WARNING! We are coming across a lot of the ABS venting on power-vented water heaters that is cracked. If you have a water heater with ABS coming off the top, please take the time to inspect for visible cracks in the first 90 or 45 degree fitting. That pipe is responsible for exhausting harmful fumes outside and if it has a crack itwill allow those deadly off-gases (Carbon Monoxide) into your home. The have changed the code so that new furnaces and water heaters require a specific PVC venting material that is resistant to temperature fluctuations, however the old ABS is allowed to remain on older units until the unit is replaced or the ABS requires repair. At that point the entire venting system requires the upgrade to PVC.