Do-it-yourself polycarbonate greenhouse heating

A greenhouse in the climate is necessary in order to plant seedlings, protect them from the vagaries of spring weather, and move mature plants to the garden as early as possible. And you can grow anything in a greenhouse all year round, even on an industrial scale. 

The further north the latitude, the more acute the owner of the greenhouse faces the issue of maintaining heat. Moreover, it is important to warm up both the air and the soil evenly and preferably at the same time.

The editors of the KP have collected and analyzed various heating options for a polycarbonate greenhouse and offer the result of their research to the attention of readers.

What is important to know about heating polycarbonate greenhouses

The table contains information about commonly used methods of heating polycarbonate greenhouses.

Pros and cons of polycarbonate greenhouses

Polycarbonate is becoming more and more popular as a material for building greenhouses. The reason for this lies in its many positive qualities.

• There are on the market sheets of various sizes, which allows you to build a greenhouse of any size, from several containers with seedlings to large agricultural production.
• Light transmission polycarbonate reaches 92%. That is, the sun’s rays effectively heat the internal volume of the greenhouse and supply the plants with the necessary ultraviolet.
• Non-flammable polycarbonate. Its melting point is +550°C without the release of hazardous gases.
• Inside the greenhouse it is possible to build partitions, doors, vents.
• Polycarbonate retains its properties at temperature range from -40 to +120°C.
• The honeycomb structure of polycarbonate provides high-quality thermal insulation.
• Modern grades of polycarbonate 200 times stronger than glass. The material withstands strong wind and hail.
• Polycarbonate do not harm chemical detergents and acid rain.
• Greenhouse construction does not require special tools and can be done by hand.

Disadvantages polycarbonate as a building material:

• End faces of sheets of cellular polycarbonate must be closed special polycarbonate profile. If moisture gets inside, fungal spores, molds, insects, then the light transmission of the material will drop sharply.
• In winter, the roof of the greenhouse is needed regularly clear snow. If this is not done, then under its weight the sheets may be deformed, and gaps will appear between them.
• In summer, a greenhouse is necessary wash regularly for cleaning from settled dust and dirt. This is done in order to restore light transmission.
• Polycarbonate does not burn, but melts at a temperature of about 500 °C. Even a fire kindled nearby can deform the greenhouse, and coal from it can make a hole in the greenhouse.
• Polycarbonate is hard to break, but easily damaged by a sharp object, for example, a knife.

Polycarbonate thermal insulation

It is desirable to thermally insulate the greenhouse with any method of heating, although the air in the cavities of cellular polycarbonate is already an excellent heat insulator in itself. The weight of polycarbonate is 6 times less than that of glass, and the heat transfer coefficient is noticeably lower. This indicator characterizes the amount of heat passing through each square meter of the surface separating environments with different temperatures. For construction, just a lower value of this value is needed. For example, for glass with a thickness of 4 mm, this figure is 6,4 W / sq. m ° C, and for cellular polycarbonate of the same thickness, only 3,9 W / sq. m ° C.   

This is true only if the polycarbonate sheets are correctly mounted and their end faces are sealed. In addition, a bubble polyethylene film, which is covered from the inside, will help to minimize heat loss. the bottom of the walls of the greenhouse, but not the roofso as not to block the sunlight.

The main methods of heating polycarbonate greenhouses

There are many options to increase the temperature of the air and soil in the greenhouse. The choice of a specific option depends on the required heating parameters, the technical and financial capabilities of the owner of the structure.

Electric heating

Increasingly, electric heaters of various designs are used as a heat source. It can be:

• Thermal cable, heating soil;
• infrared emitters;
• Heat guns heating the air;

Pros and cons of electric heating

The undoubted advantages of this method of heating is the ease of installation and connection to a conventional outlet. But there are also disadvantages: it is impossible to simultaneously heat the air and the ground, because thermal cables heat only the ground, and heat guns only heat the air. You can, of course, connect both types of heating, but the load on the network will be huge, and electricity bills will be cosmic. It is necessary to waterproof all elements of the system or install an exhaust fan to get rid of excess moisture. In a large greenhouse, you need to install several heaters.

Heating cable

Heating with a thermal cable is effective and safe. Installation of a heating system with a self-regulating heating cable is simple. It is only necessary to carefully follow the instructions and ensure protection against excessive moisture in the soil in advance. 

A self-regulating cable thermostat is optional, but highly recommended as it further reduces energy costs. The sequence of installation of a self-regulating thermal cable and a warm floor is almost the same and is described below.

Step-by-step instructions for connecting electric heating

Installation of a self-regulating thermal cable in a greenhouse is carried out in the following sequence:

• The first step is to dig a pit up to 0,5 m deep, on the bottom of which foam plastic or similar heat-insulating material is laid.
• A thermal cable is laid out over the thermal insulation layer with a certain step (see the manufacturer’s instructions). All connections are carefully sealed. A layer of sand 5 cm high is poured on top and a stainless steel mesh is laid to protect the cables from damage by shovels or choppers.
• The last operation is filling the pit with soil and planting seedlings. 

Heat guns and heat pumps

Large fan heaters are commonly called heat guns. The flow of heated air is actively driven throughout the entire volume of the greenhouse, evenly distributing heat over the plants. This method is widely used in agricultural enterprises, but it is too expensive for a home greenhouse. And the equipment is expensive and needs to be installed with the help of specialists.

A heat pump is a heating technology using natural heat, its concentration and direction to the coolant. A high-quality heat pump produces up to 5 kW of heat, while consuming up to 1 kW of electricity. The principle of operation of the device is the same as that of an ordinary refrigerator, where the heat taken by freon from the products placed inside heats the external radiator, dissipating in space. But the heat pump uses this heat to heat water in the greenhouse’s heating system. 

The system is economical and reliable, but requires initial costs for drilling wells to a depth below the soil freezing limit, installation and commissioning of equipment with the involvement of specialists. But the costs quickly pay off: such systems consume little electricity compared to electric heating with infrared emitters or heat guns.

Gas heating

Today, greenhouse heating systems using gas heating are still popular.

Pros and cons of gas heating:

Gas convectors

Under the decorative casing of the gas convector there is a burner and a heat exchanger completely covering it. The temperature in the room rises due to the spread of warm air heated by the burner. No water circuits are required.

The composition of the gas convector includes the following elements:

• Heat-resistant case;
• Heat exchanger for warming the air;
• Gas burner inside the heat exchanger;
• Gas pressure regulating valve;
• Smoke removal system;
• Thermostat that controls the microclimate;
• Control automation. 

Gas-burners

The gas portable heater is a ceramic plate, which is heated by a burner placed behind it. Air is heated by contact with red-hot ceramics. A protective mesh is installed in front.

This heater consists of the following parts:

• Cylindrical body with built-in gas cylinder;
• Hose connecting the cylinder to the burner;
• Protective grid and gas burner umbrella.

Step-by-step instructions for supplying gas to the greenhouse

Important condition: do-it-yourself connection to the gas pipeline is strictly prohibited. This can only be done by gas service specialists. 

The bottled gas heating system is installed in the following sequence:

The burner installation site is selected according to the following rules, prescribed in most operating instructions:

• Distance to soil 1 m;
• Distance to plants 1 m;
• The distance between burners or convectors is at least 0,5 m.
• A forced ventilation system is mounted above the burners;
• The heaters are connected by a hose or pipe to a gas cylinder or to a branch from a gas main. Connections are carefully fixed with clamps.

Heating greenhouses with sunlight

The most natural way to heat greenhouses is sunlight. In the southern regions of Our Country, it is quite enough to provide the desired microclimate in the greenhouse.

Natural heating by sunlight

If you plan to operate the greenhouse year-round, then the easiest way to increase the efficiency of solar heating is to build a roof with a slope towards the south. The side walls of the greenhouse can be sheathed with reflective material, foil inside. This will not allow the sun’s rays to leave the internal volume of the room, where they will give up all their heat.

Heating with solar panels

We are talking about the most modern way to generate electricity – solar panels. They can cover the roof of the greenhouse and heat it with the received environmentally friendly energy. 

There are complete sets (solar power plants) on the market, as well as individual structural elements: Energy can be stored in batteries and heat the greenhouse at night. This method has only one drawback – the high cost of equipment. 

There is no universal installation scheme, the connection is carried out in accordance with the instruction manual for each product.

Much cheaper are the so-called solar collectors, which store solar energy in the form of heated water or air. They are mass-produced, but summer residents often turn an old cast-iron heating radiator into a solar collector, painting it black. Or they lay a water hose coiled in rings on an opaque roof. But there are more advanced schemes of such devices.

Step-by-step instructions for installing solar collectors

• The bottom is mounted on a metal frame, it is thermally insulated;
• Pipes with water or air are laid and fixed on the thermal insulation;
• The pipes are connected into a single system for the circulation of the coolant;
• The entire structure is covered with a transparent lid.

Helioconcentrators and solar panels are placed on the roof of the greenhouse. Craftsmen also construct such structures that automatically rotate after the Sun moving across the sky. The manufacture of such a “gadget” will require a lot of work and time, but as a result, the owner of the greenhouse receives an almost inexhaustible source of thermal energy.

Pros and cons of natural solar heating

Water heating of greenhouses

The principle of operation of water heating is known to all. But in a greenhouse, hot water does not move through radiators that warm the air in the room, but through pipes laid in the ground below the roots of plants.

Pros and cons of water heating

Step-by-step instructions for installing water heating greenhouses 

Installation of water heating is similar to installation of heating with a thermal cable.

1. Trenches for pipes are dug in the floor of the greenhouse at a depth of up to 0,5 m;
2. Thermal insulation is laid at the bottom, most often polystyrene foam;
3. Pipes are laid on insulation and connected into a single system;
4. From above, the pipes are covered with a layer of sand up to 5 cm thick;
5. A coarse steel mesh is laid on the sand;
6. Fertile soil is poured over the grid;
7. Seedlings are planted.

Furnace heating of greenhouses

No technical progress cancels the traditional furnace heating of the greenhouse. It is especially popular in wooded areas that do not have a stable gas and electricity supply. The so-called “potbelly stove” can always be built from improvised materials and installed in a greenhouse. Serially produced more advanced models with ribbed surfaces. The disadvantages of this method are obvious: it is the need for constant supervision and a high fire hazard. But the soil does not warm up.

Warming of the foundation

Polycarbonate manufacturers claim that greenhouses made from their materials do not need a foundation due to their low weight. This is true, but only partial. 

The foundation is necessary for the greenhouse to prevent heat loss through the ground. It is enough to make a shallow strip foundation of concrete with insulation from the bottom and sides with extruded polystyrene. Fine gravel and sand are poured inside the resulting box to level the floor and form drainage. 

After that, you can proceed with the installation of the selected heating system. If it is not there, then the soil is filled up and plants are planted.

Biological heating

Another option for natural heating of the greenhouse. For its implementation it is necessary:

• Remove the top fertile layer;
• Fill the resulting recess to a third of the depth fresh horse manure;
• Put the soil back in place.

The manure temperature is 60-70°C for 120 days. A bonus is the additional top dressing of the roots of the plants. Humus is not suitable for such insulation, it quickly loses heat. A huge minus is that it is difficult to find and deliver fresh manure in the right amount.

How to choose the best option for heating a greenhouse

 Factors to consider when choosing a heating system:

• Purpose and dimensions of the greenhouse;
• Option for heating a residential building near a greenhouse;
• heating budget;
• Features of heating systems. For example, heat pumps are very efficient, but they are difficult to install and operate, so it is advisable to use them for large agricultural complexes. For a home greenhouse in the garden, stove heating may be the best option, although a thermal cable is, of course, more convenient, but also more expensive. Drawing up an estimate for equipment and payment for work will help you make the best choice.

The main mistakes in heating polycarbonate greenhouses

1. The most common mistake when building a greenhouse heating with your own hands is bad planning. You should first study all published projects of such systems and draw up a detailed work schedule indicating the necessary materials. This will allow not to make mistakes leading to heat loss, accidents and destruction of equipment.
2. A typical mistake of “craftsmen”: disregard for installation instructions and technical regulations of the technical means used. It is highly desirable to get advice from a specialist on a project drawn up on your own. Better yet, give him the job. The costs will be paid off by competent calculations of thermal installations, scope of work and the choice of reliable equipment.

Popular questions and answers

Answers the most common questions from readers Maxim Sokolov, expert of the online hypermarket “VseInstrumenty.ru”