Understanding the Differences is Important.
When designing a condensing boiler or water heater system, one important consideration is what material should be used to vent the appliance. For some appliances, the Manufacture will only allow AL29-4C grade of stainless steel. But some Manufactures will also allow PVC and CPVC, under strict guidelines.
Let’s look at some questions and answers addressing Stainless Steel vs. PVC/CPVC
Selkirk Flue Systems
Heat Fab Condensing Flue Systems