Thermal breaks in aluminum windows

Aluminum is a superb conductor, which is exactly what you do not want in a wall. The thermal break is the part that fixes it, and "thermally broken" on a datasheet is a claim worth interrogating.

The problem, stated plainly

Aluminum conducts heat roughly a thousand times better than the insulating glass sitting inside it. An untreated aluminum frame is therefore a bridge straight through the wall: heat leaves in winter, arrives in summer, and the inner face gets cold enough to condense water out of the room air.

That last part is what people notice. Condensation on the inside of a frame is rarely a glass problem; it is usually the frame conducting.

What the break is

The frame is made in two separate aluminum sections, inner and outer, joined by a strut of polyamide — a rigid engineering plastic that carries structural load but conducts heat poorly. Our partner uses nylon PA66. The inner face is now thermally separated from the outer face.

The consequence for the building is a lower U-factor, a warmer inner frame surface, and a much higher condensation resistance number.

How to interrogate the claim

Ask what the strut is made of and how deep it is; "thermally broken" covers everything from a serious polyamide strut to a token strip. Ask for the whole-window U-factor rather than a centre-of-glass figure, because centre-of-glass conveniently omits the frame you are asking about. Then ask for the NFRC CPD number, which settles it — a whole-product rating in a public directory cannot be argued with.

A supplier who can answer the first two and not the third is telling you something.

FAQ

Are thermally broken aluminum windows as efficient as vinyl?

Not on frame conduction alone — vinyl is a poorer conductor, so a vinyl frame starts ahead. Aluminum wins on strength, which is why it can carry far larger glass areas and much slimmer sightlines, and a thermally broken aluminum window with good glazing closes most of the gap on whole-window U-factor. If your priority is the lowest possible U-factor on a small opening and looks do not matter, vinyl is the honest answer.

What is polyamide PA66 and why is it used?

A glass-reinforced engineering nylon. It is used because it does two contradictory things at once: it is stiff and strong enough to be a structural part of the frame, and it conducts heat poorly enough to interrupt the thermal bridge.

Source: Thermal break construction and PA66 material: manufacturer’s published configuration details.

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