DIY heating systems for greenhouses and hotbeds

• Slope of the furnace chimney — 1.5 cm per 1 m
• Expansion tank volume — 20–30 l
• Temperature elevation (gas heating) — by 4–5 °C
• Heating cable power (UNT) — 1 kW
• Cable trench depth — 400–500 mm

Water, solar, and furnace heating systems

A stable temperature regime in a greenhouse can be ensured by accumulating solar energy or by installing a stationary circuit. In solar heating systems, a storage tank acts as the key component, to which five communication pipes are connected: two from the solar collector, two from internal plate radiators, and one from the water supply network. To minimize heat loss, all supply lines are insulated with cotton wool or felt about 50 mm thick, covered with roofing felt, and secured with wire. The supply of heated water to the plate radiators is regulated by a valve, and their exact number is selected based on the target temperature indicators.

For greenhouses with an area of about 15 m², if constant monitoring is available, furnace heating is effective. The furnace is equipped with a chimney laid under the shelving and an exhaust pipe. To create stable draft, the horizontal section of the chimney is laid with an upward slope of 1.5 cm per 1 m of length. The minimum permissible distance from the furnace walls and chimney to the greenhouse walls and shelving is 15 cm. The massive walls of the furnace accumulate heat, and firewood or fuel briquettes are used as fuel.

A more reliable and easier-to-operate solution is a water heating system. The water-heating boiler is placed in the greenhouse vestibule. Hot water rises through a supply pipe with a diameter of 76 mm, laid under the ridge with a slight slope, and enters the manifold. From there, the heat carrier is distributed through four heating pipes with a diameter of 57 mm located under the shelving, after which the cooled water is collected in the return manifold and returns to the boiler. At the highest point of the system, an expansion tank with a capacity of 20–30 l is installed for water circulation and refilling.

Gas, local, and electric heating

In the absence of a stationary water circuit, gas or kerosene heaters are used, as well as equipment running on liquid fuel. Household gas stoves using liquefied gas are suitable for emergency heating. In small greenhouses, it is convenient to use a tabletop stove with a 5 l cylinder: it is placed in the center of the aisle on a metal sheet, and the combustion intensity is adjusted so that the night temperature in the greenhouse is 4–5 °C higher than the outside air temperature. When using kerosene heaters, metal plates measuring 40×40 cm are placed on wire tripods above them for faster and more uniform air heating.

A fire-safe alternative to an open flame are flameless or catalytic combustion devices. In these, gasoline or alcohol vapors are oxidized by atmospheric oxygen directly on the surface of the heating element in the presence of a catalyst. Heat is released through the chemical oxidation reaction, which eliminates the risk of fire in the enclosed volume of the greenhouse.

If the electrical network can withstand a load of up to 2 kW, air exchange and heating are provided by electric fan heaters, oil radiators, or electric lamps. In greenhouses, only devices with a closed heating coil are allowed. Lamps are suspended over the aisle at a height of 1 m from the surface of the bed with a spacing of 1.5 m, and their total power must not exceed 500 W per section.

For combined air and soil heating, specialized UNT-1 or UNT-2 devices with a power of 1 kW are used. The kit includes a PNVSV heating wire 66 m long, a circuit breaker, and a two-pole socket with grounding. The installation of the heating wire in the soil is performed in a strictly defined order.

1. Dig a trench 400–500 mm deep.
2. Pour a layer of expanded clay or crushed stone 40–50 mm thick and a layer of sand 50 mm thick.
3. At the end walls of the trench, lay wooden templates made of timber with a cross-section of 40×40 cm with slots every 100 mm.
4. Lay the heating wire into the slots of the templates in accordance with the diagram.