Does my chimney need a new liner?

[Jimmy]

When selling my home, the home inspector recommended the chimney - which we have used for years - get a new liner just for the water heater.

This will cost several hundred dollars that I can't really afford. Is this necessary?

The water heater works just fine the way it is.

[home improvement guy]

I have seen several installations where the water heater and the furnace would share a metal flue pipe that would then vent to an older clay chimney lined with clay tiles. The exhaust gases from the two units would often be warm enough to draft to the outside through the colder clay flue pipe.

When a new high-efficiency furnace is installed, it will be vented through a PVC (polyvinyl chloride) plastic pipe through a sidewall and the water heater will be orphaned to vent by itself. The gases from a water heater are not hot enough to vent through a cold chimney and will spill out of the draft hood on the water heater. If this happens too often and the water heater is in a restricted area or small room, the spilled gases can produce carbon monoxide.

Carbon monoxide can be fatal in higher concentrations. By adding a flue liner to the chimney, the flue gases will remain warm and will rise to disperse to the outside environment. All flues and appliance venting installations should be performed by a qualified HVAC technician who understands ventilation.

Other contractors may not understand proper ventilation techniques. A flue pipe must have a positive rise starting at the appliance and extending upward to the main chimney connector. If there is a dip in the flue pipe or if, at any point, it turns downward, the appliance will not vent properly and can produce carbon monoxide contamination.