A climate battery stores daytime solar heat underground and releases it overnight — no boiler, no propane, no electricity bill.
A climate battery is a ground-to-air heat transfer (GAHT) system. It uses the thermal mass of soil and gravel beneath your greenhouse floor to store surplus solar heat during the day and release it back into the growing space overnight.
On a sunny day, your greenhouse interior can reach 30-40°C while the outside temperature sits at 5°C. A small inline fan pushes this warm, humid air down through a manifold pipe and into a network of perforated drainage pipes buried in a gravel bed 400-600mm below the floor surface. As the air passes through the gravel, the stone and surrounding soil absorb the heat. The air exits the other end of the loop cooled and dehumidified — reducing overheating and condensation problems at the same time.
After sunset, the stored heat radiates upward through the soil and floor into the greenhouse. The thermal mass acts like a slow-release heater, raising overnight temperatures by 3-8°C compared to an unheated greenhouse. In mild coastal BC climates, this is often enough to keep a greenhouse above freezing through winter without any supplemental heat.
As warm humid air passes through the cool underground gravel, moisture condenses on the stone surfaces. This captured water drains through the gravel bed and recharges soil moisture below the greenhouse. The result: lower humidity inside (reducing disease pressure on plants) and passive sub-irrigation of planting beds.
Cross-section view — not to scale. Perforated pipes shown as dashed lines, solid manifold risers at each end.
Enter your greenhouse dimensions and conditions to calculate gravel volume, pipe layout, fan sizing, and a full materials list.
Total interior floor area. A 20x25 ft greenhouse = 500 sq ft.
Affects winter design temperature and recommended insulation depth.
Solar DC fans are ideal — they run hardest when the sun is strongest, which is exactly when you need the most heat transfer.
These steps assume a new greenhouse build or a major retrofit where you can access the full floor area. If retrofitting an existing greenhouse, you may need to work in sections.
Remove soil to a depth of 600-750mm across the full greenhouse footprint. Set excavated soil aside for backfill around the perimeter later. Grade the bottom with a slight slope (1-2%) toward one end for condensation drainage. If your water table is high, install a sump or French drain at the low point before proceeding.
Use a plate compactor or hand tamper to firm the excavated base. You want a stable surface that will not settle unevenly under the weight of the gravel. Check for level across the full area with a string line or laser level. The drainage slope should be consistent, not pooling.
Roll out non-woven geotextile fabric across the entire floor and up the sides of the excavation. Overlap seams by at least 300mm. This prevents soil migration into the gravel bed while allowing moisture to drain downward. Secure edges temporarily with staples or gravel.
Spread 150mm of clean, washed drainage gravel (20-40mm diameter) across the full floor. Level with a rake. Do not use crusher dust or fines — air must flow freely through the gravel. Compact lightly to settle.
Lay out your perforated drainage pipe in parallel runs across the length of the greenhouse. Space pipes evenly (typically 300-500mm apart depending on your calculator results). Perforations face down. Connect all pipes at each end to a solid manifold pipe that runs across the width of the greenhouse. Use sweep elbows, not sharp 90-degree fittings, to reduce airflow resistance.
Cover the pipes with the remaining gravel to reach your target depth of 400-600mm total gravel bed. Work carefully to avoid displacing pipes. Level the surface. The pipes should be fully surrounded by gravel on all sides with at least 100mm of cover above them.
Roll out a second layer of geotextile over the top of the gravel bed. This prevents soil or mulch from migrating down into the gravel and clogging air passages. Overlap seams 300mm. This layer is critical for long-term system performance.
Run solid (non-perforated) pipe from each manifold up through or along the foundation wall to above floor level. The inlet riser connects to the fan. The outlet riser vents cooled air back into the greenhouse at the opposite end. Cap both risers with a screen or mesh to keep debris and rodents out.
Mount your inline fan at the inlet riser. For solar DC fans, mount the panel on the greenhouse exterior at an angle to catch maximum winter sun. For AC fans, wire to a thermostat set to activate at 25-28°C — the fan only runs when there is surplus heat to store. Passive convection systems skip this step but provide significantly less heat transfer.
Add 100-150mm of topsoil or growing medium over the upper geotextile if you are planting directly in the floor. For a gravel-floor greenhouse, the upper geotextile is your finished surface. For concrete slab greenhouses, pour your slab over the upper geotextile. The slab acts as additional thermal mass and radiates heat effectively.
Install rigid foam insulation (minimum R-10, 50mm XPS or EPS) vertically around the inside perimeter of the excavation from grade down to the bottom of the gravel bed. This prevents heat from leaking sideways out of the thermal mass. Backfill soil against the exterior of the foundation wall for additional insulation. In Interior BC, extend insulation to R-15 or deeper.
Run the fan and verify airflow from both the inlet and outlet risers. Place thermometers at the inlet, outlet, and at floor level in the center of the greenhouse. On a sunny day, you should see a 5-15°C temperature drop between inlet and outlet air. Log temperatures daily for the first two weeks. If the outlet air is not cooling significantly, check for pipe blockages or fan sizing issues.
Most climate battery materials are standard drainage and landscaping supplies available across BC. Here is where to look.
Available at Home Depot, Slegg Building Materials, and most building supply yards in 4" and 6" diameters. For 8", check irrigation or agricultural suppliers. Buy corrugated perforated drainage pipe (not sewer pipe).
Order 20-40mm washed drain rock from any aggregate supplier. On Vancouver Island: South Island Aggregates, Upland Excavating (Courtenay), or local sand and gravel pits. Sold by the cubic yard — order delivery for anything over 2 m³.
Non-woven landscape fabric in wide rolls. Available at landscape supply stores and building centres. Avoid the thin weed-barrier fabric from garden centres — you need proper geotextile rated for drainage separation.
Solar DC inline fans: order online from greenhouse or off-grid solar suppliers (e.g. Solar Blaster, AC Infinity solar models). AC inline duct fans: available at Home Depot, Canadian Tire, or HVAC suppliers. Match CFM to your calculator results.
2" XPS (extruded polystyrene, blue or pink board) from any building supply. Slegg, Home Depot, Windsor Plywood all stock it. For Interior BC, double up to 4" or use higher-R polyiso board.
Sweep elbows, couplers, and tee fittings for corrugated drainage pipe are stocked at most building supply yards. Bring your pipe diameter. If you cannot find sweep elbows, use two 45-degree elbows to make a gentle 90.
A climate battery works best when designed alongside your greenhouse from the start. We can help with site prep, excavation, and system sizing.