Window Spacers - What's the difference?

Reducing energy use and carbon emissions is currently a top priority in the building and construction sector as well as for residential homeowners. As the push for more energy-efficient products and technologies continues, window manufacturers are looking to take advantage of spacer technologies to improve their windows' all-over energy efficiency ratings. Of course, if you talk to the manufacturers, they’ll tell you that their technology is better than all the rest.

This article summarizes spacer technologies, types, terms and efficiencies and discusses the rationale behind some of them.

What’s a spacer?

Window glass spacers or space bars are strips of plastics, metals or foams that separate, support and help seal in functional gasses that are injected between the panes of glass in a window. Spacers are bonded between glass panes with various sealing materials to help create an air-tight cavity.

Warm Edge Technology (WET)

When we talk about the main goal and the effectiveness of a window spacer, we are really talking about creating a “warm edge”. Warm Edge Technology (WET) refers to the thermal interaction between multi-panes of glass, the window frame, and the spacer at the sealed edge of an insulating glass window (IGU). The lower the energy loss between the inside and outside of the window, the warmer the spacer edge and the lower the heat loss through the sealed unit.

A perfect spacer

If there was such thing as a perfect spacer it would:

1. The seal

The primary function of a seal between multiple glass panes and a spacer is to reduce water vapour and gas permeability on the edge of the glass. However, over time most gas-filled windows will leak as much as 1% of their gas per year depending on the spacer seal, the quality of the window, the quality of the installation, air pressure, humidity, the amount of sun exposure, and the extremity of climate in which the window is exposed to.

For an IGU to have a long service life the integrity of a seal is essential:

• A primary sealant must maintain its low gas and vapour permeability
• A secondary sealant must maintain good adhesion to the glass when exposed to a variety of environmental factors.

Synthetic rubbers, typically polyisobutylene (PIB), are used as a primary seal. However, its strength decreases as temperature increases thus affecting the structural integrity of the glass unit. So secondary sealants such as polyurethane, silicon, polysulphide, hot-melt butyl or epoxy-based sealants are widely used.

2. Adaptability

Theoretically, spacers made from rigid materials like metals do not accommodate the natural expansion and contraction of the glass within the window frame as temperatures change.

3. Strength & durability

Spacers are a vital part of every window unit as they help provide structural integrity while promoting a thermal and moisture seal, increasing the windows' energy-efficiency effectiveness.

High-quality spacers are durable, strong, and have high insulating abilities. Ensuring that spacers meet these specific qualifications is determined by which type of material is used to build the spacer itself, and each material has its benefits and drawbacks. When a high-quality spacer is used along with gas fillings and e-coated windows, the energy efficiency of the window itself can be greatly improved.

4. Preventing temperature transference

Besides managing window stresses brought on by changes in temperature and air pressure, spacers that hold multiple-window panes together, also play a very important role in keeping temperatures from transferring from one window pane to another.

How to effectively minimize the transfer of temperatures from one window pane to another through the use of a variety of different window spacers is often debated between window manufacturers. Choosing the wrong spacer can reduce the energy efficiency of a double-pane window and keep you from maximizing its benefits.

5. Keeping it dry

During the window manufacturing process, it is not uncommon for small amounts of water vapour to get trapped between the panes of glass. Some manufacturers insert “desiccants” in the spacer to absorb this moisture to prevent chemical fogging and to extend the life of the window.

Spacer technology

Metal spacers:

Metal spacers are typically made from aluminium, stainless steel or other metal alloys. Because these materials are rigid, metal spacers can be more prone to sealant failure leading to gas loss, and condensation between the panes. Metal spacers are the strongest spacers and sit tight between the panes of glass, giving the window a crisp, clean look with uninterrupted sightlines.

Metal/foam spacers

Metal spacers that combine with a secure foam top provide stability, and flexibility and typically outperform metal spacers by proving a superior reduction in heat transfer and condensation.

Composite and plastic spacers

Although plastic composite materials are still rigid in nature, they do not exchange extreme temperatures the way metals do (less conductive) making their insulating properties more efficient. One interesting feature about these spacers is that some products allow the consumer to choose from a selection of colours.

Structural foam spacers

Because foam (silicone foam or ethylene-propylene-diene-monomer (EPDM)) spacers have no metal in their construction, they are arguably the most energy-efficient spacer, dramatically reducing heat/cold transfer.

Foam spacers better adapt to the expansion and contraction of the entire IGU (low thermal conductivity) as a whole, making them less prone to sealant movement (less variation in glass surface temperature) and more prone to gas retention. Although not a significant factor in the elimination of sound, foam spacers also provide a better sound barrier than metal or metal/foam spacers.

Foam spacers come in a variety of configurations (t -shaped, u-shaped) and typically fall under a brand category called Supper Spacer®.

Thermoplastic spacers

Thermoplastic spacers (TPSs) are made from polyisobutylene PIB with integrated desiccant. In contrast to other types of spacers, a TPS is extruded directly between the glass panes, creating a homogeneous and continuous edge seal.

The width of a spacer

Typically the wider the spacer, the less transference of temperatures (thermal conductivity) from one glass pane to another.

The track record

If we take out the energy-efficiency factor of a spacer and look at the overall energy-efficiency performance of an entire window, we might be able to determine which spacers actually work better than others by how long a window manufacturer is willing to warranty the insulated glass units (IGU).

It’s not just the efficiency rating that’s an important consideration when buying new windows, it’s how long the energy efficiency will be at its peak performance. If the spacer is not providing an enduring seal, then over time the energy efficiency will be lost, fogging within the IGU may occur and you’ll probably need to replace the IGU sooner than you would have anticipated.

The window warranty

Most manufacturers and installers will warranty a window over time, however, often individual parts of a window will have a different warranty. Always check the details to make sure you will get a maximized life out of the Insulated Glass Unit.

Lots to think about

Although spacers do play an important part in the energy-efficiency equation, remember it’s the window’s total performance that really counts. Having said that, there are lots of other reasons why one spacer might be better than another and this information is not always presented to customers.