Keeping and providing heat inside a greenhouse is highly dependent upon geographic location, where the greenhouse is sited, whether or not you have a dwarf wall and when you need to heat it.
There are a number of actions you can take to retain heat in the greenhouse.
Cold at ground level can bring down the temperature of a greenhouse over the winter months. Providing some sort of protection to the lower panes around the greenhouse can help to counter this effect. Some manufacturers provide detachable wooden boards, other options include having a dwarf wall. Inside the greenhouse it is common practice to line the glass with bubble wrap, attaching sheets of the material across the glazing bars. This effectively acts as double glazing and holds heat both between the glass and the plastic sheet and within each of the bubbles in the sheet. The disadvantage of this approach is the possibility of condensation and the reduction of sunlight.
To provide additional heating the choice is quite wide. Electric, gas, paraffin and hot water heating systems are all in use. Each has its pros and cons. We supply electrical, gas and paraffin heating systems as well as rolls of bubblewrap.
When planning your greenhouse consider what you intend to do with it and whether an internal partition may be useful, so that you can have both heated and unheated areas in the building.
If you have any doubts don't hesitate to ask us for advice.