Many factors are involved when determining what size of an air conditioner or furnace would have the required power output to cool or heat your home. These factors include the extent of exposure to the sun and the outside air, the thickness and type of outside wall insulation, the size, type and number of windows and outside doors, the ceiling height, etc.
Generally speaking, however, if you live in Southern Ontario, you may use the charts on the link below to estimate the correct size of the heating or cooling product that you may need for your home:
Keep in mind that the following furnace output power estimates are aside from the furnace's nominal power ratings. For example, a 95% rated efficiency furance with a power rating of 80,000 BTU/hr has a power output of 0.95 x 80,000 BTU/hr = 76,000 BTU/hr.