Hi,Thank you for using Just Answer my name is ***** ***** I will help with you question. Please could you let me know the make and model of your extractor.
Is it a new fan?
Sorry for all the questions but it helps get a picture of what is going on.
Is the cooker hood connected to ducting the runs outside?
Is there another extractor fan between the hood and the outside world?Why does the builder think you need a bigger fan?
The re circulation is setup by using filters in the ducting of the cooker hood. What filters do you have installed in the cooker hood. When the fan is turned on and there are no filters in the ducting the fan should extract the air to the outside.If you can see the vents opening that would suggest it is venting outside correctly. Can you feel any suction at the front of the cooker hood.Does the fan speed up when you adjust the speed.