take outside air and inside air and pass them by each other in a heat exchanger. I’ve got a few of those in my house, the UI looks like this and this explains the principle quite well I think:
Maybe your landlord is open to the idea to install one of these. You get permanently fresh air without losing too much heat, they get some peace of mind that there’ll be no mold in their property.
Thank you for the tip! Our windows do have two “ventilation things” on each side that move air in and out. I am assuming they kind of do what the picture shows.
Eh, not too likely if they go directly into the wall. The trick with the one I’ve mentioned above is the heat exchanger. The warm air from inside passes its heat to the cold air from outside without touching it directly. The water it loses during that runs to the outside pipe and drips off.
Ah, ok. The ones we have are embedded into the walls. I had a feeling they were just a gimmick)
So I guess part of the problem might be that the room is too cold.
Not the room, but certainly some surfaces. at 65%/20°C the dew point is at about 13°C. Any surface near or below that temperature will collect water droplets. Find those, measure them and then either find a way to get these surfaces warmer or lower the humidity in your room until they are no longer beneath the dew point. If necessary, get an electric dehumidifier. Unless you need to run it all the time, it’s a valid workaround for a few days per year.
Just checked the windows temperatures. Interestingly, the temperature varies quite a bit along the surface of the window. The middle of the window is about 18C but the bottom measures at about 13C, which is exactly the dew point for my 20C / 65% (thanks for the calculator, btw).
Thanks so much for a detailed answer, I will try to follow your advice.
I’d suggest using a dehumidifier. Alternatively open the windows once or twice a day to reduce the humidity in the room where this is happening.
Dont use a dehumidifier. Just open the windows to let humid air out and fresh air in.
A dehumidifier can help a lot when the room is barely heated. This is also the case when insulation of the building is bad. Some apartments will always be humid, even when opening the windows everyday. In those cases a dehumidifier will do the trick and you’ll get about 2 - 3liters of water out of the room within a couple of hours.
That makes sense if you want to ventilate their air anyway. After all you need to get rid of CO2 inside as well. Fun fact: You don’t need to worry about the lack of oxygen in that context. If the oxygen level have dropped from from the normal 21% do 17% because the oxygen (O2) was magically removed you’ll still be perfectly fine. But if those were converted into 4% CO2 that will make you sick.
Anyway: My point is that a dehumidifier is more often more efficient because it doesn’t involve wasting warm air. It’s also a fairly efficient heater. Dehumidifying, i.e. turning vapor into liquid means that you get the energy used for evaporation back. It’s essentially sweating in reverse. With a typical dehumidifier that means you get about 2 Joules of heat for every Joule of electricity used.
Haven’t considered a dehumidifier, I was only aware of humidifiers, I’ll check it out
I’m not sure if it’s a product in Germany, but in the US we have plastic sheeting that you tape to a window and use a hair dryer to shrink it to a tight fit. This would increase insulation and might help reduce or eliminate the condensation.
Something like this as an example: https://www.harborfreight.com/heavy-duty-window-insulation-kit-59241.html
Interesting product! Only catch I see is that if applied now the risk of trapping moisture between the glass and the plastic is high. Leading to condensation you can’t remove/dry.
On top of that the window is a 3 pane glass. Pretty much top notch. Don’t think the plastic wrap could solve the problem. I’ll sure try it in my cabin tho!
If the window is triple paned and still getting condensation regularly maybe the seal is bad on the window?
Or maybe there is too much humidity? Sometimes our kitchen windows do this in the winter when we cook a lot.
The second one. A bad seal will manifest differently and in another part of the window (where the windows itself meet the frame
Not sure if they gave a whole home humidifier but if they do, turning that down could help too. But it’s a balance of personal comfort and condensation then.
Hi there, I also had this issue and asked an HVAC technician about it when he was here last. I understand in Europe forced air heating isn’t very common, so this might not work for you (I’m in Pennsylvania). My issue was that the humidifier on my furnace was turned up too high, simple fix, I just couldn’t find the adjustment knob as it was mounted really high in the ceiling.
Yeah, heating is mostly done through the radiator heaters or heated floors around here.
If you cannot afford to replace the windows then look into adding storm windows. This is simply another window added to the outside of your window that adds another layer of insulation. Usually this increases the insulation enough to stop condensation.
These are common in the US. IDK how common they are in Europe.
This might be bad advice depending on the insulation of the outer walls. If you increase the insulation on these windows, the water might still condensate, but this time on your walls where you cannot see it or wipe it away. A rule of thumb is to insulate the outer walls better than the windows.
Yep, this. This is also extremely important to keep in mind when retrofitting triple pane windows in older houses. Moving the condensation to the walls doesn’t do you any favors, in that case you’d have to add isolation to the walls as well.
And that’s how we got mould this year 🙌 Hopefully the owner will isolate the walls next year…
I wouldn’t wait until they get moving. I’d try to find an agreement with them, where I’d pay for a dehumidifier and have them pay the electricity for that or something along those lines. Mold is directly bad for your health but also for their property value.
These are common in the US. IDK how common they are in Europe.
We have roller shutters. . Way better. Those obviously block the light, but since it’s coldest at night and nights in winter are long they help a lot.
But, just like with storm windows it’s not necessarily allowed to add those due to zoning laws and landlords.
In any case, if you’re ready to spend money and alter your building, then just buy new windows. New windows in Europe typically have at least three panes and a metal layer against infrared.
Thanks, like someone else already mentioned, there are these outside shutters, which we do have
These windows need thicker glass that ensures better insulation.
That is triple pane already.
Yeah, sorry if that’s not very clearly shown on the picture, it is indeed a triple pane
