Just had new Modern-aire ps10-10 installed. When the Hvac person was doing the ducting ( which is a short run to the wall), he noticed there was not a backdraft damper and said all the hoods he has ever done the venting for come with one.. I called both my sales person from retail place of purchase and Modern-aire. This model does not come with one and they said I could order one to be installed but not needed? My hvac person would have to undo ducting to put it in. He was aware of this when he finished the project. Do I really need one? I live iin California and don't get real cold weather. Not sure?