Consumer's Guide – To buying Energy-Efficient Windows and Doors

Catalogue No.: M-92-156/2001E
ISBN: 0-662-27162-9

Section 3 –
Understanding Basic Terms

3.1 Window and Door Types

There are two types of windows: those that open and those that don't–called operable and fixed, respectively (Fig. 4). Use as many fixed windows as codes allow, keeping in mind that floors with bedrooms need at least one operable window for emergency exit. Fixed windows are more efficient because of their better airtightness characteristics. They also offer the most safety and security.

Of the operable units, there are many forms: awning, casement, hopper, horizontal slider, vertical slider (either single- or double-hung) and turn-and-tilt (Fig. 5).

There are two ways of sealing operable windows to minimize air leakage: with a compression or a sliding seal. Windows with compression seals are generally the more airtight of operable types and should be the window of choice whenever possible. Casement, awning, hopper and turn-and-tilt windows, for example, should have a closure/locking mechanism that pulls the unit tight against the seal (Fig. 6). Make sure the gasket is a compression, neoprene rubber type.

Doors are a little less complicated. They are either: solid, solid with an insulated core, solid with window(s), or solid with an insulated core and window(s). Patio doors operate like a large horizontal sliding window. Hinged French doors, with a solid centre post to close against, or rolling doors with a compression-fit like an aircraft door, are more energy-efficient (Fig. 7).

Some materials reduce heat flow better than others. Solid wood doors, for example, are not as good as metal-clad, insulated core doors, depending on the style of door and insulation material used to fill it (Fig. 8).

Otherwise, doors have a frame, sill, optional glazing, and rough frame opening in a wall as do windows (Fig. 9). Like windows, some doors are even installed in the frame and sill system while still at the factory.

3.2 Glazing Parts

Glazing is the generic term for the transparent–or sometimes translucent–material in a window or door. A window may be divided into one or more sashes, some of which may move and others which may be fixed. For example, a double-hung window generally has two moveable sashes, while a single-hung window has just one moveable sash (Fig. 10).

A sash may be divided into two or more lights (panes of glass) held in place by mullions and muntins (Fig. 10).

3.3 Glazing Types

When we speak of windows, we tend to use the terms single-, double- or triple-glazed. These terms simply refer to the number of panes of glass incorporated into the window unit: single-glazed–one pane; double-glazed–two panes; triple-glazed–three panes (Fig. 11).

All windows in Canada should be at least double-glazed. To determine the number of glazings in a particular window, hold a light next to the glass and count the reflections (Fig. 12). In a double-glazed window, for example, you'll see two main reflections, corresponding to the number of glazings. (If you look carefully at each reflection, there are actually two reflections very close together, bouncing off both surfaces of each pane.)

Most window manufacturers offer several types of glazing which affect the insulation value of the window and the likelihood of condensation forming on the glass. Sometimes, transparent plastic films are placed inside the glazing unit between the panes of glass to increase energy efficiency.

A variety of coatings on the glazing surfaces –plastic films, or inert gases between glazings, for example–can increase the insulating value of a double-glazed window to more than equal that of a standard triple-glazed window. Coatings are often used with gas fill.

Most windows now incorporate sealed, insulated glazing (IG) units in which two or more glazing layers are sealed around the outside edge to prevent air or moisture from entering the air space, eliminating dirt and condensation between glazings. If moist air finds its way into the sealed air space, condensation may form between the glazings. This is usually caused by a faulty seal and cannot be corrected except by replacing the IG unit.

3.4 Spacers

If you look between the window panes in a conventional double-glazed window where the glass meets the frame, you will probably see a strip of material, known as a spacer. The purpose of spacers is to maintain a uniform separation between the panes of glass (Fig. 13).

Spacers have traditionally been made of hollow aluminum, containing a drying agent or desiccant designed to absorb the initial moisture present at the time of manufacture in the space between the glazings. Metal spacers conduct energy easily and are a significant source of heat loss and poor window performance. The best are insulating spacers often made from non-metallic materials. There are also hybrid spacers made out of metal and non-metallic materials. These materials do not conduct nearly as much heat (see Low-Conductivity Spacers).

3.5 Frames and Sashes

A window consists of a glazed unit, a frame and a sash. The glazed unit fits into the sash, and the frame holds the sash. The frame and sash may occupy as much as one third of the total window area. Both the frame and the sash can be major sources of heat loss. This heat loss is a result of conduction through the material. Heat loss can also result from air leakage, sometimes increased by expansion and contraction or warpage of a window's frame or sashes. Highly conductive materials used in the construction of the frame and sash must have thermal breaks incorporated in order to reduce heat loss. A large amount of heat loss through the sash and frame will result in the formation of condensation and frost on interior window surfaces.

Frames and sashes are manufactured from a variety of materials–aluminum, fibreglass, vinyl, wood, and combinations of these materials. Each material has benefits and drawbacks in terms of insulating value, strength, durability, cost, aesthetics and maintenance requirements. Good quality windows can be made using any of these materials. Use the Energy Rating (ER) to compare energy performance.

The ER for windows takes into account the thermal performance of the frame, sash and the glass. Refer to the ER system and the CSA-A440 window standard.

General Considerations
Check the following points on a full-sized window; some features may be visible only on a cutaway sample. Look carefully at the product literature and ask a sales representative to explain the features to you.

• Check for strong, tight-fitting sealed joints to prevent air and water leakage.

• For windows that require thermal breaks, inspect a corner cutaway sample of the frame and the sash. Ensure that the exterior and interior surfaces are separated by an insulating material (thermal break).

• For larger and heavier windows, inquire if additional reinforcement is required and how this might affect the thermal performance.

• The insulated glazing unit is held in the sash using various sealing methods to prevent water from entering the interface between the glass unit and the sash. Check the sealing system on both the interior and the exterior surfaces for an effective continuous seal. Trapped water in the sash is probably the greatest cause of failure of the glazing unit. Some manufacturers incorporate a drainage system into the sash; this feature allows any water that may otherwise be trapped to drain away.

• A price and quality comparison is essential. Low-priced, poor quality windows are not a good, long-term investment. Energy-efficient, durable and low-maintenance windows will provide energy savings, increase comfort levels, reduce or eliminate condensation on the interior surface of windows and last longer.

Aluminum
Aluminum frames are strong and durable. Aluminum maintains its strength, offers low maintenance and resists warping. Aluminum frames and sashes must be designed with thermal breaks to reduce conduction heat loss. Use the ER number to assess the effectiveness of the thermal break.

Fibreglass
In terms of energy performance, fibreglass frames rate highly. In some designs the hollow sections of the frame and sash are filled with foam insulation to further decrease heat loss. Fibreglass frames offer good structural strength, durability, and require minimal maintenance.

Vinyl
Extruded vinyl frames provide good thermal performance, and are easy to maintain. Large vinyl windows may be reinforced to increase their strength; some reinforcing materials may increase conductive heat loss. Use the ER number to assess the effect of the reinforcing material on thermal performance. Thermally welded corners can prevent air and water leakage if the welds are continuous. Hollow sections of vinyl frames can be filled with foam insulation to improve thermal performance.

Wood
Solid wood frames have a good insulating value and structural strength but require protection from the weather. Low-maintenance, factory-applied claddings and finishes are available. They must prevent water from becoming trapped behind them. Look for well-sealed corners as well as gaskets between the cladding and the glazing. Heat-conductive cladding materials should not touch the glazing or extend in from the outside of the window towards the interior. When installed in this manner, they can cause condensation problems and lower the thermal performance of the window.

Combination & Composite
The combination window frame or sash combines two or more materials, such as aluminum, fibreglass, wood, and vinyl. The objective is to obtain the best features of each material so that the frame and sash will provide good thermal performance, durability and strength, and require minimal maintenance. Combination windows use different materials separately in appropriate areas while windows made out of composite materials have frames and sashes made out of materials such as fibreglass and wood that have been "blended" together through a manufacturing process. Composite materials essentially adopt the positive attributes of the materials from which they are made, in a single unified form. No matter what frame and sash materials you consider, remember that the ER number is your best indicator of window energy performance.

3.6 Hardware

Window hardware includes the hinges, casement cranks, handles, latch plates, etc., of operable units (Fig. 19). The quality of hardware and hardware placement can affect the performance of the weatherstripping.

Weather changes can affect the durability of the hardware design, its attachment, and window members to which it is attached. During a cold winter, opening a window may cause problems if ice builds up, making it difficult to close the window tightly.

3.7 Weatherstripping

Windows should use durable, flexible gaskets to make an airtight seal between the operating sash and the window sill and frame. An airtight seal is also needed between a door and its frame. The airtightness of the joint between operable sashes and a window frame or between a door and frame depends on the type of weatherstripping used and the amount of pressure that can be applied on the joint.

Compression seals (Fig. 20 a), which can be squeezed tightly between the moving sash and the window sill and frame, and which are resilient over many years and not subject to cracking or other deterioration, are better than sliding seals with brush-type weatherstripping (Fig. 20 b).

You may not be able to avoid brush-type seals, especially if you are selecting horizontal sliders. On this type of window, look for thick brush seals with a thin flexible plastic flange embedded in the brush to minimize air leakage.

Previous Section  |   Next Section