Energy-Efficient Residential Windows, Doors and Skylights
Other considerations
Installation
Have a knowledgeable professional install windows, doors and skylights according to the manufacturer's instructions. A poorly installed product may not operate properly and could cause cold drafts even though the product itself is energy efficient. Poor installation may also allow water to leak into the home, leading to costly damages.
Here are some installation criteria:
- The installation should provide an airtight, insulated seal.
- After installation, the window or door should retain its original shape and should be level and vertical. Windows may be installed at an angle (e.g. in an attic) only if they are designed to do so.
- The window or door should not support any load other than its own weight.
- Any exterior finishing, such as flashing, should prevent water penetration.
- A skylight should be well-sealed where it meets the roofing material. Any tunnel from the ceiling to the skylight should be well-insulated.
When replacing an existing window or door, there are two types of installation: retrofit and "complete tear out." A retrofit involves installing a new window or door into the frame of the window or door that is being replaced. However, a retrofit should be done only if the existing frame has not deteriorated and is properly sealed and insulated. A retrofit is usually less expensive and minimizes the disturbance to the surrounding wall and trim. It also narrows a door opening and reduces the glass area of a window by about 20 percent. Skylights are typically not retrofitted.
A complete tear out involves removing the old window, door or skylight, including the frame. A tear out allows the installer to make an airtight insulated seal between the product and the rough opening. The original door opening or window glass area is usually retained or enlarged.
For certified window installations through the Window Wise program, visit the Web site at www.windowwise.com.
Humidity issues and condensation
A certain amount of humidity in your home is desirable for comfort during the cold months. Windows, doors and skylights that are not energy efficient will often have condensation or frost on them even when the indoor humidity is at a reasonable level. This condensation, in addition to obscuring the view, can lead to mould formation on the frames and sashes. An ENERGY STAR® qualified product will allow higher indoor humidity before condensation occurs. You may even be able to turn down your thermostat and still feel comfortable. Because humidity levels are higher in bathrooms and kitchens, consider installing a product qualified for Zone D in these rooms to reduce or eliminate condensation. The table below shows when condensation is likely to form.
|
Outside temperature |
Standard window |
High-performance window |
|---|---|---|
|
0°C |
50 % |
63 % |
|
-10 °C |
38 % |
50 % |
|
-20 °C |
26 % |
40 % |
|
-30 °C |
18 % |
30 % |
|
-40 °C |
12 % |
23 % |
If the indoor humidity is too high in your home, try the following:
- Turn off the humidifier on your furnace.
- Ensure that the clothes dryer and the bathroom and kitchen fans are vented to the outside.
- Reduce the number of plants in your home.
- Store firewood outside.
If you have a mechanical ventilation system (heat recovery ventilator [HRV]), make sure that it is turned on and working properly. Some airtight houses were built without mechanical ventilation systems. If high humidity is a chronic problem in your home, consider having an HRV installed.
Excessive condensation can result in mould on window, door, wall and ceiling surfaces and, in severe cases, can damage insulation and other structural elements.
While energy-efficient windows, doors and skylights are less likely to have condensation than standard products, condensation may still occur when indoor humidity levels are too high. The first step toward reducing condensation is to always minimize moisture production in the home. If condensation problems persist, it may be necessary to increase ventilation.
NRCan's Office of Energy Efficiency (OEE) and the Canada Mortgage and Housing Corporation (CMHC) have free publications that can help you address condensation problems in your home. Contact information for the OEE and CMHC is found on the "Where Can I Obtain More Information" page.
Designing a new home
The sun's energy is free - but how you use it is critical. If you are building a new home, decisions on how many windows, doors and skylights to include in your plans, and where to install them, can have a big impact on your comfort and on your heating and cooling bills.
Homes without sufficient glass (relative to the exterior wall area) receive less heat from the sun. Too much glass can cause unnecessary heat loss in winter and excessive heat gain in summer. The tables below give the recommended area for windows, doors and skylights for bungalows and two-storey houses of varying sizes.
|
Bungalows |
||
|---|---|---|
|
Floor area |
Wall area |
Glass area |
|
1000 sq. ft. (93 m2) |
1130 sq. ft. (105 m2) |
170 sq. ft. (16 m2) |
|
2000 sq. ft. (186 m2) |
1600 sq. ft. (149 m2) |
240 sq. ft. (22 m2) |
|
3000 sq. ft. (279 m2) |
1860 sq. ft. (173 m2) |
280 sq. ft. (26 m2) |
|
Two-storey homes |
||
|
Floor area |
Wall area |
Glass area |
|
1000 sq. ft. (93 m2) |
1600 sq. ft. (149 m2) |
240 sq. ft. (22 m2) |
|
2000 sq. ft. (186 m2) |
2260 sq. ft. (210 m2) |
340 sq. ft. (32 m2) |
|
3000 sq. ft. (279 m2) |
2770 sq. ft. (257 m2) |
415 sq. ft. (39 m2) |
|
4000 sq. ft. (372 m2) |
3200 sq. ft. (297 m2) |
480 sq. ft. (45 m2) |
The placement and orientation of a window, door or skylight relative to the sun is the greatest factor affecting solar heat gain. More of a home's glazing area should be oriented to the south and west, if possible, with minimal glazing on the north and east sides of the home. However, do not concentrate too much glass in any one area. For example, a sunroom with little wall area can be nice in the winter but too hot in the summer. Heat loss through doors can be reduced by situating the door out of the path of prevailing winds or providing windbreaks, such as a porch or vestibule. Skylights should not be located where there is high humidity, such as in a bathroom near a shower or over a kitchen sink, as condensation may form in colder weather and drip on to the floor.
Glazing selection
Choosing an energy-efficient product is a good start, but you can optimize your choice by installing windows with a hard-coat, low-E coating and a high ER number on the south and west sides of the home. Through solar gain, these products will add more heat to the home than they lose. Windows with a soft-coat, low-E coating and a low U-value should be installed on the north and east sides of the home. There is less solar gain at these locations, and products with a low U-value are more resistant to heat loss.
Window coverings and film
Window coverings, such as blinds, internal shutters and insulated curtains, can also help reduce heat loss at night during cold weather and heat gain during the day in summer. They should be installed tight to the window opening; however, this will likely increase the amount of frost and condensation on the glass. (External shutters will not create this problem.) Be sure to leave the window coverings open during cool, sunny weather to allow solar gain. As with tinted glass, window films can reduce unwanted glare and solar gain during warm weather, but they do not significantly slow the rate of heat transfer. Since the installation is permanent, the lack of solar gain may lead to increase heating costs in winter that exceed the reduced cooling costs during the summer.