So, you have weatherized and insulated your house. You have switched all of, OK most of your light bulbs to CFL’s and installed a low flow showerhead. Your programmable thermostat is set for 66° at night and you use a whole house fan to cool your house in the summer. Now you are considering entering the world of alternative energy, but you don’t live on a windy five acre lot, nor do you have the funds to invest in a photovoltaic array or a solar hot water system. The answer to your dilemma is a Solar Air Heater.
First you need to determine which window that you want to build your solar air heater for. This type of heater will work in a double hung window, should face south to south west, and should be in direct sun for the greater part of the day. Raise or remove the screen and measure the minimum clear opening width.
If you are using an old window sash, you will need to scrape off any ole paint, repair the glazing putty, prime and paint the sash, and clean the glass.
Build the wood frame: make it 1 ½” wider than the minimum clear opening and 36″ to 48″ tall. Or build it to fit the old window that you are using. Other designs use insulation for the frame, but treated wood decking is much more durable so your air heater will last for years and years. Marine grade plywood or primes and painted 1×6’s may be substituted for the decking.
Add the arms that extend through the window making sure that they extend far enough so that the air heater can be secured on the inside of the window. Follow this up with the remaining decking pieces and the 1×4 trim. Seal all joints with sealant.
Cut the rigid insulation back to fit into the frame, leaving a 5 ½” gap at the top. Use a chalk line to mark the line or a drywall square with a new blade in your knife in order to make clean straight cuts. Secure this into the frame with a continuous bead of construction adhesive. Add 2″ spacers along the edges and in the middle.
Add the horizontal rigid insulation between the arms at the bottom, and then one in the middle of the arms. Again, secure both pieces with a continuous bead of construction adhesive on all four sides.
Cut the front insulation panel and secure with a continuous bead of construction adhesive. Cut the corner bead and secure with roofing nails to the insulation with the fins pointing out. This is a slight modification to the photos shown here.
Paint the entire interior of the solar air heater with flat black spray paint.
Apply the compressible foam weatherstripping along the face of the entire frame. You may elect to use silicone sealant, but this will prevent you from removing the glass in the future.
Secure the old window sash or glass to the frame. Screw directly through the sash to the frame or use 1″ long pieces of aluminum angle to hold the glass in place. Insert a piece of the weatherstripping between the aluminum angle and the glass.
Now you are ready to install your solar air heater and weatherize it so that you don’t loose more heat than you gain. Open the window and set the heater in place. Lower the sash and install foam weatherstripping along the line where the sash will meet the heater. Cut the “air conditioner” foam weatherstipping the width of the sash and insert between the sashes at the bottom of the exterior sash. Next, tuck a piece of plastic wrap between the air heater arm and the window jamb, making sure to secure it in place and cover all surrounding surfaces. Fill the gap between the air heater and the window jamb with expandable foam. Finally, install insulating window film over the window, securing the bottom of it to the horizontal piece of decking.
Finally, cut a piece of rigid insulation to fit in the top opening of the heater to prevent any nighttime heat loss, or roll up an old bath towel and set it into the gap just below the sash. Adding a piece of aluminum flashing on the top of the wood heaters solar air heater will help to keep the water out, and in the spring you might want to prime and paint the treated wood frame.
Materials list: 1 – 4’x8′ sheet of rigid insulation, old window sash or glass, 3 – 5/4x6x8′ treated decking, 1 – 1x4x8′, construction adhesive, exterior sealant, compressible foam weatherstripping or silicone sealant, flat black spray paint, foam sealant (Great Stuff), 3″ screws, 1 ½” roofing nails, metal corner bead (for drywall), aluminum flashing, “air conditioner” foam weatherstipping, 1″x1″ aluminum angle, plastic wrap, and insulating window film. Optional materials: glazing putty, primer and paint.
Tools list: Utility knife, saw, drill, screwdriver, clamps, caulk gun, tape measure, tin snips, chalk line or drywall square. Optional tools: putty knife, paint brush.
Last, but not least, enjoy the free warm heat from the sun and watch your heating bills take a dip. Feel free to contact me if you would like plans, photos and details.