furnace venting

Yesterday the HVAC company we've been dealing with sent some people over to clean the vents. While I was there I spoke with them, one of them suggested that I needed more cold air return vents for our house (we have 1 now) or we'd void the warrantee.

Later on, I called the heating representative from the HVAC company we've been dealing with just to see what was going on and he said that they didn't know what they were talking about. Essentially he said our furnace was multi stage and would shut off before anything bad would happen to it. Also that it was extremely unlikely in his long professional experience that we'd need another vent.

If it's the case that we can't really harm the furnace we'll take his advice and just let it go and see how well it heats the house