Before the advent of. electric air conditioners, homeowners used an array of simple tactics to beat the heat. They pulled the shades on the sunny side of a house (but left the upper sash of double- hung windows open), then opened both the shades and windows on the shady side, and turned on fans that stirred cooling breezes.
These battlers of the heat had an instinctive appreciation of at least three complex cooling processes. In the jargon of today’s energy pioneers—whose interest in old-time cooling methods has been sparked by the quest for lower utility bills—the processes would be identified as preventing solar gain (pulling the shades), facilitating personal evaporative cooling (letting breezes cool your sweat- dampened skin), and utilizing thermo siphoning and active ventilation to augment air flow (lowering upper window sashes, providing vents in the attic and turning on fans).
Of these processes, only thermosiphoning is difficult to understand.
Thermosiphoning is based on the principle that heat rises, if windows near the ceiling of a room—or vents near the top of the house—are open, the rising hot air will waft outside. As this air leaves the house, it will be replaced by cooler air sucked into open windows on the shady side of the house or crawl-space vents near the cool ground. To take fullest ad vantage of thermosiphoning, open the lower sashes of windows on the cool side of a room about 25 percent less than the upper sashes of the windows on the warm side. The restricted passage on the cool side creates a natural pressure that actually pulls the air in faster, in creasing evaporative cooling.
On a smaller scale, at individual windows, thermosiphoning sometimes has a negative effect that must be avoided. Between loose-fitting draperies and the in side of a window is a space that collects hot air on sunny days. When this air rises, it pulls cooler air up under the fabric, creating a convective current that circulates the hot air into the room. A valence of fabric or wood installed across the top of the window will reduce this flow.
On a scale larger than the treatment of individual windows, thermosiphoning can be used to encourage air flow throughout an entire house. Gable and soffit vents have long been used to flush unwanted heat out of attics, and glazed cupolas—especially popular atop homes in New England—provide a similar siphoning service for the highest living space of a house. Today many homeowners are duplicating the effect of the cupola with a plywood and plastic shaft, called a solar chimney.
In a solar chimney, sunrays heat the air through glazed southern and western faces; the heated air rises quickly out of the chimney top, pulling heated air out of the house in its wake. A wind-driven turbine, capping the chimney at the top, can further increase the air flow when the wind is blowing. As the heated air exits from the top of the house, cooler air is pulled in through floor registers from the basement or crawl space, and through windows opened to shaded porches or gardens.
For maximum efficiency, solar chimneys should be positioned on an unshaded expanse of roof that receives full mid day and afternoon sun. Choose a portion of the roof offering a straight descent through the attic to a room below, free of intervening beams, heating ducts or electrical cables. If necessary, remove a section of attic flooring to make an inspection before proceeding.
For the body of the chimney, you will need standard, construction-grade, 2-by- 4 studs and 1 exterior plywood. You can use the same plywood to fashion sliding doors for the ceiling below, which are used to close off the opening in cooler weather. Transparent, fiber-reinforced plastic panels ¼ inch thick, sold under the trade name Fiberglas, are used to glaze two sides of the upper portion of the chimney. A standard 16-inch wind- turbine vent is set atop the chimney. All of these materials are available at large building-supply stores.
The turbine requires a square chimney cap, however, which is not standard. Take the turbine to a sheet-metal worker to have a cap built to the dimensions of your chimney—15½ inches square for houses that have rafters or roof trusses spaced 16 inches apart, 23½ inches square for roofs based on 24-inch spacing. The cap should have a down-turned lip around its perimeter and an upturned collar at its center to accommodate the turbine. To prevent water from leaking through the joints of the chimney, you also will need lengths of aluminum flashing, 4, 8 and 18 inches wide.
Silicone caulking and asphalt roofing cement finish the job outside, sealing all the rooftop seams. To seal the inside, you need two lengths of U-shaped aluminum channel, each 1½ inches wide and twice the length of the ceiling opening below the chimney (Step 1). Also buy rigid foam insulation, 1 inch thick, to glue to the back of the sliding doors.
As with any building project, check with your local building department be fore you begin work; in many communities, local building or architectural codes strictly regulate the design and position of rooftop additions. In addition, you may have to obtain a building permit.
New Look at an Old Friend
A tried and true ventilator, the electric, paddle-style ceiling fan has been in use in warm climates for more than 100 years. Today it’s gaining renewed favor in areas where the cost of electric air conditioning has sky-rocketed. In warm weather, the fan circulates standing room air, pulling cool air from the floor of a room and washing it over the room’s occupants. In winter, the same fan can force warm air that has risen back down into the living space.
A ceiling fan may be equipped with adjustable paddles; reversing the pitch of the blades reverses the flow of air. More convenient are models that have a reversible motor, which spins the blades in one direction to force the air flow up, in reverse to push it down. Additionally, most fans have variable- speed motors that let you slow the fan for gentler, draft-free downward circulation of warm air, or speed it up for a brisker, high-speed current for cooling. Paddle fans can be mounted on any flat or gently angled ceiling that is at least 7 feet high. Most fans are installed in the same way as a hanging pendant light fixture, hooking over a metal strip on the bottom of an electrical ceiling box. For heavier models a box with a threaded stud must be installed. Most manufacturers provide instructions for installation and hardware matched to each model of fan they sell.
An air-cooled house. Cool air enters this house through crawl-space vents, passing through floor registers into the living spaces. Windows, open at the top on one side of the house and at the bottom on the other, augment the natural crosscurrent with a thermally siphoned flow. Windows exposed to the south are shaded with exterior awnings on the first floor to keep out the sunlight; windows on the upper floor are shaded by the roof overhang.
Increasing the air flow through the whole house are an attic exhaust fan, mounted in the ceiling of an upper-story room, and a solar chimney, which expels heated air out of the house from the highest point. Air circulation through the attic is provided by louvered gable vents at each end of the house and soffit vents underneath the eaves. A paddle-style ceiling fan over the dining area and strategically placed portable fans create additional cooling breezes.
Making the Most of Air Currents
CRAWL-SPACE VENTS
Building a Solar Chimney
1. Cutting the roof opening. Inside the attic, drill a locating hole through the roof next to a rafter to mark the position of one upper corner of the chimney. Measure the distance between the rafters. On the roof, find the locating hole, then use a linoleum knife to remove shingles from an area 2 inches larger than the planned chimney. From the locating hole, draw a cut line parallel to the roof ridge and as long as the distance between rafters.
Place the chimney cap with its upper edge on the cut line and level it with scraps of wood. Hold a carpenter’s level plumb at the corners of the cap closest to the eaves and mark their locations on the roof. Make a second mark ¾-inch up the slope from each of these corner marks. Draw a straight line between the new marks and between each end of this line and the first cut line. Cut along all four lines with a saber saw.
2. Framing and enclosing the inside shaft. Nail two short 2-by-4 boards,
called headers, between the joists just outside the marks. Cut four 2- by-4
studs long enough to reach from between the joists to a point at least 1
foot above the level of the roof ridge. At the intersections of the headers
and joists, nail the studs to the joists. Then nail the studs to the rafters. 
If the rafters and joists are offset, and not one directly above the other as in the truss roof shown here, you will have to use shims and blocking at the joists to keep the studs plumb.
Drill four holes down through the ceiling at the corners formed by the studs and headers. Finally, nail plywood to the outsides of the studs to enclose the chimney within the attic.
3. Building the rooftop section. To make sup porting frames for the plywood and the plastic glazing, nail four short 2-by-4 spreaders horizontally between the studs at the top. Add a second set—also horizontal—where the chimney passes through the roof. Enclose the entire north and east sides of the chimney with ½-inch exterior-grade plywood; then, using the same kind of plywood, enclose the lower portion of the south and east sides up to the middle of the bottom spreaders. Note: Use only aluminum or galvanized nails any place where the nailheads will be exposed to the weather. Paint all of the interior surfaces of the studs, spreaders and ply wood with flat black, oil-base paint.
Hang a plumb bob f each corner of the roof opening. Have a helper mark where the bob touches the joists below and cut away the insulation between the marks.
4. Glazing the sunny sides. Cut two sheets of plastic glazing to the exact size of the south and west sides of the chimney. Drill screw holes inch in diameter at each corner of the sheets and at 12-inch intervals around the perimeters. After mounting the roof, brace the glazing against the chimney frame and drill 1/16-inch pilot holes into the wood through each hole in the plastic. Set the plastic aside and apply a thick bead of silicone caulking to the frame. Return the plastic to the frame and secure it with round- head wood screws.
To seal the corners, cut four lengths of 4-inch- wide aluminum flashing to the height of the chimney at each corner. Bend each piece in the middle lengthwise and attach it to the corners of the chimney with round-head aluminum screws spaced every 6 inches.
5 Flashing around the chimney. Cut an 8-inch strip of flashing 8 inches longer than the width of the side of the chimney closest to the eaves. Bend the strip in the middle lengthwise. Place the Strip at the Joint and cut 4 inches into the bend at each end with tin snips (above, left). Bend the vertical tabs created by the cuts sharply around the corners of the chimney; insert the horizontal tabs under the shingles at the ends. Secure the flashing to the roof with roofing nails. Don’t nail the flashing to the chimney. Similarly cut and emplace flashing along both of the slanting sides, inserting the horizontal edge of the metal under the shingles at the sides.
Remove two rows of shingles above the remaining side of the chimney. Cut an 18-inch strip of aluminum 12 inches longer than the width of the chimney. Bend the Strip lengthwise, 4 inches from one edge. Make 6-inch cuts into each end along the bend and install the strip with the 4-inch portion vertically against the chimney. Bend the tabs around the chimney as before, and insert the horizontal edge of the metal under the shingles above the joint. Carefully bend back the shingles to nail the metal directly to the roof (above, right). Replace one row of shingles, inserting and nailing them under the shingles above them. Seal all of the nailheads and seams with roofing cement.
6. Completing the flashing. Cut lengths of 6- inch flashing for the four sides of the chimney, each long enough to extend 6 inches around the corners (inset). At the side closest to the eaves, hold the flashing against the chimney with the bottom edge of the metal ¼ inch above the flashing installed in Step 5. Bend the ends around the corners and fasten the metal to the chimney with roofing nails. In the same way, attach flashing to the sloping sides. Then install flashing on the uphill side of the chimney, bending its ends to overlap the side pieces. Seal the nailheads and joints between the metal and the chimney with roofing cement.
7. Installing the turbine vent. Fit the chimney cap onto the chimney top and nail it to the two plywood sides. On the remaining sides, drill through the metal and the plastic, and secure the cap with screws. Fit the round base of the turbine vent onto the collar of the chimney cap, joining the two with sheet-metal screws. Finally, rotate the adjustable rings at the base of the vent to straighten the turbine.
Paint the wooden sections of the chimney to match the exterior trim of the house; then, after allowing at least 48 hours for the paint to dry, seal the seams at the base of the chimney cap with silicone caulk.
Adding the Access Doors
1 Cutting the opening. Connect the four locating holes drilled in Step 2 to out line the ceiling opening and, wearing safety goggles and dust mask, cut along the lines with a keyhole saw. Join four 1-by-4s to make a frame that will just fit into the opening, and se cure the frame to the faces of the headers and studs with finishing nails.
With a hacksaw, cut 1½-inch aluminum U channeling—so called because of its U-shaped cross section—to twice the length of the opening. Drill 3 holes every 6 inches along the side of each channel and screw the channels through the ceiling into the headers. The open sides of the U should face each other across the ceiling opening (inset, bottom left).
2 Inserting the doors. Cut a plywood rectangle 1 inch larger than the size of the ceiling opening. Glue rigid foam insulation onto the back of the plywood. Cut the panel exactly in half with a circular saw. Bore %-inch holes in both pieces at each end and insert finger pulls. Push channel caps into the channels at one end and slide both door sections into the channels from the other end. Add a second set of channel caps to keep the doors from sliding out.
Tapping the Coolness of a Crawl Space
Adding a floor register. From the crawl space or basement, find an area clear of any electric wires or plumbing pipes that would interfere with the opening for the new register. Drill a locating hole straight up through the floor next to a joist in the clear area. In the room above, put the register on the floor with one corner on the locating hole. Trace around the base collar of the register with a pencil, then cut out the outlined area with a saber saw.
Set the register into the opening and push it down until the cushioned flange underlying the grate lies flat on the floor. Secure the register with wood screws at each corner.