"The most efficient electric heater is the one controlled by a thermostat. Models generate from 1500 - 3000 watts and are usually fan-assisted for a rapid circulation of air. The convector-style heater is merely plugged in and if polythene lining is used for insulating the greenhouse, it will generate sufficient heart to warm quite a large greenhouse most economically. Where tender plants are growing, the thermostat must be set so that should the night frost be severe, there will be sufficient warmth to protect the plants.
"Extremely efficient are the tubular electric heaters which are specifically made for greenhouse use and are available in lengths varying from 2 to 12 feet and may be fixed around the greenhouse so that it will be evenly heated.
"Horticultural electric tubes, also controlled by a thermostat, are most efficient. The tubes are best fixed to the back wall of a leant-to greenhouse or beneath the benches where the greenhouse has a brick or wood base.
"Where electricity is not available, there are several extremely well-made paraffin oil heaters available. They have a slow paraffin consumption and are fumeless if kept clean and the wick is trimmed and are the cheapest of all forms of greenhouse heating."