Thermal Performance & Energy Savings
Discover how much you can save with secondary glazing. Our interactive comparison widget shows real thermal performance data, energy savings, and payback periods for different glazing types.
Understanding Thermal Performance
Secondary glazing creates an insulating air gap between your existing window and a new inner panel. This dramatically reduces heat loss and improves comfort.
What is U-Value?
U-Value measures how much heat passes through a window. Lower values mean better insulation. Single glazing typically has a U-Value of 5.0 W/m²K, while secondary glazing can reduce this to 1.8-2.8 W/m²K.
Heat Loss Reduction
Secondary glazing can reduce heat loss through windows by 44-64% depending on the material and gap size. This translates directly to lower heating bills and improved comfort.
How Secondary Glazing Saves Energy
1. Air Gap Insulation: The gap between your original window and the secondary glazing (typically 100-150mm) acts as a thermal barrier, trapping still air which is an excellent insulator.
2. Reduced Convection: By creating a sealed cavity, secondary glazing minimizes convection currents that would otherwise transfer heat from your warm room to the cold glass.
3. Eliminating Draughts: Modern secondary glazing systems seal tightly, preventing cold air infiltration around window frames that can account for significant heat loss.
4. Low-E Coatings: Optional low-emissivity coatings reflect heat back into your room while allowing light through, further improving thermal performance.
Interactive Performance Comparison
Adjust the sliders below to match your situation and see how different secondary glazing types compare in terms of energy savings, temperature improvement, and thermal performance.
Your Scenario
Adjust the values to match your situation
Typical UK winter: 0-5°C
UK average: £1,200-£1,800
Single Glazing (Existing)
No secondary glazing - baseline
Acrylic Secondary
3-4mm acrylic panel
4mm Glass Secondary
Standard glass secondary glazing
6mm Glass Secondary
Thicker glass for better performance
Low-E Glass Secondary
Low-emissivity coating
Key Insights
Best value: 4mm glass secondary glazing offers excellent performance at a reasonable cost, with 50% heat loss reduction.
Maximum savings: Low-E glass can reduce heat loss by up to 64%, saving £960/year based on your scenario.
Quick payback: Most secondary glazing systems pay for themselves in 3-7 years through energy savings.
Real-World Factors Affecting Performance
Factors That Improve Performance
- ✓ Larger air gap (100-150mm optimal)
- ✓ Well-sealed installation
- ✓ Low-E coated glass
- ✓ Thicker glazing panels
- ✓ Quality frame materials
- ✓ Proper maintenance
Common Performance Reducers
- ✗ Poor sealing or gaps
- ✗ Very small air gaps (<50mm)
- ✗ Damaged or warped frames
- ✗ Missing weather seals
- ✗ Poorly fitted units
- ✗ Condensation between panes
Maximizing Your Energy Savings
Choose the right type: For best thermal performance, opt for 4mm or 6mm glass secondary glazing with a 100mm+ air gap. Low-E glass is worth the upgrade if you're in a very cold climate.
Professional installation matters: A well-fitted system with proper seals can perform 20-30% better than a poorly installed one, even with the same materials.
Combine with other measures: Secondary glazing works best as part of a whole-house approach including loft insulation, draught-proofing, and efficient heating controls.
Maintain your system: Check and replace seals annually, keep tracks clean, and ensure panels close properly to maintain optimal performance year after year.