The Univent Automatic Vent Opener by Ken Bar is a passive, no-electricity way to automate greenhouse ventilation, often sold as a solar vent opener because it runs on the sun's heat. A sealed wax cylinder expands with heat and pushes an aluminum shutter vent open as the greenhouse warms; when the air cools, the wax contracts and the vent closes. No wiring, no power draw, and nothing to switch on.

The kit includes the hardware to mount directly to a shutter vent. It lifts up to 33 lbs, enough to drive a heavy aluminum shutter. Set the activation temperature between 60°F and 70°F by turning the cylinder, with the vent reaching fully open by 86°F. For shutters 30 inches and under, one opener is enough; for larger shutters, use two for even operation.

Because it runs on ambient heat rather than electricity, the Univent is a reliable choice for off-grid high tunnels and greenhouses that need passive, hands-off temperature control.