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Doors and Window

More energy can be lost through a few doors and windows than through walls and roof combined. Small wonder; rated at only T-0.9, a glass pane conducts and radiates energy both ways, which is great during sunny winter days but inefficient at night (and the reverse in summer). During the `70s, when petroleum threatened to rise to $50/bbl (it now sells for about $18), a number of door/window-insulating ideas were developed—not all of them practical. I remember one dual-pane window that could be blown full of insulating styrofoam beads. Problem was, getting them all out was nearly impossible, and little white bits flecked the inner panes.

In modern energy-saving, dual-pane sashes; interpane spaces are filled with argon or another inert gas, which, with its heavy molecules, is less conductive than still air. A low-E coating—a super-fine spray of reflective metal—is applied to inner surfaces of panes. Much as the metal grid in your microwave oven door lets light out but keeps microwaves in, the low-E coating lets visible light through but reflects infrared. Reflecting heat inward in the north, and outward in the south, the low-E, gas-filled sash has an R-4 rating.

The newest development is a window with low-E coatings on a thin plastic film suspended in argon gas between dual glazing and rated at R-8. New "hard" low-E coatings can also be applied to storm windows. So, low-E main and storm windows can combine to be almost as energy efficient as your walls.

Energy codes require insulated doors and windows with air and heat gaskets around casements in new construction and major renovations. You can replace doors and windows in your older home, but for a price that may not be repaid by energy savings. The best multiple-glazed windows offer a rating of R-8 and cost $150 to $350 apiece. Installation labor can up the cost to $500 per window.

A metal-and-foam—sandwich entry door carries an R-15 rating. If used with a good, airtight dual-glazed wood or metal-and-foam storm/screen door, the entry's R-rating will approximate the wall's. But, such an entry can cost $1,500 or more to install. Also, when replacing any window, check your building code. It may require that old nonwood casements come out, increasing the whole expense.

Using costly high-tech methods isn't the only answer. Jalousies, sunshades, lattice blinds, and awnings also help insulate doors and windows. They are just as effective today as sun and heat radiation barriers as they were in Scarlet O'Hara's day.

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