The battle of the panes - double vs triple glazing

triple-glaze vs double-glaze
If you are going through the process of having your windows replaced, you'll hear conflicting arguments for or against triple-glazed verses double-glazed windows.

If you are serious about getting the best quality, best energy-savings and best value in today’s window replacement market, then you really need to do your own homework, and draw your own conclusions.

This blog entry is intended to give you an impartial look at the variables and factors affecting the most current window prices and performance. We hope this information provided will help you decide which option are best for your family and your home.

Glass Efficiency

Before you start, here are a number of glass attributes that affect a window’s efficiency.

  1. Number of (glazes) panes of glass
  2. Thickness of the glass
  3. Coatings on the glass
  4. Space between the glass
  5. Material that separates the glass
  6. Gas between the glass
  7. Frame holding the glass in place

Lots to consider. Unfortunately, these attributes are rarely published and available to the average consumer. That’s why Energy Ratings are so important, they are the only standardized unbiased measurements (tested and measured by a neutral authority) available to help you make an honest comparison between windows.

Measuring Energy-Efficiency

The best resource for honest energy-efficiency measurements are available from the NRC Canadian Government sponsored Energy Star website, here you can search for windows by a variety of queries.

Below are the main energy-efficiency ratings as they pertain to glass. Keep in mind that window manufacturers typically provide customers with several glass options to help produce the desired result (e.g. less light, less heat, more insulation…) which can lower or raise energy-rating values.

Energy Star Specs - double/triple glazing

  1. U-factor (UF) - heat loss through frames, spacer and glass
  2. Solar heat gain coefficient (SHGC) - heat transmitted and absorbed that is subsequently released inward
  3. Visable transmittance (VT) -  is the amount of light in the visible portion of the spectrum that passes through a glazing material

Energy-efficiency is great, but what about about home comfort?

In Ottawa (climate zone 3) the energy-efficiency prime directive is focused on keeping heating costs down in the winter as statistics show heating costs far outweigh cooling costs. However, in many cases, energy-efficiency may mean a sacrifice in home comfort.

Unfortunately, some of the things that make a window more efficient can also result in less desirable effects:

  • Excessive heat in a room in the summer
  • Excessive brightness in a south facing window all year round
  • Furniture damage due to UV rays

This is exactly why most window manufactures give you varying levels of glass options and why when you are buying windows, even though there are manufacturing standards, you cannot really make apples-to-apples comparisons.

Comparing double-glazed windows to triple-glazed windows

OK, so which is better, triple or double glazing? For purposes of understanding the statements below, we’ll pretend we are using the same glass, gas and spacer attributes for both the triple and double-glazed windows. Here are the facts.

Home comfort

  • Triple-glazed windows are typically better than double-glazed windows at helping to keep the air temperature inside the home at consistent temperatures.
  • Triple-glazed windows typically allow for higher levels of humidity and lower condensation than double-glazed windows.

Performance and weight

Double-glazed windows

  • Weigh less than triple-glazed windows.
  • Do not have to be as strong as triple-glazed windows to support the glass.
  • Are easier to lift for installation.

Triple-glazed windows

  • Weigh more than double-glazed windows.
  • Quality triple-glazed windows are engineered to handle additional glass weight and are unaffected by the weight when operation.
  • If concerned about weight and durability, look for products with higher year warranty coverage.

Free heat and light

  • Double-glazed windows allow a little more light and solar heat into the home than triple-glazed windows.
  • Standard triple-glazed windows are slightly better at filtering out UV rays than double-glazed windows.

Thermal insullation

Triple-glazed windows typically have a better thermal Insulation (U-value) double-glazed windows.

Low-emissivity

When low-emmisive glass is being used, the extra low-emissive coating in triple-glazed glass tends to perform better at stopping the summer heat from entering the home in the summer and from escaping in the winter.

Cost

Double-glazed windows tend to be less expensive than triple glazed, although the gap between costs has been decreasing as companies that have converted to triple-glazed technology become more competitive.

Condensation

Triple-glazed windows have warmer inside-the-home glass surface temperature in the winter which can improve relative humidity levels in the home and decrease the potential for condensation.

Sound

Triple-glazed windows tend to be slightly quieter than double-glazed windows, however if sound proofing is a requirement you should look beyond standard glass configuration. For more information consult your window consultant.