How to Construct a Passive Solar Heater
Using free sunlight to help heat your home, garage or shed is both green and thrifty. These techniques use modern solar ideas as well as building concepts understood by Indians in the southwest well before contact with Europeans.
Building a passive solar heater can use household discards such as beer or soda cans. Workshop tools and some basic carpentry skills will give you a heater which uses no fuel, but will take the chill out of a garage, shed or help in a sun-exposed room.
Couple your passive heater with a few simple passive solar heating design ideas, such as a water wall to "charge up" with heat during the day to release at night and you will increase your supply of "free" heat.
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Things You'll Need
- 2 by 4 lumber
- Wood saw
- Nails
- Hammer
- Power Drill
- 2-inch hole saw blade
- High-temperature flat black paint (grill or stove paint)
- Aluminum (soda and/or beer) cans
- 1 1/4-inch metal drill bit
- Duct tape
- High temperature liquid or paste adhesive (rated to 200 degrees F or greater)
- Clear silicone sealant
- Clear plexiglas sheet
- Outdoor caulk
- Caulking gun
Instructions
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Cut your 2 by 4 lumber into lengths to make as large a frame is practical for your exposed wall space. Your heater will not overheat the shed or room. Choose a size you can mount on the wall which won't block windows or doorways.
Nail the frame together and nail the plywood to completely cover the back.
Use your hole saw to cut 2-inch holes at the top and bottom (center) of the plywood back (inside the frame). Evenly space these top and bottom holes, one per 2 feet, if your frame is four feet or wider. These will be the cool air inlet (bottom hole) and warm air outlet (top hole).
Place the assembly against the wall. Mark the wall to match your inlets and outlets. Set the frame aside and cut the wall to match inlet and outlet holes.
Paint the frame interior and sides (the back only needs a sealant such as Water-Seal) with flat black stove paint. Set aside to dry.
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Drill a 1 1/4-inch hole in the bottom of each of your empty, clean soda (or beer) cans. Tops should already have a hole from opener.
Stack one can on top of another can and seal them together with duct tape. Make a column of these stacked cans tall enough to fill your frame, minus about 4 inches for an air gap above and below the column when it is mounted in the frame.
Repeat the process to make enough columns to loosely fill the width of the frame.
Paint the columns with flat black stove paint and set aside to dry. These baffled columns will heat as sunlight is absorbed by the black aluminum cans. The air inside will heat and rise (through convection) up the column and out through the (top) outlet hole in the back of the frame. Cool air will be drawn in through the (bottom) inlet hole to be heated and continue the cycle. The holes in the cans will pass the air up slowly as the smaller top and bottom holes in each can restrict the movement and add to the air heating time.
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Lay the frame on a flat surface.
Use high temperature adhesive to glue the columns onto the interior of the frame. Be sure to leave an air gap of at least two inches above and below each column.
Glue the plexiglas face onto the frame. Be sure the seal is continuous and complete so no heated air escapes (or cold air is allowed to leak in).
Allow to dry completely.
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Mount the heater, making sure to align inlets and outlets with the holes you cut through the building wall.
(Option: Use lengths of 2-inch PVC pipe to pass completely through the wall and extend an inch into the heater assembly. This will add strength to the connection and provide a better seal.)Use outdoor caulk or silicone sealant around the frame to provide a tight seal and prevent any air leaks into the building.
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Tips & Warnings
If practical, place a black plastic or metal water drum inside your building where it will receive direct sunlight through most of the day. This water will act like a thermal capacitor, storing heat as the drum absorbs sunlight and releasing that heat slowly after the sun sets.
You may add a small fan at the inlet hole to the heater to increase the flow of air into the heater. This changes the heater from purely passive to being an active solar heater.
References
Resources
- Photo Credit sun rays image by Konstantin Gusev from Fotolia.com
