Also, the furnace is less than one year old, but the hot water heater is pretty old.

Is this an oil fired furnace? Is the hot water heater oil fired or electric?

Do you have a powered exhaust fan in your attic?

Yes, everything is oil. There is no fan in the attic, and the house is 20 years old, so I don't think it's an issue of any exhaust fan creating a vacuum in a very tight home.

"exhaust smell entering the home when the furnace fired up and the blowers blew warm air into the home"

I would investigate to see if you have a cracked heat exchanger. You may also have a combustion and/or venting issue with the furnace or hot water heater.

Did the furnace tech smell the odor? Maybe you need to call in a new service company.

The furnace tech did smell the odor, and simply blamed it on the chimney. He actually made a comment that the smell was so strong that even someone like him, who is used to the smell, thought it was strong. It might be time to call another furnace company, but the furnace is under warranty with our current service provider. Maybe that is one of the reasons that they continue to tell us nothing is wrong...

Is this a brick chimney? Maybe there is a problem with chimney itself or how the venting was installed. Get an inspection by an independent chimney specialist. You need to get this resolved ASAP.

The chimney is brick, on the exterior of the home. I've read a lot about that not being an ideal system, but it's what we have. The furnace tech is currently in the basement for the 3rd time, and is talking about installing an exhaust fan on the exhaust pipe before it hits the chimney to help push the exhaust out. He says the draft is "crap." He also mentioned that the newer furnaces (which this is) don't produce enough heat to induce a strong draft, which I have heard about as well.

We did have the chimney inspected - twice. And both inspectors said that it's fine. This is why the problem has been so frustrating. Everyone is telling us everything is fine, and it clearly isn't.

Should we try the fan?

What is the rated efficiency of this furnace? The higher the efficiency, the cooler the exhaust gases. A cool exhaust has more difficulty rising up the chimney. There is some truth about the what the tech is stating.

I am not an expert, but I don't think an exhaust fan is the correct solution. You need to install a stainless steel chimney liner in order to solve your problem.

Thanks for the input. I think we'll get some quotes for a liner...

i know this was a long time ago, but I am very curious was the resolution to this? We are experiencing the exact same issue!