A greenhouse needs to have sunlight in order to get nutrients to the plant that is needed. There are certain times of the year when the size of the greenhouse means that it is hard for the plants to get the nourishment it needs from the sun. Supplemental heat is needed in all sizes of greenhouse during certain times of the day when the weather is a little cooler outside of those walls.
Some of the more common forms of heat and energy in the greenhouse are coal, oil and gas. It is going to depend on how large your greenhouse is and what the size of the budget is to determine what type of heat you pick. Electric is another form of heat only it is one that is used as a back up as it can be more expensive than others.
There are all different types of heat that can be used in your greenhouse and you can use different sized equipment. Large commercial greenhouses may use gas hot water heated coils through the greenhouse and there are smaller hobby greenhouses that may have a gas powered standing heaters. There are matching preferences and the needs will be met when you are heating the greenhouse.
It makes no difference what type of heat you decide to use. If you want to distribute the energy through the greenhouse, you simply need to choose the best one for your needs. Fans, tubing and sometimes gravity are what will get the heat from new end to the other of the greenhouse.
Remember you should choose an open burning flame of any type in the greenhouse that you would have to be careful of the gasses that are given off by the heat so that your plants are not lacking the proper air requirements for good growth.
The arrangement of tubing through the greenhouse for hot water can be very costly to set up, but in the end, it is going to be very efficient for you a will last for years to come.
In commercial sized greenhouses were boilers and heating systems are installed, you will need to put them in as you would a home and this can be costly. When you have your seeds planted and your heating system fails, or the electricity goes out, you need to have some kind of back up idea. A back up generator or back up heating system with a warning system is a good idea so that you can get your heating system back up running in no time at all.