I can't tell you what is cods or not, don't know what a Tarion warranty is, but you smell cooking odors in the basement because you get fumes and grease drawn downward and will tend to settle along the way. You are right --t eh fan has to try to overcome the natural rising nature of fumes, steam, anything heated. You could also have a buildup of grease, dust or other muck in that line. It will continue to get worse. Has it ever been cleaned out? At some point, that can become a fire hazard. I would have it looked at, and if it were me, I'd get it changed, whether it was on my nickel or someone else's. It is not going to get better.

Thanks for the reply. A Tarion warranty is a new house warranty that lasts 2 years against house defects and up to 7 years on other defects like foundation issues. I looked at the warranty and couldn't find anything about venting the range hood so I don't think this is covered, especially since there are some vents on ranges that are specifically made as down drafts. I'm not sure we can change the configuration the way the kitchen is laid out. The wall in the kitchen that the stove is on is only a partial wall and doesn't go all the way up to the vaulted ceiling. I appreciate your response.