Heating a Homemade Greenhouse

Metal drums in a greenhouse can capture the sun's heat.

There are many ways to heat a greenhouse. One of the more popular methods is to use a passive solar energy system. It is relatively inexpensive to build, works well in most climates (but not in extreme temperatures), and costs nothing to use. The system collects the sun's heat in 55-gallon water drums during the day and slowly releases that heat during the cooler evening.

Things You'll Need

• 55-gallon metal drums filled with water
• Weather stripping
• Flexible sealant
• Polyethylene sheets
• Rigid insulation sheets
• Plywood sheets

Instructions

1. Install weather stripping around the door and vents of the greenhouse. Apply flexible sealant around the joints between the walls and the roof.

2. Line the interior of the walls with polyethylene sheets. For added flexibility, install the sheets as hanging curtains that are weighted at the bottom. The sheets can then be rolled up during the day.

3. Cover the inside of the greenhouse's north wall, where most of the heat escapes, with rigid insulation sheets. You can hang the sheets on hooks for easy removal during the day.

4. Lay rigid insulation on the greenhouse floor. During the winter, heat escapes through the cold floor. For added strength, cover the insulation with sheets of plywood.

5. Calculate the number of 55-gallon drums that you'll need to heat your greenhouse. A working formula is to use 2 gallons of water for each square foot of the greenhouse's southern wall, which passes sunlight to the drums. For a greenhouse with a southern wall that is 12 feet long and 8 feet high, for example, the total square footage is 96. Apply the formula to get 96 x 2, which equals 192 gallons of water--an amount that can easily be stored in four 55-gallon drums.

6. Paint the steel drums black to attract the maximum amount of heat. Stand them up inside the greenhouse as close to its southern wall as possible, and fill them with water. You can cap the drums to retain the water or leave them open to add humidity. Replenish evaporated water as needed.

Tips & Warnings

• Variations of the free-standing-drums method include storing sealed drums horizontally on metal shelves, or stacking them vertically. Heat-collecting devices can also be made out of concrete-filled cinder blocks, stacked bricks, stones, adobe, or any other material that attracts heat during the day and releases it during the cooler evening hours.

References

• Free Stuff Me: Free Solar Lean-To Greenhouse Plans
• Frugal Living Freedom: Build a Homemade Greenhouse ...