I rephrased your question slightly (please correct me if I’m wrong). I’m assuming this is a condensate tubing from the “A” coil located above the furnace. If so and if that tubing is made out of regular PVC it should not be touching any metal vent pipes because PVC’s maximum service temperature is 140°F. If it is CPVC (you should be able to see that code along the pipe’s sidewall) the temperature is slightly higher: 200°F.
Unless you have some different, high temperature rated plastic hose installed, both of those materials (PVC and CPVC) could start melting if in contact with a hot furnace or water heater vent pipe. It would be wise to re-route the plastic line so it’s not in contact with vent pipes.