New Tankless Water Heater

I need a new water heater and I am thinking about a tankless unit.What I want to know is can I vent it through the existing vent from my old water heater or do I have to run a new vent.

Tank-less heaters need a 4" vent. Most tank type heaters are 3". Plus you may need a larger gas line. Tank-less are 3/4" and tank type are 1/2".

John

A tankless water heater is much more efficient which means more moisture in the exhaust. You "can not" use the old chimney.

You will need either a new plastic or a new stainless. Most are being done with plastic.
The old galvanized steel won't cut it.