Rhett: Otto gives me a ride to work every morning and expects me to help pay for fuel. But I shouldn' t have to pay. Giving me a ride doesn' t increase the amount he spends on fuel, since he has to go right by my house anyway. Barbara: By that flawed logic, you would be entitled to the warm air that heats the unused spare room of my house, if you could divert it to your house without increasing my expenses.
The dialogue provides the most support for the claim that Rhett and Barbara disagree over whether giving Rhett a ride to work increases Otto's fuel expenses.