My husband and I have a two-family house in Boston built in 1902. Bought it in 2001, live on the second floor, and have had two long-term tenants on the the first floor. There are two oil burners in the basement, and the heat is forced hot water radiator heat in both units.

Here's the thing. The first floor stays at 65 with less than half the amount of oil required for the second floor to stay at 65. I bleed all the radiators every year, and have had the burners cleaned every year. There's no real difference in the number of windows/doors in each unit. We have an attic above us; tenants have a basement below them.

Why do we use three tanks full of oil for every one they use downstairs when our thermostats are set at the same temperature? Must this be an insulation issue, or could the pipes somehow be distributing our heat to their radiators?