Mounts to your outside wall and heats a
standard size room when the sun is out.

Click image to enlarge

The following describes construction of a solar heater that uses free energy from the sun to provide part of the winter heating requirements of homes to which this heater is adaptable. This design is based on a heater built by professor Bruce McQuarrie of Worcester Polytechnic Institute at his home in Auburn, Massachusetts. He estimates that he saved in only two years the cost of the materials to build it.

How It Works

Sun shining through the solar panels heats the air inside the triangular shaped box. As the air inside is heated, it rises to the top of the box and passes into the house through the open window or opening on the first floor. As the heated air moves into the house, it is replaced by cool air moving into the box through the open basement window. There are no moving parts. Leaving the cellar door ajar may aid circulation. A small fan may aid air flow in the house. Some experimentation may be needed.

Is This Solar Collector For You

1. The home must have a south facing (or nearly south facing) outside wall with both basement and first floor windows.
2. There must be unobstructed sunlight on the heater from January to March. If other buildings interfere, this device cannot work. Tall leafy trees which shade the home in summer will not cause much loss of sunlight in winter. However, evergreen tress would be a problem. If obstructing evergreens can be trimmed or removed, you can use this heater. (see Fig.VI).

Construction

The solar heater consists of a floor and two triangular end walls of plywood nailed to both sides of 2 x 4 studding on 16-inch centers. The space between contains insulation. The collector surface, through which the sun shines, consists of two layers of solar sheeting such as Sunlite® HP fiberglass sheeting or Sunlite® HP prefab panels. An access door on one end wall permits entry for maintenance, such as repainting, caulking, etc.

A plywood lid folds over the face of the heater in warm weather. When open, this lid helps reflect the winter sun into the heater.

Figures I and II illustrate the alternative methods of building this passive solar heater. Exact details and measurements are intentionally not shown. The angle of the face of the heat collector varies with the latitude in which it is to be used, so construction measurements will vary somewhat from one area to another.

A professional carpenter or an experienced do-it-yourself home handyman should have no trouble adapting these general guidelines into an actual design for a specific location.

Step 1. Determine the latitude of the home to the nearest even degree. Most highway maps indicate latitude. As a general rule, the slope of the collector face with the horizontal will be an angle equal to the latitude plus 15°. (see inset in Fig. I) This chart is provided for easy reference:

Step 2. Determine where the heater will be placed on the south facing wall. Fig.I illustrates an installation which does not interfere with normal use of the first floor window. Fig. II simplifies construction but prevents normal use of window with heater installed.

The method in Fig.I requires cutting an opening through the wall under the window to admit the heated air.

If it is preferable not to cut through the wall, a detachable plywood "chimney" (which can be removed after the heating season) may be used to convey the heated air into the house through the lower half of the window. This "chimney" should be insulated and sealed around all edges to minimize heat loss.

Step 3. Determine exact position of sloping studs which will support the translucent fiberglass sheet or panel before ordering them. On two concrete blocks, set a 2 x 4 on edge to simulate the position of the level floor. From the height on the outside wall of the house which will mark the upper edge of the heater, stretch a piece of string to form the desired slope angle with the base. (Point A to point B in Fig.I ). The length of the string will determine the length of the sloping studs and the translucent sheets will determine one of the base dimensions. The Fiberglass sheets are available in pre-packaged rolls, 4 feet wide by 8, 10, 25, and 50 foot lengths. One 50' roll should be enough to make a heater 12 feet long with a sloping face of 8 feet, such as in Fig.I

To avoid waste, consider standard dimensions in determining actual construction details. 2 x 4 studs come in 8' lengths. Plywood or particle board sheets come in 4' x 8' feet sheets (check your local supplier for other standard sizes). Roll insulation is designed to fit between studs on 16" centers.

Step 4. If you decide to cut an opening under the window rather than use a "chimney", do this next. The opening should have about the same area as the basement window. Finish off the opening neatly, inside and out. Provide a cover on the inside to prevent cold air leakage at night or during prolonged cloudiness.

Step 5. Construct base of 3/8" plywood or particle board made for outdoor use. Select inexpensive grades. Nail plywood to 2 x 4's on 16" centers and then turn floor over and level it on concrete blocks, shimming until level and evenly supported. Install roll insulation and nail on plywood flooring. Nail vertical studs to side of house to support back wall of plywood (not shown in Fig.I or Fig.II ). Insulate particularly well along cellar wall to prevent heat loss. Nail on plywood back wall.

Step 6. Install sloping 2 x 4 supports. Space them to the exact width of the fiberglass sheets to eliminate cutting the sheets. Thus, the length of the base will be 12' plus the thickness of four 2 x 4's. Nail in end wall studding, providing for an access door in one end. Nail outside plywood panel to studding. Install roll insulation between studs. Nail on inside plywood panels.

Step 7. Install flashing under the shingles or clapboard on house wall at top of heater to prevent water leaks.

Step 8. Nail 1" x 1" strips to lower edge of sloping studs to support inner fiberglass panels. Install panels and caulk the edges with silicone sealant. (see Fig. III) . If you use the chimney method, build and install it before installing fiberglass sheets. Side may be of plywood similar to sidewall construction (with insulation between). The top surface may be made of fiberglass sheets separated by an air space. These sheets will be bend into a curve. (see Fig.IV)

Step 9. Nail a second set of strips to sloping 2 x 4's to support outer fiberglass panel so that panel is flush with upper surface. Caulk edges.

Step 10. Caulk flashing at upper edge of panels to prevent leakage. Nail 1" x 3" strips along edges of loping 3 x 4's to finish off the sloping surface.

Step 11. Make plywood cover to fit between 1" x 3" strips when closed over the heater in summer. Install hinges so it can be opened for winter heating season.

Step 12. Make access door and install. This should be same construction as end walls with insulation between both faces.

Step 13. Paint inside plywood surfaces with flat black to aid in absorbing heat. Do not paint house wall. Paint inner cover surface white to reflect sunlight. Paint outside to match the house color for appearance and protection.

General Notes

To eliminate moisture from condensation between the fiberglass sheets, drill small holes at the bottom of each section for drainage.

Roll insulation should be R-11 foil faced fiberglass insulation. Install with foil towards inside of heater.

Since fiberglass sheets are flexible, install some type of cross supports between the 2 x 4's. Wooden dowels or cross strips of wood may be used. Place them at the one-third and two-thirds points on the sloping 2 x 4's.

Clearance above ground is important to prevent the wood from rotting. Concrete blocks provide about the right spacing.

Clean the surface of the fiberglass sheets as needed. Dirt obstructs the light and cuts down heater efficiency. Plain water is usually sufficient. Remove snow in winter.

Heater works best when basement window is at one end of heater and first floor opening is at opposite end since air must travel further and stay in the heater longer before entering the house. If first floor opening is directly above the basement window, experiment with baffles. (see Fig.V)

Extra heat holding capacity may be gained by installing heat absorbing elements inside the heater. Black painted aluminum cans or metal sheets fastened together may help. This is a chance for you to experiment.