Condensation on aluminium window frames

[chris w]

'condensation has to go somewhere'

 

No it doesn't. The moisture can stay in the air. It only comes out of the air if a cold surface cools the air sufficiently to prevent that bit of air holding that amount of moisture. The loss of moisture from that bit of air is condensation.

 

If the air is not cooled to its "dew point", the air is quite happy holding the moisture. Hence, raising the temperature of a glass surface prevents condensation forming.

 

Clouds are formed by this process (not on a NB!!). The bottom of the cloud is the point where the "warm" air has risen to a point where the moisture starts condensing out due to its being cooled as it rises, and the top of the cloud is the point where all the moisture has condensed out.

 

Chris

[ChrisPy]

Under normal conditions, with equalised humidity inside and outside, good ventilation, etc. etc., you have the potential for a huge amount of condensation in the boat. About the same that you see on the wet grass at dawn most days. As Chris W implies, you have to warm all your exposed internal surfaces to avoid condensation. Alternatively you could dehumidify the whole boat using a lot of power, or drain away all that water before it does any damage.

[Roger Gunkel]

As has been said previously, moisture is going to condense on a very cold surface and unfortunately the windows and frames are directly connected to the outer shell so will stay cold. In modern houses, the frames are normally UPVC which is not a good heat or cold conductor so don't give the same problems, the glass is double glazed so the outer pane stays cold and the inner one warms up to room temperature and has no contact with the outer one. To replicate this in a boat you would need to stop the inner surface of the frame being in contact with the outer surface of the boat. Tom's idea with the wood strips achieves this, as does minerva's film double glazing. I tried Minerva's film last year with fantastic success. No condensation at all, and little heat loss through the windows. Bought it in Wilkinsons. The sticky residue from the tape came off with meths. This year I am trying to do the same with thin rigid acrylic sheet on a removeable lightweight wooden frame. It attaches to the wooden window surround and so the aluminium frame and glass is no longer in contact with the moist air in the boat. In the spring, or if you want to open a window, the whole thing just unclips in seconds.

I can't understand why simple double glazed windows with insulated frames for boats haven't been around for years. You wouldn't put metal framed single glazed frames in a house as anybody with experience of Crittall windows knows. Someone with a bit of business initiative could make a lot of money and keep boaters very happy. Are you reading this Gary?

Roger

[blackrose]

As has been said previously, moisture is going to condense on a very cold surface and unfortunately the windows and frames are directly connected to the outer shell so will stay cold. In modern houses, the frames are normally UPVC which is not a good heat or cold conductor so don't give the same problems, the glass is double glazed so the outer pane stays cold and the inner one warms up to room temperature and has no contact with the outer one. To replicate this in a boat you would need to stop the inner surface of the frame being in contact with the outer surface of the boat. Tom's idea with the wood strips achieves this, as does minerva's film double glazing. I tried Minerva's film last year with fantastic success. No condensation at all, and little heat loss through the windows. Bought it in Wilkinsons. The sticky residue from the tape came off with meths. This year I am trying to do the same with thin rigid acrylic sheet on a removeable lightweight wooden frame. It attaches to the wooden window surround and so the aluminium frame and glass is no longer in contact with the moist air in the boat. In the spring, or if you want to open a window, the whole thing just unclips in seconds.

I can't understand why simple double glazed windows with insulated frames for boats haven't been around for years. You wouldn't put metal framed single glazed frames in a house as anybody with experience of Crittall windows knows. Someone with a bit of business initiative could make a lot of money and keep boaters very happy. Are you reading this Gary?

Roger

 

Someone mentioned it was because a good double glazed window has a vacuum between the sheets (or at least moisture reduced air?) to prevent condensation inside. The problem that double glazed window manufacturers had on boat applications was that when you hit a lock wall the seals could break allowing in moist air, condensation and eventually mildew.

[tomandsophie]

A good friend of mine has fitted clear perspex over all his windows, simply screwing them into the wooden window surrounds. They completely stop all condensation and their boat is very warm even after the fire has gone out, whereas ours is cold very soon after the fire is out, with pretty much all the heat loss through the windows. I think I might have to do the same.

However, the brackets for the top hoppers stick out about 20mm past the wooden surrounds. My friend has got around this problem simply by filing them down. And, by the way, the job he has done looks very neat indeed.

My only problem with this idea is that I see our windows as a bit like sacrificial anodes for condensation! If there is moisture in the air (inevitable) I'd rather it went on the windows that condensed on our lining. To be honest, I don't care if the windows get covered in condensation as it runs down into the gutters and goes outside the boat. Fine. What I don't like is condensation on the frames dripping onto our lining and floor, although this is easily solved (as I wrote above) with strips of wood.

So I guess I just have to weigh up whether I want better heat retention or better condensation-protection.

[blackrose]

A good friend of mine has fitted clear perspex over all his windows, simply screwing them into the wooden window surrounds. They completely stop all condensation and their boat is very warm even after the fire has gone out, whereas ours is cold very soon after the fire is out, with pretty much all the heat loss through the windows. I think I might have to do the same.

However, the brackets for the top hoppers stick out about 20mm past the wooden surrounds. My friend has got around this problem simply by filing them down. And, by the way, the job he has done looks very neat indeed.

My only problem with this idea is that I see our windows as a bit like sacrificial anodes for condensation! If there is moisture in the air (inevitable) I'd rather it went on the windows that condensed on our lining. To be honest, I don't care if the windows get covered in condensation as it runs down into the gutters and goes outside the boat. Fine. What I don't like is condensation on the frames dripping onto our lining and floor, although this is easily solved (as I wrote above) with strips of wood.

So I guess I just have to weigh up whether I want better heat retention or better condensation-protection.

 

The only problem with that idea is that you can't open the windows. Sometimes it gets too hot in my boat and I want to let some heat out, but dount want to open doors or side hatches. Also when I put more coal on I often get fumes in the boat and I open the windows.

 

As far as the condensation goes, when I have used porthole bungs made out of foam (I only have portholes), and I have never found any condensation on the lining of the boat. There will always be a % of moisture in the air - it doesn't have to condense unless it meets a cold surface.

Edited January 31, 2007 by blackrose

[chris w]

Someone mentioned it was because a good double glazed window has a vacuum between the sheets (or at least moisture reduced air?) to prevent condensation inside.

 

The reason for having a vacuum is actually to prevent heat loss due to convection currents in the air between the two glass sheets. No air - no convection so any heat loss is due solely to conduction through the frame and radiation.

 

This is the same reason that foam is pumped into cavity walls, viz: to prevent convection currents. If you look up the insulating properties of air and foam, air is better! However, the effect of convection currents in the air negates this advantage in practice.

 

Chris

Edited January 31, 2007 by chris w

[blackrose]

The reason for having a vacuum is actually to prevent heat loss due to convection currents in the air between the two glass sheets. No air - no convection so any heat loss is due solely to conduction through the frame and radiation.

 

This is the same reason that foam is pumped into cavity walls, viz: to prevent convection currents. If you look up the insulating properties of air and foam, air is better! However, the effect of convection currents in the air negates this advantage in practice.

 

Chris

 

I meant condensation occuring between the panes which could also be a problem if there is no seal & no vacuum.

[Roger Gunkel]

I meant condensation occuring between the panes which could also be a problem if there is no seal & no vacuum.

 

I understood that there is no vaccuum in a double glazed window, merely moisture removal from the trapped air. A vaccuum would certainly give wonderful insulation but I understood was totally impractical due to the difficulty of greating a vaccuum and the resulting pressure of around 14lbs per square inch needing a huge thickness of glass. I have broken a few over the years and have never seen the explosive effect you would get with a vaccuum implosion.

I seem to remember that the ideal thermal separation for an air gap in a double glazed unit for minimum convection loss is about 20 mm. Over that and the insulation properties start to decrease because of the convection process, although acoustic deadening properties increase with a larger gap. Certainly with my attempts with film and with acrylic sheet, the results have been stunning. Moisture between the panes can be cut down or removed with some silica gel crystals.

 

I found that with the large metal framed windows on our boat, there was a huge heat loss through our windows in the winter months as the glass starts to drop to outside temperature and the heat from the boat is transferred through it. This was also producing a large convection movement in the boat, making the cold air fall to the floor creating draughts and cold spots. More heat just increased the effect. Our basic double glazing has completely cured this and reduced the amount of heat we need to produce, stopped condensation and reduced our costs. As for extracting moist air, rather than letting it run down the windows, a 4" computer case fan running at half speed at very low power consumption, sucks air out through a mushroom, drawing fresh air in through the vents.

 

It has all been highly successful for us and I would be interested to here if anyone else has had similar results

Roger

[John Orentas]

Yes. 20mm is the optimum gap but then more usual 8mm is very little worse for thermal insulation. I used to make GG units, nobody bothers with gas filling or even drying, the big companies pull your leg about all this, one chap tried to tell me they were all filled with nitrogen. If they are assembled in warm, dry factory conditions they work perfectly well and there is always that silica stuff in the bottom below that perforated trim. I always wonder why more people don't fit secondary glazing, that's the best way to go.

Edited February 1, 2007 by John Orentas

[Roger Gunkel]

Yes. 20mm is the optimum gap but then more usual 8mm is very little worse for thermal insulation. I used to make GG units, nobody bothers with gas filling or even drying, the big companies pull your leg about all this, one chap tried to tell me they were all filled with nitrogen. If they are assembled in warm, dry factory conditions they work perfectly well and there is always that silica stuff in the bottom below that perforated trim. I always wonder why more people don't fit secondary glazing, that's the best way to go.

Yes Jon I agree about the 8mm gap being almost as good. I seem to remember that below that, the heat/cold properties are easily transferred across the gap. Most of the modern UPVC windows use the 20mm gap for the better acoustic properties. The older aluminium ones used to be 6 to 8mm with a thermal break of a rubber or plastic material built into the frame to stop heat transfer from the inner to the outer parts. There is a lot of myth and nonsense talked about regarding the contents of the air gaps, but as Pilkingtons seem to make the vast majority of sealed units for most of the DG companies, they only have silica gel in the beadings apart from the highly specialised units.

 

As you say, secondary double glazing is an excellent way to solve the heat loss and condensation problem with the added bonus of being able to open the outer hoppers when required through the sliding inners. The only problem with supplied ones seems to be the cost, and I was quoted over £200 per window. There are a couple of companies on the internet that supply kits of various types and I did find one that supplies magnetic sealing strips for quick removal, but I can't at the moment find who they are.

Roger

[smileypete]

There are a couple of companies on the internet that supply kits of various types and I did find one that supplies magnetic sealing strips for quick removal, but I can't at the moment find who they are.

Roger

 

Probably Abel Magnets:

 

Abel Magnets

 

or try Ebay

 

cheers,

Pete.

[DHutch]

Yeah, its very supprising no one has successfull marketed a split-frame, double glazeded, boat window.

- They are a few knocking about, but nothing has really seamed to take the bull by the horns and made a reall goer of if it.

- Fair enough single is enough for most "summer boats" but for thoughs with the money, and people living onboard....?

 

 

 

Daniel

[chris w]

I understood that there is no vaccuum in a double glazed window, merely moisture removal from the trapped air. A vaccuum would certainly give wonderful insulation but I understood was totally impractical due to the difficulty of greating a vaccuum and the resulting pressure of around 14lbs per square inch needing a huge thickness of glass.Roger

 

 

Just on the pressure issue, surprisingly thin glass will withstand a very large surface pressure, such as vacuum flasks or light bulbs both of which make a satisfying bang when they implode.

[blackrose]

Yeah, its very supprising no one has successfull marketed a split-frame, double glazeded, boat window.

- They are a few knocking about, but nothing has really seamed to take the bull by the horns and made a reall goer of if it.

- Fair enough single is enough for most "summer boats" but for thoughs with the money, and people living onboard....?

Daniel

 

What about these portholes http://www.caldwellswindows.co.uk/Porthole2.htm

 

I wish I had them....

 

They don't seem to do any other double glazed windows - perhaps the larger surface area of bigger windows makes dimensional stability an issue.

Edited February 7, 2007 by blackrose

[Maffi]

I know I will get a slap for this, but what's condensation?

 

3/4of my windows are open for at least half of the day. Condensation? No Problem!

[Darcy]

Just a thought, and my knowledge of boats is limited to hiring, so I'm no expert. ......

 

Several posts have suggested using washing up liquid to prevent condensation. Washing up liquid is a surfactant, that is it reduces the interfacial tension between water and air and between the water and the surface it is sitting on. It is interfacial tension that keeps water in droplets on a window, or makes the water on a windowsill sit as a well defined oval sometimes several mm thick. If you add a surfactant to the water, the interfacial tension is reduced and the water "smeared out". You will no longer see the water droplets on the window, but the water is still there, just as a thin film. You'll no longer see the pools along the bottom of the frame, the water can now flow easily out of them and down the wall. Possibly worse, the water is more likely to soak into the surface (wood) on which it sits.

 

(If you want to try an experiment, go outside when its been raining and there are nice large drops of water on the roof of your boat, and add a drop of washing up liquid to them, then do it on a lmore porous surface).

 

So, my experience of boating is very limited, but I'd be concerned about using washing up liquid to "prevent" condensation.

 

Ann

[blackrose]

I know I will get a slap for this, but what's condensation?

 

3/4of my windows are open for at least half of the day. Condensation? No Problem!

 

What about the other half?

[tomsk]

What about the other half?

 

I think Maffi is alluding to the fact that if there is adequate ventilation you will minimise condensation (but there again I 'know nothing about boats' - Mike W/A BlackRose)

[John Orentas]

I have to agree with Maffi this condensation thing is grossly exaggerated, the only time I see any condensation is when I have just boarded the boat and not yet lit the stove, I don't live on the boat, once everything has stabilised I never see any at all. Yes I too know all about cold spots and the like but if a cabin has been adequately insulated and kept dry it will never suffer from condensation.

 

If a boat is suffering condensation it is because there is water swilling around somewhere, under the floor is the usual place, nothing to do with aluminium window frames. Get rid of the water and the condensation will disappear with it.

Edited March 6, 2007 by John Orentas

[blackrose]

I think Maffi is alluding to the fact that if there is adequate ventilation you will minimise condensation (but there again I 'know nothing about boats' - Mike W/A BlackRose)

 

Come on give it up, that was weeks ago! Odd how some people who like to dish it out often can't take a bit of stick themselves.

 

Anyway back on topic. Of course window ventilation will help with condensation but unfortunately on cold winter nights this lets all your heat out. With all the compulsory upper & lower fixed ventilation points there should be adequate ventilation on most boats without having to open windows. I don't think my boat or the topic starter's boat suffers from poor ventilation.

 

Maffi, from my side of the canal your windows look fairly unusual - are those black frames painted, powder coated, or rubberised?

 

 

...this condensation thing is grossly exaggerated, the only time I see any condensation is when I have just boarded the boat and not yet lit the stove, I don't live on the boat, once everything has stabilised I never see any at all. Yes I too know all about cold spots and the like but if a cabin has been adequately insulated and kept dry it will never suffer from condensation.

 

If a boat is suffering condensation it is because there is water swilling around somewhere, under the floor is the usual place, nothing to do with aluminium window frames. Get rid of the water and the condensation will disappear with it.

 

I don't have any water swilling around anywhere on my boat - my bilges are bone dry, but on cold nights with the stove keeping the boat warm I often wake up in the morning to find my window frames wet. It's not a major problem - I don't think anyone claimed it was or has been exaggerating. Condensation occurs when warm air meets a cold surface and it's a fact that single glazed windows & metal frames will attract condensation on a warm boat in winter precisely because they are not insulated and the thread was simply looking for solutions.

Edited March 7, 2007 by blackrose

[elessina]

We have good ventilation. In generally the condensation on the aluminium window frames only occurs at a night time, when the outside temperature falls below around 5 degrees, so it does not occur every night. It is also worse during / after cooking (even though we open windows during this time). I feel sure a cooker hood with extractor fan ducted to outside will be a big help (we have the hood, just needs to be ducted to outside - another job!). We have experimented with keeping a dehumidifier on high (expensive!) and keeping the room at around 30% relative humidity (very dry) but condensation still forms. Tom (and Sophie)'s cure with wood surround is a good one, together with the foam bungs.

 

Maffi, do you keep your windows open at night, when outside is below freezing and inside is around 21 degrees?

 

We have not yet done the wood surround or foam bungs (next year!), but have found that with an occasional wipe over, the condensation has not caused any mould or turned any of the wood black – which is what I was most fearful about…… as you say Blackrose, it is not a major problem and it's a fact that metal frames will attract condensation on a warm boat in winter, when living on board.

 

I think if you live on board a nice warm boat (21+ degrees) any exposed aluminium window frame will condensate whenever it is near or below freezing outside. The only cure is to insulate them (so they are not exposed / visible inside), this is what the wood surround and foam bugs do.

 

But it is not just on boats, wherever you 'live' aluminium window frames will condensate. I think the main reason why house windows have moved away from aluminium frames to UPVC is condensation. There is a good chance that In 10 years time we (all live-aboards) will all be ripping out our boat aluminium frames for UPVC ones (it just needs someone to manufacture a decent boat UPVC window frame!!).

 

Ian

Elessina