Energy Efficiency Basics

Everything You Need To Know When It Comes To Windows And Doors

Energy Efficient Windows and Doors Made Simple

03 July 2017

Windows and Energy Efficiency

The benefits of replacing windows with energy efficient units go much further than reducing utility bills.

Energy-efficient windows can help reduce heating bills and enhance the comfort of your home. Above all that, you’re also minimising environmental impact. Marvin’s window and door range can help you achieve long-term performance and energy costs savings, in any climate.

Certification programmes provide ratings designed to indicate the efficiency of windows and doors. The performance ratings, such as U-factor and Solar Heat Gain coefficient, measure the product’s effectiveness in insulating and blocking heat from the sun. See the Glossary of terms below:

  • U-FACTOR: It measures how effectively a window holds heat inside your home. It’s a calculation of total heat flow through a window or door from inside to outside. Lower numbers define greater insulation capabilities. It’s a particularly important measure for climates with colder seasons.
  • SOLAR HEAT GAIN: When U-factor determines how much heat leaves your home, the Solar Heat Gain Coefficient (SHGC) indicates how much radiant heat enters the home. Remember, the lower the number, the less heat comes in through the window.
  • VISIBLE TRANSMITTANCE (VT): It’s the amount of visible light a window transfers. Low E coatings can obstruct solar heat gain without reducing visible light to pass through the window. A high VT is preferable to maximise daylight.

Energy Efficient Glass

What’s a good U-factor number? What’s a good SHGC?

Each homeowner seeks out different levels of efficiency, but a “good” U-factor is considered <.30. A “good” Solar Heat Gain rating, on a scale from 0 to 1, is relative to climates in different regions. Low SHGC ratings are best for southern climates with intense sun exposure, whereas higher SHGC numbers make the most sense for regions with cold winters.

What about Low E coatings?

Emissivity is the ability of a material to radiate energy (heat). Highly thin coatings of special low emissivity (Low E) metallic material are applied to glass panes of windows and doors to enhance their energy efficiency. Low E coatings, generally used on the inside layers of insulating glass, regulate the amount of light and heat either conducted through the window or reflected away.

Are triple glazed windows best?

Not always. Triple glazed windows work well when the key objective is to boost energy performance. There are options of low-E configurations for greater SHGC control, including panes filled with argon or krypton-argon gas for greater efficiency. But no matter how many panels there are, if the window is poorly produced or poorly installed, or if it allows air leakage, it will not be efficient.

Consult our team of experts to choose the best energy efficient window for your home.

Frequently Asked Questions About Energy Efficiency

Quick facts about energy efficient windows and doors for your home.


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