Balanced Ventilation System with heat recovery

I am interested into upgrading my house to a balanced type of ventilation with heat recovery. i have to mention that the house already has installed from when was built (year 2005) a exhaust type ventilation from the two bathrooms and vaskeroom with a small ventilation agregat located under the roof. House is 120 m2 with two bedrooms. If further info or drawings are required, please take contact