Understanding Window Coatings (Low-E)
When shopping for energy-efficient windows, one of the most important terms you'll encounter is Low-E (Low-Emissivity) coating. These microscopically thin, virtually invisible metallic layers are deposited directly onto the surface of one or more panes of glass to improve thermal performance.
How Low-E Coatings Work
Heat naturally flows from warmer areas to cooler ones. In the winter, heat inside your home tries to escape outdoors. In the summer, the sun's heat tries to radiate indoors.
Low-E coatings work by acting like a highly selective mirror:
- In Winter: They reflect long-wave infrared heat (from your furnace and body) back into the home, preventing heat loss.
- In Summer: They reflect short-wave solar heat back outdoors, keeping your home cooler and reducing air conditioning loads.
They also block a significant amount of ultraviolet (UV) light, which protects your furniture, flooring, and artwork from fading.
Types of Low-E Coatings
There are two primary manufacturing processes for applying Low-E coatings:
1. Passive Low-E (Hard Coat)
- The Process: Manufactured using the pyrolytic process where a coating is applied to the glass ribbon while it is still semi-molten.
- The Benefit: Extremely durable.
- Best Use: Often preferred in very cold climates because they allow more of the sun's short-wave heat energy to pass through, providing passive solar heating during the winter.
2. Solar Control Low-E (Soft Coat)
- The Process: Applied using a process called Magnetron Sputtering Vapor Deposition (MSVD) after the glass is already manufactured. It is delicate and must be sealed inside the insulated glass unit (IGU).
- The Benefit: Offers lower emissivity (better insulation) and better solar heat control compared to hard coats.
- Best Use: Ideal for mixed or warmer climates where keeping summer heat out is just as important as keeping winter heat in.
Where is the Coating Applied?
An insulated glass unit (IGU) typically consists of two or three panes of glass, which creates multiple "surfaces".
- In a double-pane window, the surfaces are numbered 1 through 4 (outside to inside).
- Placing the coating on Surface 2 is common to maximize solar heat rejection (summer cooling).
- Placing the coating on Surface 3 is common to maximize heat retention (winter warming).
Modern high-performance windows often use multiple Low-E coatings across different surfaces in triple-pane setups to achieve the best possible Energy Rating (ER) and U-Factor.
Popular Brand Name Low-E Coatings
While window companies manufacture the window frames and assemble the units, the raw glass itself is usually supplied by large glass manufacturers. Here are some of the most common proprietary Low-E coatings you will see quoted by contractors:
Cardinal Glass Industries
Cardinal is one of the most widely used glass suppliers in North America. Their Low-E coatings are named by the number of silver layers they contain:
- LoE-180™: A single-layer soft coat designed for passive solar gain. Excellent for cold Canadian winters where capturing the sun's heat is desirable.
- LoE²-272®: A double-layer coating that provides a balanced middle-ground for year-round performance.
- LoE³-366®: A triple-layer coating that blocks 95% of UV rays and offers maximum solar control. Ideal for keeping homes cool in intense summer heat.
- LoE-i89®: An advanced coating applied to the inside surface (Surface 4) of the glass to reflect escaping heat back into the room without needing to move to a triple-pane unit.
Guardian Glass
Guardian produces the ClimaGuard series:
- ClimaGuard® 70/36: A high-performance residential Low-E glass balancing light transmission and solar heat control.
- ClimaGuard® 80/70: Designed specifically for cold climates to maximize passive solar heat gain.
Vitro Architectural Glass (formerly PPG)
Vitro produces the famous Solarban line, commonly seen in both high-end residential and commercial windows:
- Solarban® 60: A versatile double-silver Low-E coating.
- Solarban® 70: A triple-silver coating offering excellent solar control and high visible light transmittance.
Pilkington
Known for their pioneering glass technologies, Pilkington offers:
- Energy Advantage™: A highly durable pyrolytic (hard coat) Low-E glass that is exceptionally good at passive solar heat gain.
- Solar E™: A solar control Low-E glass that balances thermal insulation with shading.