Consider your climate. If you live in an area that is particularly cold or extremely hot most of the year it will have an effect on greenhouse heating. In a hotter climate you will not have to heat your greenhouse as much. You will have greater greenhouse heating requirements in if you live in a climate that is cold and has a long winter season. Additionally, if you live in an area that often has heavy cloud cover, you will not be able to rely on the sun from greenhouse heating during the daylight hours.

If your greenhouse will be built with a lot of sunlight exposure you may not need to do as much with heating but you will still need to keep the greenhouse heating maintained at the same level if you want the plants to thrive.

Maybe the only area you have to fit a greenhouse is in an area that will face the north and not receive much direct sunlight. You will need to take this into consideration when planning your greenhouse heating equipment.

Remember that trees and tall buildings will also figure into the greenhouse heating equation. If trees or tall structures block the sun for part of the day it can make a difference in greenhouse heating.

It does depend on where you build your greenhouse when it comes to greenhouse heating needs. Some factors you will have little control over, but if you can do anything to improve your greenhouse heating situation, it can save you money down the road.