Energy-Efficient Window Frames

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The glazing isn't the only part of a window that transfers heat: the sash and frame make up about 25% of an average window's surface area, so choosing energy-efficient materials and designs is important.

Material choices

Traditionally, wooden sashes and frames are the most common, and this still holds true today. In fact, wooden windows are the number-one selling item in construction in the US.

An alternative to wooden sashes and frames is metal, made with recycled aluminum and steel. You should never (ever!) use metal sashes and frames unless you install warm edges (see below). Metal conducts a horrific amount of heat out of your house, so the small ecological good you do in using some recycled material is completely drowned by the heating cost.

And so we're back to wood. It's a great choice: it's a renewable resource, it has a warm feel, it's flexible from an aesthetic standpoint and it's a poor heat conductor. If you choose frames made from recycled lumber, you can do even more good.

However, wood does have a down-side. Most obviously, it's not as durable as other materials, so it requires maintenance and eventual replacement. Rain and sun both affect it very badly, especially on south-facing walls. Coatings applied at manufacture can help, particularly ABS (acrylonitrile butadiene styrene) plastic cladding, but paint and most resistant coatings will eventually flake off or become useless. ABS plastic is used to create window frames that are very weather-resistant. They are available in a variety of colors (impregnated into the plastic).

Vinyl frames

The other option is vinyl, which has been around since the 1970s and is popular in Europe and Canada. Vinyl frames are made of polyvinyl chloride (PVC), which itself comes from vinyl chloride. Vinyl chloride is a known carcinogen. Although this was a significant concern in the past, manufacturers have made enormous leaps in protecting their staff from exposure, and there is no proof (or even any fear) that PVC frames can harm a home's inhabitants. Some frames are made from recycled materials.

Hollow extruded vinyl frames and sashes are comparable to wood in terms of efficiency, so they're a good choice in passive solar homes. They are extremely durable and last a long time, especially if they are UV-resistant. Vinyl frames are impregnated with color at manufacture and cannot be painted, but need little maintenance.

Vinyl frames do have a down-side, of course. The main problem is that they expand and contract significantly with temperature changes. This can loosen seals, cause cracks on edges and joins and eventually reduce the window's energy efficiency. With that said, it is true that manufacturers are aware of the problems and design frames specifically to resist these problems. Heat-welded corners hold up the best over time, so choose those if you can.

Vinyl also pales after long exposure to sunlight and becomes brittle over time. This can affect the aesthetic of your home if your windows were a bright color and end up looking sun-faded. You can't paint them back to their original color, though there are products