"TAP" the Sun

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Planning for Available Materials

The collector frame is made of 25-gauge, 4- or 6-inch metal track available from a drywall supplier or contractor. To insure that air moves through the collector without restriction, use the 4-inch material for any TAP that's less than 80 inches high and the 6-inch track for taller units.

Air moves into and out of the collector through metal grilles that run all the way across the top and bottom of the unit, and these too must be large enough to prevent restriction. The height of the grilles should be equal to twice the metal track size: 4-inch track requires 8-inch-high grilles.

Because wall studs will be in the way, however, you'll probably have to use several grilles to cover the intake and exhaust areas. Unfortunately, when you shop for grilles, you may find that the perfect sizes simply aren't available. If you run into this problem, compromise by using the next larger size; you don't want to take a chance of restricting free movement of air through the collector.

Plan and Cut

Many metal structures have horizontal supports called purlins, as opposed to (or in addition to) vertical studs. It's desirable from a structural viewpoint to secure the collector to these members at the top, bottom, or both, if possible. You can find the purlins by looking for horizontal rows of screws that penetrate the exterior metal siding.

Once you've found a likely spot, check inside and out for electrical outlets or other services that might be in the way of the intake or exhaust registers. When you feel certain that you've located an obstruction-free place for your collector, clean the siding in the general area, and mark out the dimensions for the device with masking tape. (Add 1/2-inch to the vertical and horizontal dimensions of the glass to allow for the frame. Thus, the size of a collector with 34-by-76-inch glass will be 34 1/2-by-76 1/2 inches.) Inside this area, mark the duct locations with chalk lines, but be sure to leave about 1 3/4 inches between the frame and ducts to allow for mounting the frame and attaching the 1-inch tabs from the ducts.

For safety's sake, turn off all power before cutting into either the exterior or interior wall. Use a hammer and an old screwdriver to punch through the building's exterior skin within the area where each duct will be located, and then carefully trim out each opening with aviation snips. (Be mindful of razor-sharp metal edges while you're cutting.)

Next, remove the insulation from the duct area, and use a nail or drill to precisely transfer the corners of the duct openings through the interior wall. After double-checking your measurements, trim out the interior drywall or paneling with a razor knife or keyhole saw.

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