Heating question...I'm paying for heat

[Robert Granara]

I have a 3 family that I pay the heat...it's 3 stories and each floor is it's own apartment...we call them 3 deckers here in Boston...I just bought the house 2 months ago and now it's heat season...looking for suggestions as to which floor I should put the thermostat in...I'm debating on either the 2nd or 1st...I have had conflicting advice by 2 contractors...anyone here have this issue?..to be clear it's FHA oil fired system...thanks