Many factors affect a window’s thermal insulation. These include the number of panes, the gas filling between them, window size, pane thickness, profile thickness, the number of chambers in the profile or the quality of the timber, the type and number of seals, and the often overlooked installation method.
To calculate thermal transmittance, we use the following formula:| Uw = | Ug * Ag * Uf * Af * Ψ * L |
| Ag + Af |
- Ug - thermal transmittance of the glazing
- Ag - glazing area in m²
- Uf - thermal transmittance of the frame
- Af - frame area in m²
- Ψ - linear thermal transmittance of the thermal bridge at the junction between glazing and frame
- L - linear length of the thermal bridge at the junction between glazing and frame
As the formula above shows, a window’s thermal transmittance is affected by the following components:
- glazing (glazing unit construction and the gas filling between the panes, as well as glazing area)
- window profile (construction and material properties)
- material properties of the spacer bar
- how the glazing is secured in the frame
- window size
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