The unit of measurement for sizing kitchen fans is CFM - how many cubic feet per minute they are able to move. While the Ontario Building Code does require that there be mechanical ventilation in the kitchen, it does not specify the minimum rating. However, in section 18.104.22.168.2 it defers to another, internationally recognized regulation - ANSI/ASHRAE 62.1 - Ventilation for Acceptable Indoor Air Quality - which is to be used in all cases to define the minimum air flow required. Accordingly, the required minimum kitchen fan size is 100cfm.
But what size fan is needed to be truly effective? The kitchen fan certification authority - the Home Ventilation Institute (HVI) - provides guidelines that factor in four elements through a complicated formula to arrive at a minimum CFM rating - 1) area of cooking surface, 2) amount of heat generated by the stove, 3) volume of the room, and 4) air-flow resistance in the ducting.
If we were to follow their guidelines to the letter - and home builders generally do not - then everyone would have an extremely powerful unit in the $500 to $1500-plus range.
Most Ottawa homeowners want a much simpler range hood solution, so we have developed a more straightforward formula that combines the two most critical HVI elements - room size and heat source - to select units that both meet the Ontario Building Code and the actual requirements for normal, every day usage.
range hood is rated at 200 to 250cfm. A Level-2
unit is rated at 250 to 350cfm. A Level-3
unit is rated at 350 to 450cfm. A Level-4
unit is rated above 450cfm.
If your kitchen is small and is a closed room rather than open-concept, and your stove is electric, then a properly installed Level-1 range hood connected to the appropriately-sized exhaust ducting will meet your normal needs. If your stove uses gas, then a Level-2 range hood is more appropriate because gas generates more heat.
If your kitchen is mid-sized or small but open to the rest of the house, and your stove is electric, then a properly installed Level-2 range hood will meet your normal needs. If your stove uses gas, then a Level-3 range hood is needed.
If your kitchen is large or mid-sized but open to the rest of the house, and your stove is electric, then a properly installed Level-3 range hood will be adequate. If your stove uses gas, then a Level-4 range hood is prudent.
A still larger kichen should have as a minimum a Level-4 range hood.