There are two common ways to heat the greenhouse up. One is hydronic heating way. It heats by boiler and hot water pipes. This type of greenhouse heating system is perfect for cold areas which require heating for long periods in one year. The other one heats up the greenhouse using oil/gas fired air heater. It is widely used in the areas with a short winter.
The main purpose of these two types of greenhouse heating system is to increase the temperature inside the greenhouse in winter so as to create a comfortable environment for plants.