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Replace old energy wasting
sliding glass doors

Q: Dear Jim: I should replace my old sliding glass patio door this winter. I can feel a draft and hear road noise through it. It also sweats, doesn't slide smoothly and probably is not secure. What features should I consider in a new one?

-Ted K.

A: Dear Ted: An old sliding glass patio door, even if it has standard double-pane glass, can be one of the biggest energy wasters in a home. Just sit by the door on a cold winter evening and you will probably feel how inefficient it is. Air leakage around the door is often the worse culprit. This is also true during the summer when warm moist air leaks indoors.

A sliding glass door is basically a huge hole in your insulated walls. Your old door may have an insulation level of R-2 at the best. When you sit near the sliding glass door at night, heat from your body radiates to the cold outdoors causing you to feel colder than the room temperature. This often makes you turn the thermostat up a little, wasting more energy.

You will be surprised at all the new efficiency features and many styles of sliding glass doors available. The highest energy efficient glass for the sliding doors is as high as R-10. This super-efficient glass has triple panes, low-emissivity (low-e) coatings on two of the glass surfaces with krypton gas in the gaps between the panes. The krypton gas is very dense, which also reduces the outdoor noise transmission through the large glass panes.

The airtight seals are also better on the new door designs. Keep in mind, a sliding glass door has a lot of mating joints that must be sealed with weather-stripping. Much of the joint's area is a sliding seal, not compression as on a casement window or a hinged door. As your new door ages, keep an eye on the condition of the weather-stripping and replace it when it is worn. The manufacturers offer replacement kits.

Much recent design attention has been given to the styling of sliding glass doors. French (Freedom) style patio doors are increasingly popular in new homes and for replacements. These have wider rails and stiles on the doorframe to simulate the appearance of double-hinged doors. Optional matching grilles can be added over the glass for additional style.

Sliding glass doors cover a large span, so the strength of the frame is critical. Typical frame material options for replacement sliding glass


doors are aluminum, fiberglass, vinyl, wood and vinyl or aluminum-clad wood.

Fiberglass is one of the best low-maintenance materials for sliding glass door frames. I use this type in my home. The frames are made with a pultruded process, which is different from how fiberglass boat hulls and car bodies are produced. Pultrusion combines long glass fibers with strong resins to create an almost indestructible frame.

A fiberglass frame expands and contracts with temperature changes (hot summer sun to cold winter nights) at a similar rate as the glass panes. This reduces stresses within the doorframe and along the seals where the glass panes rest in the frame. For a natural wood appearance, select one with a real oak veneer bonded over the indoor surface of the fiberglass frame.

Vinyl is another low-maintenance frame material to consider. Its color goes completely through the frame, so it looks good even with small scratches. Look for fusion-welded corners, metal reinforcement inside the frame and ball-bearing steel or nylon rollers. Vinyl or aluminum cladding over a wood frame minimizes its outdoor maintenance. All-aluminum frames should have a plastic thermal break between the outdoor and indoor surfaces.

The type of glass is key to energy efficiency. The triple-pane R-10 glass may be outside the budget for many homeowners. As a minimum, select double-pane, low-e glass. For hot climates, you may prefer to have tinted panes. In very cold climates, the R-10 glass may make economic sense, or choose less-expensive R-6 triple-pane glass.

There are several options that can make your sliding glass door more secure. Multipoint lock and foot lock features require a thief to take more time to pry the door open. This is particularly true with a strong frame material such as fiberglass or aluminum-clad wood. If you are really concerned about security, select double swinging or tilt/turn (swings on hinges or tilts in at top for ventilation) doors instead. Some closely resemble sliders and they are more difficult to force open.

Write for (instantly download - Update Bulletin No. 939 - buyer's guide of 15 fiberglass, vinyl and wood sliding/ hinged patio door manufacturers listing sizes, glass options, colors, decorative, and security features. Please include $3.00 and a business-size SASE. James Dulley, Illinois Country Living, 6906 Royalgreen Dr., Cincinnati, OH 45244.

James Dulley is a mechanical engineer who writes on a wide variety of energy and utility topics. His column appears in a large number of daily newspapers.

February 2004 | | 19

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