High Performance Windows


Reduced Energy Consumption

  • Improves passive solar gain, reduces overheating issues through selective glazing.
  • Decreases heat loss through conduction and air leakage.
  • Reduces cooling costs.

Improved Comfort Level

  • Reduces drafts and the effect of cold surfaces on comfort level.
  • Reduces sound transmission from exterior.
  • Minimizes condensation-related moisture problems.
  • Thinner window frame profiles can improve natural day-lighting.

Reduced Environmental Impact

  • Lowers emissions from household fuel-fired space heating systems.
  • Reduces consumption of non-renewable fuel resources.
  • Improves existing housing stock.

Figure 1 — High Performance Window

The light shines through three large high performance windows onto the stone tile floor in the EcoTerra EQuilibrium demonstration home.


ENERGY STAR windows can reduce your home energy costs by 7 to 12 percent, depending on the units they are replacing.

Glass is a very good conductor of heat. Every square metre of conventional window area loses up to ten times as much heat as a square metre of a well-insulated wall through cold winter nights. With selective glazing, combinations of low-E coatings and gas fills suited to the orientation, high performance windows can gain more energy during the day than they lose at night.

Window replacement is costly, but will provide cost savings in energy use, make your house more comfortable and add to the resale value.

Existing windows that have solid sashes and hardware can be fitted with inserts. The old window frames and hardware are removed, and a new window unit with a low-profile frame is inserted into the original frame. This option can be a very cost-effective solution where there is no rot or other damage to the existing frame.

In most jurisdictions in Canada, local building codes require windows in new houses and major renovations to meet a certain standard: a maximum U-value (or minimum R value) based on the winter (January) design temperature (as referenced in the code) for the location of the house. Alternatively, one can use the Natural Resources Canada (NRCan) list of window manufacturers that participate in the Canadian ENERGY STAR® initiative (http://www.nrcan.gc.ca/energy/products/energystar/participants/manufacturers/13512). ENERGY STAR® rated window products, that qualify for the climatic zone in which you live — or for colder zones — meet or exceed the building code requirements.

Figure 2 — PVC window sample

A cross section of a corner of a high performance window showing the construction of the window frame, three panes of glass and the insulating spacers between the panes.

Figure 3 — Cutaway Image of High Performance Window (ENERGY STAR)

The side and bottom of the window frame holding multiple panes of glass covered by a low-e coating and separated by insulating spacers. The area between the panes is filled with an inert gas.

Design/Installation/Operation/Maintenance Considerations

  • Purchase Energy Star-rated units that are suited to your climate zone.
  • Ensure that the installation includes sealing the area between the rough-stud opening and the window frame itself to prevent air leakage around the window.
  • There are several parts of a window, being familiar with the terms is helpful.
    • Window frame: Frame materials include wood (which can be aluminum or vinyl clad on the outside), vinyl and fibreglass. The type of frame material impacts energy efficiency and determines how much maintenance will be required over the lifetime of the unit. Fibreglass frames can offer greater energy efficiency and ease of maintenance.
    • Glazing: the actual pane(s) of glass. There can be two, three, sometimes even four layers. Some manufacturers offer a ‘suspended film’ unit, where a thin transparent plastic film is held taut between two layers of glass.
    • Spacer: Multi-pane units have a spacer holding the layers apart. The material used for the spacer impacts the overall energy performance and condensation resistance of the window. Insulating spacers are better than metal spacers for overall performance.
    • Low-e coatings: A low-e (emissivity) coating reflects or absorbs heat energy. It can be applied in different thicknesses, in different ways and on different faces of glass, depending on whether the goal is to deflect heat out (hot climates or west-facing windows with no shading) or reflect heat in (cold climates).
    • Gas-fill: the airspace between panes of glass is filled with an inert gas, such as argon, that slows down air movement (and heat loss) between the panes of glass.
    • SHGC: Solar Heat Gain Coefficient tells you how well any given window transmits solar radiation in range from 0-1. The closer to 1, the more heat gain which helps offset space heating in the winter.
  • ‘Keeping the Heat In’, a publication of the Office of Energy Efficiency and Natural Resources Canada is a useful resource (see online link below).

What Does it Save?

The cost savings associated with installing high performance windows in a house are dependent upon a number of factors including the existing window performance, the climatic region and energy prices.

Here is an example of the possible savings a family of four living in a 2-storey house built in 1973 could see by replacing double-pane windows with clear glass, a narrow air-filled space and metal spacers in wood frames with high performance windows having 3 panes of glass, two low-E coatings, argon gas fill, and insulated spacers. In this example, the windows reduce the energy consumption related to space heating by about 4% in all areas. This example doesn’t take into account any decrease in heat loss and space heating energy use associated with air sealing around the newly installed windows that would accompany a good installation. Where energy prices are low, for example, natural gas in Calgary, the annual cost savings associated with replacing windows is very low. Although windows can be an expensive energy retrofit option, the benefits associated with them are not confined to a strict cost-benefit analysis. Primarily, the level of comfort occupants perceive is based on the temperature of the inside surface of the window — the colder the glass, the more heat a person radiates towards it, making them feel chilled. The interior face of a high performance window is a warmer, so less discomfort is felt.

Window Upgrade From 2 to 3 Pane Units

  Vancouver Calgary Toronto Montreal Halifax Whitehorse
Original Megajoules/year 45,377 51,496 45,757 35,718 49,165 62,376
Upgrade Megajoules/year 43,835 49,714 43,898 34,180 47,279 59,708
Annual Cost Savings 68 76 74 198 203 337

The chart shows cost savings associated with a mid-efficiency gas furnace in Vancouver, Calgary and Toronto, an electric furnace in Montreal, a mid-efficiency oil boiler in Halifax and a mid-efficiency oil-fired furnace in Whitehorse. Cost savings will vary according to the price of the energy source for space heating as well as the efficiency of the equipment itself.

For More Information


The information contained in this publication represents current research results available to CMHC. Readers are advised to evaluate the information, materials and techniques cautiously for themselves and to consult appropriate professional resources to determine whether information, materials and techniques are suitable in their case. The text is intended as general information only and project and site-specific factors of climate, cost, aesthetics, practicality, utility and compliance with applicable building codes and standards must be taken into consideration. A number of assumptions were applied with respect to fuel prices, water rates, costs of materials, equipment and labour, planning horizons, etc. Actual reductions in energy consumption and fuel savings will vary. Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. CMHC accepts no responsibility for consequences arising from the reader’s use of the information, materials and techniques herein.

Last revised: 2013



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