Why is a greenhouse heater useful and which variants are available?

Overwintering and year-round growth possible

Whether used privately or commercially, the purpose of a greenhouse is to ensure year-round growth of the crops it houses. It doesn't matter whether vegetables, herbs or fruit are grown. But especially in the cold months, there is a lack of the necessary warmth and sufficient light to ensure healthy plant growth.

An additional use of the greenhouse is the safe overwintering of valuable ornamental plants. Year after year, beloved flowers, shrubs, perennials and ornamental trees, such as dwarf fruit or olive trees, find their way into the greenhouse to be protected from frost and snow.

What temperature should be achieved?

There are three main types of greenhouses:

•    Unheated greenhouse
•    Temperate greenhouse
•    Warmhouse

In a unheated greenhouse, the purpose is only to ensure that a temperature above the frost line is reached. A temperature-controlled greenhouse, on the other hand, is heated all year round to a minimum temperature of approx. 10-18°C. If temperatures are consistently above the 20°C limit, it is called a greenhouse.

The heat requirement of the greenhouse depends on the desired indoor temperature. The energy required to heat the greenhouse depends on three basic factors:

• Insulation of the building envelope
• Size of the glass surfaces
• Difference between outside and inside temperature

This results in the following formula for calculating the heat requirement:

Energy requirement (watts) = k-value of the insulation * glass area in m² * difference between outside and inside temperature (°C)

Choosing the right heat source 

Frost monitor

Frost monitors are usually simple paraffin heaters that are only intended to protect against frost. Although they are relatively inexpensive to purchase and operate, their range of applications is limited. The frost guards must be ignited manually and cannot be automated via a timer. In addition, precise temperature control is not possible. 

Gas heating / gas cannon

Gas cannons have long been popular heating sources for greenhouses, as they are inexpensive to purchase and operate. However, as air is used as the heat transfer medium, the systems are less efficient. In addition, the operation of fans is often necessary to avoid stratification of the air. Manual ignition, regular checking of the gas cylinders and limited temperature control are among the limitations of such solutions.   

Solar heating

A distinction is made between solar thermal and photovoltaic solar heating systems. With solar thermal energy, (rain) water is heated in collectors and released again via convection heaters. With photovoltaics, the energy generated is stored in batteries and can later be released via electric heaters. Although the operating costs of these solutions are low, the initial costs are very high. In addition, a lot of space is required as they cannot usually be installed on the roof of the greenhouse, as this would obstruct the sunlight reaching the plants.

Electric infrared dark heaters 

Infrared dark heaters, which are inexpensive to purchase and quick to install, are an ideal solution. The infrared radiation generated has a similar effect to solar radiation, which primarily heats the plants and the soil, but not the air. Thermostats allow precise time and temperature control so that a plant-friendly climate can be realised, even with different zones if required.

All the advantages of electric infrared radiant heaters at a glance

• Quick and space-saving installation, can also be used as a mobile unit if required
   
• The infrared radiation heats the plants and the ground directly 
   
• Low heat loss as air is not used as a heat transfer medium (even with poor insulation)
   
• The leaf temperature is higher than the air temperature, minimising the risk of falling below the dew point (mould formation)
   
• Lower risk of insect infestation and fungal growth due to reduced air humidity
   
• No draughts as there is no need to use fans to circulate the air
   
• Plant-friendly climate with different zones possible
   
• Efficient and precise time and temperature control via thermostats 
   
• No maintenance required, e.g. for topping up fuels
   
• Co2 neutral when operated with green electricity