Energy-Efficient Windows

It’s not just about the glass—the frame does a ton of the heavy lifting.

Energy Efficiency in GEALAN Windows vs. American Windows

Millo Windows & Doors uses window and door profiles from GEALAN. GEALAN has been a leader in window innovation for over half a century, creating windows that not only look beautiful but also work incredibly well. GEALAN combines German engineering precision with a deep understanding of the American climate, resulting in windows that are both stylish and energy-smart.
The data is very similar between the LINEAR and S8000 profiles.

Typical U.S. Vinyl Window

GEALAN-LINEAR

U-factor
(Thermal Insulation)

U-factor measures how well a window insulates against heat loss. The lower the number, the better the window insulates.

0.28 – 0.30 (double) → 0.22 – 0.25 (triple)

0.27 (double) → 0.22, as low as 0.16 (triple)

GEALAN matches or exceeds Energy Star v7.0 criteria across all U.S. zones.
Supports thicker triple glazing (≈32 mm) for superior insulation.

Solar Heat Gain Coefficient (SHGC)

Solar Heat Gain Coefficient (SHGC) indicates how much solar heat the window lets in. In warmer climates, a lower SHGC is preferred to minimize heat gain and keep your home cooler. Conversely, in colder climates, a higher SHGC can help capture solar warmth for passive heating.

0.20 – 0.49

0.19 – 0.55 (depending on glass)

No major difference because this data is not highly affected by frame.

Visible Transmittance (VT)

Visible Transmittance (VT) measures how much natural light passes through the window. The higher the VT, the more daylight comes into your home, thence reducing the need for artificial lighting and enhancing indoor comfort.

0.40 – 0.59

0.43 – 0.55

No major difference on light and transmittance.

Structural Strength (Design Pressure/Performance Grade)

Structural Strength measures how much pressure (from wind or impact) a window can withstand before bending or breaking.

PG 30-50 (≈30-50 psf)

CW-PG 105 (±105 psf)

2-3x stronger; commercial-grade performance suitable for high-rise or coastal zones.

Water Resistance

Water Resistance indicates how well a window prevents water leakage under pressure.

4.5-7.5 psf

No leakage at 15 psf (720 Pa)

2-3x higher resistance → superior protection against wind-driven rain and storms.

Airtightness

Airtightness measures how much air leaks through the window at a given pressure.

0.10 – 0.30 cfm/ft2 (limit = 0.30)

0.05 cfm/ft2 (at 1.57 psf)

Even though a window’s U-factor measures how well it resists heat transfer, it doesn’t account for air leakage. A window with good thermal insulation but poor airtightness will still let cold air in and warm air out, resulting in drafts and higher heating costs.
With an airtightness of 0.05 cfm/ft2, GEALAN-LINEAR is 2-6x tighter than typical U.S. double-hung windows, ensuring true comfort and energy efficiency in real-world conditions.

NAFS Class

Class R or LC (Residential/Light Commercial) – suitable mainly for homes or low-rise buildings.

Up to AW (Architectural Window) – top-level performance for both residential and commercial projects.

NFRC/Energy Star

Typically limited to mid-range zones; less efficient in colder climates.

Fully compliant; triple-pane meets Northern Zone Energy Star Criteria.

GEALAN-LINEAR

U-factor (Thermal Insulation):
0.27 (double) → 0.22, as low as 0.16 (triple)

Solar Heat Gain Coefficient (SHGC):
0.19 – 0.55 (depending on glass)

Visible Transmittance (VT):
0.43 – 0.55

Structural Strength (Design Pressure/Performance Grade):
CW-PG 105 (±105 psf)

Typical U.S. Vinyl Window

U-factor (Thermal Insulation):
0.28 – 0.30 (double) → 0.22 – 0.25 (triple)

Solar Heat Gain Coefficient (SHGC):
0.20 – 0.49

Visible Transmittance (VT):
0.40 – 0.59

Structural Strength (Design Pressure/Performance Grade):
PG 30-50 (≈30-50 psf)

U-factor measures how well a window insulates against heat loss. The lower the number, the better the window insulates.
Solar Heat Gain Coefficient (SHGC) indicates how much solar heat the window lets in. In warmer climates, a lower SHGC is preferred to minimize heat gain and keep your home cooler. Conversely, in colder climates, a higher SHGC can help capture solar warmth for passive heating.
Visible Transmittance (VT) measures how much natural light passes through the window. The higher the VT, the more daylight comes into your home, thence reducing the need for artificial lighting and enhancing indoor comfort.

GEALAN-LINEAR

U-factor (Thermal Insulation):
0.27 (double) → 0.22, as low as 0.16 (triple)

Solar Heat Gain Coefficient (SHGC):
0.19 – 0.55 (depending on glass)

Visible Transmittance (VT):
0.43 – 0.55

Typical U.S. Vinyl Window

U-factor (Thermal Insulation):
0.28 – 0.30 (double) → 0.22 – 0.25 (triple)

Solar Heat Gain Coefficient (SHGC):
0.20 – 0.49

Visible Transmittance (VT):
0.40 – 0.59

• GEALAN matches or exceeds Energy Star v7.0 criteria across all U.S. zones.
• Supports thicker triple glazing (≈32 mm) for superior insulation.
• No compensation on light and transmittance.

U-factor measures how well a window insulates against heat loss. The lower the number, the better the window insulates.
Solar Heat Gain Coefficient (SHGC) indicates how much solar heat the window lets in. In warmer climates, a lower SHGC is preferred to minimize heat gain and keep your home cooler. Conversely, in colder climates, a higher SHGC can help capture solar warmth for passive heating.
Visible Transmittance (VT) measures how much natural light passes through the window. The higher the VT, the more daylight comes into your home, thence reducing the need for artificial lighting and enhancing indoor comfort.

GEALAN-LINEAR

U-factor (Thermal Insulation):
0.27 (double) → 0.22, as low as 0.16 (triple)

Solar Heat Gain Coefficient (SHGC):
0.19 – 0.55 (depending on glass)

Visible Transmittance (VT):
0.43 – 0.55

Typical U.S. Vinyl Window

U-factor (Thermal Insulation):
0.28 – 0.30 (double) → 0.22 – 0.25 (triple)

Solar Heat Gain Coefficient (SHGC):
0.20 – 0.49

Visible Transmittance (VT):
0.40 – 0.59

• GEALAN matches or exceeds Energy Star v7.0 criteria across all U.S. zones.
• Supports thicker triple glazing (≈32 mm) for superior insulation.
• No compensation on light and transmittance.

U-factor measures how well a window insulates against heat loss. The lower the number, the better the window insulates.
Solar Heat Gain Coefficient (SHGC) indicates how much solar heat the window lets in. In warmer climates, a lower SHGC is preferred to minimize heat gain and keep your home cooler. Conversely, in colder climates, a higher SHGC can help capture solar warmth for passive heating.
Visible Transmittance (VT) measures how much natural light passes through the window. The higher the VT, the more daylight comes into your home, thence reducing the need for artificial lighting and enhancing indoor comfort.

GEALAN-LINEAR

U-factor (Thermal Insulation):
0.27 (double) → 0.22, as low as 0.16 (triple)

Solar Heat Gain Coefficient (SHGC):
0.19 – 0.55 (depending on glass)

Visible Transmittance (VT):
0.43 – 0.55

Typical U.S. Vinyl Window

U-factor (Thermal Insulation):
0.28 – 0.30 (double) → 0.22 – 0.25 (triple)

Solar Heat Gain Coefficient (SHGC):
0.20 – 0.49

Visible Transmittance (VT):
0.40 – 0.59

• GEALAN matches or exceeds Energy Star v7.0 criteria across all U.S. zones.
• Supports thicker triple glazing (≈32 mm) for superior insulation.
• No compensation on light and transmittance.

Lower Your Energy Bill With European Windows

Millo Windows & Doors are not just a piece of glass; they’re an entire system designed to turn your house into a comfortable, quiet, and cheap-to-run space.
Tell us about your project and get a head start on enjoying the fantastic benefits our products bring!

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Multi-point locking + continuous compression gaskets

resulting in exceptional air & water sealing.

Steel-reinforced profiles

resulting in high rigidity, larger sash sizes, and durability.

Dual-action (Tilt + Turn)

resulting in easy ventilation, cleaning, and secure operation.

European engineering

resulting in commercial-grade strength with a residential aesthetic.