[QUOTE=Jack2007;2062244]There IS a barometric damper.
Then why did the contractor who sealed the ducts suggest you to look into having a barometric damper vented to ????? the outside?
some questions for you :
What type of heating was installed before you went to an oil furnace?
Did the same chimney take all the fumes out then?
Has the chimney been altered recently or re-routed ?
Have you tried adding a few feet more in heigth to it?
Is a proper (down draft preventer) cap installed ?
Knowing the answers to these above questions will help us make proper suggestions on how to eliminate your problem.