Cost is a consideration. Centralized systems are more expensive to install than are laocalized ones. Type of fuel may be a considration. Coal and low grade oil can not easily be burned in localized systems. Type of crop and need for soil heat may be a consideration.
Centralized systems are often steam or hot water while localized systems are often hot air.
Maintenaince may be an issue. With a central system 1 or 2 large boilers will have to be maintained, while with a localized system many small burners may have to be maintained. In order to compare fuels, cost comparisons must be based on equal energy content for example 100,000 BTUs. Once the cost per 100,000 BTU has been calculated so the the least expensive fuel can be selected, then it might be useful to begin to calculate the cost to heat a greenhouse. Through a series of calcuations that will be discussed later, it can be determined that the greenhouse in question will require 200,000 BTU per hour to maintain temperture.