Thermally broken aluminium windows - "freezing" to touch?

[MasterMark]

Hello all,

I recently had some aluminium windows and doors installed. Different models, but all Smart Systems, thermally broken.

My understanding of "thermally broken" was that unlike old-school aluminium windows, the break is inteded to isolate the inside frame from the outside. i.e., that the frame on the inside shouldn't get freezing cold in winter, or really hot in summer.

Is that accurate?

If so, does the fact that all of my frames are extremely cold to the touch (on the inside) mean that they are in some way faulty? To me logically, if the frame on the inside is a similar temperature to the outside, they can't be very energy efficient!

Any advice would be much appreciated.

 

[Gazman16]

Unfortunately aluminum is something like the 4th most conductive material so will always be cold unless heated (any metal really).
I only recommend aluminum for bi-folding doors and commercial premises personally for this reason. They will always be prone to condensation.

Think of a radiator that has been turned off all day, Even if the house is warm the metal will be cold to the touch.

 

[MasterMark]

Thanks, Gazman. Seems I got it rather wrong then!

But in that case, what is the advantage of thermally-broken windows/doors over the non-broken old style?

 

[crank39]

Its as much about not losing heat through the aluminium to the outside as well don't forget, in this day its more about mitigating heat loss rather than cold gain hence the development of warm edge spacer bars and heat reflective Low E glass

 

[MasterMark]

Thanks, Crank. But I don't quite follow - as noted, aluminium is extremely conductive, to both heat and cold. So if the cold is getting in (through the frame) surely the same principle applies both to heat getting in, and heat getting out? If the ambient temperature in a closed room is, say 22 degrees, but I then add my window, where the surface area of the frame is 5 degrees, that will contribute to a net loss of temperature inside - presumably both from cold coming in, and heat going out (through the frame, not the window given the warm edge spacer bars).

Or is my physics knowledge even worse than it was in school?!

 

[crank39]

Your frame could just be cold from the conduction of cold through the glass

1. Conduction is simply the process where heat is transferred through materials that touch one another.
2. Convection is where gasses or liquids circulate to transfer thermal energy.
3. Radiation transfers heat energy at a distance through high frequency waves such as visible light, ultraviolet light or microwaves

Do you happen to know the spec of the glass units, A rated or C rated?

 

[dishman]

What Gasman16 and Crank39 are getting at is that Aluminium is a more conductive material. So, it will transfer heat much more efficiently than other materials (upvc). Because of this it will loose heat quicker and be colder to touch.

With regards to the thermally broken thing. This does not mean they are any better at retaining heat. It just means they are not directly connected to the exterior part of the frame, so they will not get as cold i.e as cold as it is outside. But, they will still get more cold than most other materials in a house (wood, plastic walls and so on).

Because they still get cold, (but not as cold as thermally broken ones), they can still be prone to condensation. Just not as prone as older ones which got super cold to touch.

However, in your scenario, the windows may not be the only problem. Condensation forms on a cold surface if there is too much water vapour in the air and a room is poorly heated and there is not enough ventilation. So, you need to look at how ventilated your rooms are, how well heated they are and how much moisture is being produced.

I have single glazed leaded light windows, they get much much colder than any aluminium frames. They should be more prone to condensation but I do not normally get any. This is because the house is heated at a consistent temperature (not extremes of hot and cold with the heating turning off and on). Any areas that produce a lot of moisture are well ventilated (the bathroom and kitchen).

If I ever forget to ventilate, the windows at the other end of the house get condensation on them immediately. That is how quick water vapour can move through the house, cool down and condensate.

So in your case, to mitigate the condensation on the frames, you need to look at how you are heating the room they are in. What sources of moisture vapour in the house are there? Bathroom? Kitchen? Drying clothes on radiators? The last one is a big no no. How are those areas ventilated?

Looking at those things will help reduce any condensation forming on window frames.

 

[MasterMark]

Crank - the windows are A rated!

Dishman - that was also super helpful, understood on all counts. I don't have a problem at all with condensation in any of the new windows, so that's not an issue. I was surprised that the aluminium was that cold to the touch. I'd just assumed (wrongly) that the lack of direct contact with the exterior frame would have a much more noticeable impact on the interior frame temperature. Happy to be corrected and learn something new!

 

[crank39]

When you say 'windows' do you mean the frames or the glass as A rated

 

[dishman]

Actually Crank, or anyone else can you clarify this for me...

When window companies quote A rated windows. Are they combining the rating of the windows and the frame for an overall score?

When in reality the frames may be a C but the glass is A?

I had a UPVC sales guy quoting the fact they were A rated, showing me a sample frame he had in a little bag he carried. He was going on an on about it, until I asked him why there was a sticker in the inside of his example frame that said C rated.

He seemed to get a bit flustered at this point and I think indicated it was a combination of that and the glass and warm spacer bars made it an A.

But it left me a bit confused about how window companies can actually claim their windows are A rated as a whole. Or are they always just claiming that part of the windows are A rated. Or was he just talking carp....

 

[big-all]

to be fair with temperature the differential can feel great but be very small a pane off glass can be the same as the wall and the window frame but metal will take more heat input to feel warm when you touch it
cloth plastic wallpaper will quickly absorb a tiny bit off heat from your hand warming the surface enough to feel warm as heat/energy transfer is very very low/slow
metal by its nature will make you feel cold without warming up enough because the heat needs to transfer to a hundred times the area to get the same surface benefit
as an aside
if your double glazing stops condensation on the windows if the air is too moist it will simply find the next coldest surface to collect/condense on without airflow or ventilation to remove it

 

[Gazman16]

Actually Crank, or anyone else can you clarify this for me...

When window companies quote A rated windows. Are they combining the rating of the windows and the frame for an overall score?

When in reality the frames may be a C but the glass is A?

I had a UPVC sales guy quoting the fact they were A rated, showing me a sample frame he had in a little bag he carried. He was going on an on about it, until I asked him why there was a sticker in the inside of his example frame that said C rated.

He seemed to get a bit flustered at this point and I think indicated it was a combination of that and the glass and warm spacer bars made it an A.

But it left me a bit confused about how window companies can actually claim their windows are A rated as a whole. Or are they always just claiming that part of the windows are A rated. Or was he just talking carp....

Haha this is where things can get really fun and complicated lol
BFRC ratings (A,B,C etc) are basically a con, Mainly due to the fact it takes solar gain into consideration, You may have noticed we live in the UK and some windows will never get any sun.

As soon as you put a trickle vent in a window, Or leads or Georgian bars or any other change from a basic window it is no longer A,B or C rated. A trickle vent would drop it completely off the scale but they force us to fit them and still call it an A rated window.

There are very few Aluminum manufacturers that claim above a B or C rating. As far as I am concerned (and I used to make and mainly fit Ali) it is mainly a commercial product for shopfronts. For homes I only recommend them for bi-folds due to all the moving parts and the extra strength needed for the complexity.

The glass is way more thermally efficient than the frames. PVC is best due to its multiple chambers but still not as good as a modern spec sealed glass unit.

Basically U values are the best thing to go by. The ratings scale was brought out to make it less confusing to homeowners.

 

[dishman]

Interesting, I misguidedly thought that the ratings were directly related to the U-value calculations.

So, are you saying that they can off-set the frames (which will all be a"C") by using the solar gain characteristics of the glass, to give an overall rating of A?

But, all of this is meaningless anyway, because each frame or glass design has it's own U-value, which the sellers can ignore?

Wow, that is more confusing than I first thought.

 

[^woody^]

I bet the glass is freezing too, despite being thermally broken by a better insulator than is in the frames.

 

[smarkgee]

some points
1. as aluminium is highly conductive to heat, it will heat up quickly in a warm room. Of course, it won't do that if the frame is thermally broken then your heat is transferred outside
2. aluminium frames could have a faulty construction whereby the cill or other component creates the thermal bridge. eg simply assembling the item wrongly at the installer/factory
3. the window frame has no subframe and is installed onto the brick. brick gets cold and will transfer the cold to your window

I strongly suspect that incorrect installation is a big reason for condensation. With the advent of modern smart homes tools like Apple's Homehub have a humidity sensor. So we will soon be able to prove that the humidity and temperatures internally are normal and the condensation has little to do with the factors the window companies suggest. (Part L of the 2022 UK building regs requires thermal performance of windows installed after that date, sadly the FENSA certificate is used as evidence of compliance but only compliance of manufacture)