Common Myths About Thermally Broken Windows (And What the Facts Actually Say)

There is a lot of confusing information out there about thermally broken windows. Some of it comes from people who installed standard aluminium frames years ago and had a bad experience. Some of it comes down to the fact that window shopping does not usually come with a technical manual. Either way, the same myths keep coming up, and they push people toward decisions that do not actually serve them.

This post goes through the most common ones and explains what is actually going on.

First, What Does “Thermally Broken” Actually Mean?

Before getting into the myths, it is worth understanding what the term means.

A thermally broken window has a non-conductive barrier built into the aluminium frame. This barrier, usually a polyamide strip, sits between the interior and exterior halves of the frame. It physically blocks the path that heat would otherwise travel through the metal. Without it, aluminium conducts heat very quickly, far faster than timber or uPVC. That strip is what makes the difference between a frame that leaks heat and one that does not.

The polyamide material used in quality systems is a very poor conductor of heat compared to aluminium. That is the whole point. It turns a metal frame into something that actually holds temperature rather than just holding glass in place.

Myth 1: Aluminium Windows Are Always Cold

This is probably the most repeated myth, and there was a time when it made sense. Older standard aluminium frames with no thermal break do pull cold into the room. If you grew up in a house with single-glazed aluminium windows, you probably remember the chill near the frames in winter. That experience stuck with a lot of people.

The problem is that it describes a product most quality manufacturers stopped making decades ago. A modern thermally broken aluminium frame keeps the interior face of the frame close to room temperature. That means no cold radiating off the frame and no moisture forming on it. The frame does not feel cold because it actually is not.

The difference between a standard frame and a thermally broken one is significant. A non-broken frame loses heat roughly two to four times faster than a properly broken one. That gap is what separates a window that works against your heating system from one that works with it.

Myth 2: Thermally Broken Windows Always Cause Condensation

This is linked to the first myth but involves a different process, so it is worth separating out.

Condensation forms when a surface gets cold enough that moisture in the air settles on it. Think of a cold drink on a humid day. On an older non-broken aluminium frame, that happened easily because the frame was basically the same temperature as the outside air. On a thermally broken frame, the interior surface stays warmer, so moisture in the room air does not settle on it the same way.

If you are seeing condensation on the inside surface of the glass rather than the frame, that is usually a ventilation or humidity problem in the room itself. It is not the window’s fault. If condensation is forming between the panes of glass, that points to a failed seal inside the glass unit, which is a manufacturing or installation issue. That can happen on poor-quality products. It is not something that comes with the technology.

Myth 3: Thermally Broken Windows Only Work in Cold Climates

A fair number of Australian homeowners skip these windows because they assume the benefit is mainly about keeping heat in during winter. Sydney is not Canberra. It does not get that cold. So why bother?

That thinking only looks at half the picture. Thermal performance works in both directions. The same frame that slows heat from escaping in winter also slows heat from entering in summer. Standard aluminium frames sitting in direct sun can get very hot, and that heat moves through the frame and into the room. Thermally broken systems slow that process down. Paired with appropriate double glazed windows and the right glass, they help keep rooms cooler without the air conditioning working as hard.

For Sydney specifically, the summer benefit is often just as useful as the winter one. The thermal break matters all year, not just when temperatures drop.

Myth 4: The Glass Does All the Work

Some people assume that if they have double glazing, the frame type does not really matter. The glass is the insulating part, so the frame is just there to hold it.

That is not how it works. The thermal performance of a window is measured across the whole unit: glass, seals, spacer bar, and frame together. Good glass sitting in a standard non-broken aluminium frame still loses a lot of heat through the metal. The glass does its job. The frame undoes some of it.

A useful way to think about it: imagine insulating a wall but leaving a strip of bare metal running through the middle. The insulation works where it is, but the metal strip creates a shortcut for heat. That is what an unbroken aluminium frame does to an otherwise well-specified window. For homes trying to meet current energy standards, including the 7-star NatHERS rating now required under the National Construction Code, the frame matters as much as the glass.

Myth 5: All Thermally Broken Windows Perform the Same

Not all thermal breaks are equal. This is probably the most practical thing to understand when comparing quotes.

The width of the polyamide strip makes a real difference. Cheaper systems use a narrow strip of around 14 to 15 mm. Mid-range profiles sit around 24 mm. Better systems run 34 mm or wider, and some include foam inserts in the frame chambers as well. Each step up reduces how much heat gets through the frame.

The number of sealed air chambers inside the frame profile also matters. More chambers mean more pockets of still air, which slows heat transfer further. A frame with five chambers performs better than one with three, all else being equal.