3 questions about cooker hood extraction rates
Isn’t the main purpose of a cooker hood extracting smells and grease from the kitchen? The extraction rate of the hood indicates how effectively this can be done.
The extraction rate can also be called airflow. It refers to the amount of air (in m3) that can be extracted in one hour. The higher the extraction rate, the more air can be removed.
Here we answer three key questions on extraction rates.
1. Is the extraction rate the same for recirculating and ducted hoods?
If a hood is used in recirculation mode, then the air is forced through a charcoal filter. This will reduce the airflow by up to 30%.
If a hood is ducted out, then the extraction rate will be affected by the length and diameter of the ducting run and the number of bends. The more bends and the longer and narrower the ducting run, the lower the extraction rate. You may notice a reduction in efficiency if the ducting run exceeds 3-4 metres and has more than 2 bends. Most manufacturers recommend rigid 150mm diameter ducting for optimum results.
2. What extraction rate do I need?
To calculate the appropriate airflow level for your kitchen, you should multiply the volume of your kitchen by 10.
For example: If your kitchen is 3 metres wide, 5 metres long and 2.7 metres high, your calculation will be:
(3 x 5 x 2.7) x 10 = 405
This means that a hood with an extraction rate of 400 m3/h should achieve efficient ventilation of the room.
3. How is the extraction rate reported?
Most manufacturers, including BEST, comply with the European standard IEC EN 61591. This means that the airflow is measured in a realistic scenario: after one meter of ducting plus one 90° bend plus one more meter of ducting.
If a hood can only be used in recirculation mode, then the airflow should be measured at the point of the metal grease filter with the charcoal filter in place (which reduces the airflow). This lower airflow figure is reported for BEST recirculation-only hoods. Not all cooker hood brands use this accurate reporting method.