We will be installing a new mid-efficiency furnace and air-conditioner. We are told that we will need a chimney liner. The old furnace is still using the chimney, but the new furnace will have a vent going out to the side of the house and the only appliance that will still utilize the old chimney will be the water heater. So what's the point in installing a liner? Are we getting charged for something that doesn't need to be done?

Thanks