Passive House Institute Study 

Key Findings for Window and Insulating Glass Manufacturers

A study conducted by the Passive House Institute provides quantitative evidence of the impact of spacer bars on the energy performance of modern windows. In a conventional low‑energy house with triple glazing, the study shows that—depending on the climate zone—heating cost savings of between €23 and €25 per linear metre of glazing edge can be achieved over the service life when highly efficient non‑metallic warm‑edge spacer bars are used instead of aluminium spacers.

Lower Heating Costs for End Customers – A Market Opportunity for Manufacturers

According to the study, the reduction in heating costs is substantial enough that windows equipped with warm‑edge spacers are economically beneficial for end customers despite a slightly higher purchase price.
For example, in the low‑energy building with triple glazing analysed in the study, lifetime heating cost savings over a 40‑year usage period amount to:

€2,463 in a cool/moderate climate
€2,260 in a cold climate

In the low‑energy building with double glazing, the corresponding savings are:

€1,864 (cool/moderate climate)
€1,690 (cold climate)

For window and insulating glass manufacturers, this represents a clear economic opportunity: high‑quality warm‑edge spacer bars are only marginally more expensive per linear metre than aluminium spacers, while delivering significantly higher value to end customers.

Reduced Building Heating Demand with Warm‑Edge Spacers

Compared with aluminium spacer bars, the study identifies the following heating energy savings when efficient warm‑edge spacers are used:

in a cool/moderate climate 

• in the low-energy building with triple glazing studied: 8.6 percent
• in the low-energy building with double glazing studied: 5.6 percent
• in the Passive House building studied: 22 percent 

in a cold climate

• in the low-energy building with triple glazing studied: 7.1 percent
• in the low-energy building with double glazing studied: 4.8 percent
• in the Passive House building studied: 28 percent

These results clearly demonstrate that warm edge spacer bar systems significantly improve the energy efficiency of windows and, consequently, of entire buildings.

Why the Spacer Bar Makes the Difference

After the glazing and the frame, the spacer bar is an important component influencing the thermal performance of modern insulating windows. If the spacer bar exhibits a high heat transmission coefficient, considerable heat losses occur at the glazing edge - even when premium glass and highly insulated frames are used.

The study highlights substantial differences between spacer materials:

• High‑performance warm‑edge spacer: linear thermal conductivity of 0.14 W/(mK)
• Stainless steel spacer: 0.6 W/(mK)
• Aluminium spacer: approximately 160 W/(mK)

These values explain why aluminium spacers perform significantly worse from an energy perspective and why warm edge solutions are essential in energy‑efficient construction.

A Valuable Tool for Consultation and Sales

For the first time, the Passive House Institute study provides clear, independent, and quantifiable evidence of the benefits of warm‑edge spacer bars compared with conventional spacer systems. Window and insulating glass manufacturers can use these validated figures to support customer consultations, product differentiation, and sales discussions—demonstrating measurable long‑term value rather than marginal additional upfront cost.