Thermally broken steel
Thermally broken steel is a steel window or door frame made as an inside half and an outside half joined by insulating bars, so heat and cold cannot travel straight through the metal. Plain steel loses heat quickly; the break is what makes modern steel frames practical for homes.
Steel conducts heat very well, so a solid steel frame turns the inside of a window into a cold surface in winter. Modern residential steel systems solve this the same way aluminum does: the frame is built as two steel shells, one inside and one outside, joined by bars of a low-conductivity material. Heat trying to cross the frame has to pass through the bars.
The principle is the same as a thermal break on aluminum, which is the better-known case. The difference is the metal. Steel is strong, so sections can stay very narrow, and it is also heavier, so handling and anchoring need planning.
What to ask for
- Which system is it, and is the break built into the profile for the doors and windows you need?
- What is the whole-window or whole-door U-factor for your exact size and glass build-up, and under which test standard?
- What coating protects the steel, and how is touch-up handled?
I quote thermally broken steel from your drawings. See real steel windows and doors for the systems and real steel for how it differs from steel-look aluminum.
Common questions
- Does a thermal break make a steel window as efficient as a triple-glazed aluminum window?
- Not automatically. A thermally broken steel frame is a big improvement over plain steel, but the whole-window result depends on the system, the glass and the size. I compare the numbers for your climate zone before you order, and I say so if aluminum is the better fit.
- Is there a US rating for these steel systems?
- The thermal values published for European steel systems are European test results, not a US rating. Documentation is handled per project.