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simple ventilation to allow 15 Litres a second airflow into three bedrooms

2 houses next to each other need airflow from fresh air feeding into three bedrooms for one house and two bedrooms for the other house. they need to be quieter than 35dba. Happy for the ducting to go from the bedroom floors with a closable vent and then have ducting to the baseboards of the house (both houses have a bit of room underneath We need to show council specs to show minimum of 15 l per second of airflow into each room and decibel of less than 35