Aluminum Windows
If your house has thin metal window frames and it was built or renovated before roughly 1990, you probably have aluminum windows without a thermal break, and they are almost certainly the worst-performing part of your building envelope.
Aluminum conducts heat roughly a thousand times better than vinyl, which is why uninsulated aluminum windows frost, sweat and feel cold in upstate winters. They remain appropriate for commercial applications with a thermal break, and are generally the wrong choice for a Capital Region home.
The physics is not subtle. Aluminum conducts heat about a thousand times better than vinyl and about five times better than steel. A bare aluminum frame is effectively a heat pipe running from your warm interior to the outdoors. On a ten degree January morning, the interior surface of that frame is close to outdoor temperature, which is why it frosts over, why water runs down onto the sill, and why the room never feels warm no matter what the thermostat says.
There is no repair for this. New weatherstripping, new glass, new hardware, none of it changes the conductivity of the frame. This is the one window situation where we will tell you flatly that replacement is the only real answer.
Thermally broken versus non-thermally broken
Modern commercial aluminum is not the same product as the residential aluminum from the 1960s and 70s.
| Non-thermally broken | Thermally broken | |
|---|---|---|
| Construction | Solid aluminum frame | Two aluminum sections split by a polymer barrier |
| Cold bridge | Severe, full conduction | Substantially reduced |
| Winter frost and condensation | Routine | Much less common |
| Typical era | Pre-1990 residential | Modern commercial |
| Appropriate use here | None in a home | Commercial storefront and curtain wall |
| Sight lines | Very slim | Slim |
Where aluminum is still the right material
- Commercial storefront systems, where thermally broken aluminum is the industry standard and the strength is needed.
- Curtain wall and large glazed commercial facades.
- Very large residential openings where slim sight lines are architecturally essential and a thermally broken system is specified.
- Screen and storm door frames, where thermal performance is irrelevant.
- Exterior capping and coil stock, where aluminum is the standard material and always has been.
- Commercial entrance doors, where durability under heavy traffic outweighs thermal concerns.
What replacing aluminum actually does for a house
This is the single most dramatic before-and-after we see. In a Rotterdam ranch or a Niskayuna split with original 1960s aluminum, homeowners routinely describe one room as impossible to heat. Replace the aluminum with insulated vinyl or fiberglass and that room becomes usable. Part of it is air leakage, since old aluminum units also tend to have degraded weatherstripping. But most of it is that the cold frame surface was driving a convection current, pulling room air down across the cold glass and frame and pushing it across the floor. Eliminate the cold surface and the draft stops even though no air was actually leaking.
Ranges reflect typical Capital Region projects and are for planning only. Every Sundog quote is written, itemized, and free.
Frequently asked questions
Why do my aluminum windows frost on the inside?
Because aluminum conducts heat about a thousand times better than vinyl, so the interior surface of the frame sits close to outdoor temperature on a cold morning. When warm indoor air touches that cold metal, moisture condenses and then freezes. It is a property of the material, not a defect in your particular window.
Can aluminum windows be fixed to stop the condensation?
Not meaningfully. You can reduce indoor humidity, which lowers the dew point and helps at the margin, and you can replace failed weatherstripping to cut air leakage. But the cold frame surface remains, because it is the material. This is the one situation where replacement is genuinely the only fix.
What is a thermal break?
A polymer barrier that splits an aluminum frame into separate interior and exterior sections, interrupting the path that heat takes through the metal. Modern commercial aluminum is thermally broken and performs acceptably. Residential aluminum from before roughly 1990 generally is not, and that is the difference.
Should I replace my aluminum windows?
In a home in our climate, yes. Uninsulated aluminum is the worst common window material for a heating-dominated climate, and replacing it typically produces the most noticeable comfort improvement of any window project. Homeowners consistently tell us the room felt different the same day.
Are aluminum storefront windows a problem too?
Modern commercial aluminum is thermally broken and performs reasonably. Older commercial aluminum from the 1960s through 80s often is not, and those buildings have cold perimeter offices and condensation problems for the same reason houses do. It is a common finding when a commercial building gets an energy audit.
Is aluminum ever better than vinyl?
On strength and sight lines, yes. Aluminum is far stronger, which is why commercial storefront and curtain wall systems use it, and why it can be made with much slimmer profiles. For a heated residential building in upstate New York, that strength advantage does not outweigh the thermal penalty.
Related reading
Not sure which is right for your house?
We will walk the house, measure every opening, and tell you which option actually fits your budget and your architecture.