Steam Baseboard vs. Steam Radiator

I am assuming you own the building and can make these changes, but depending on the amount of money you want to spend:

• Turn down the temperature on the thermostat
• Move the thermostat to one of the apartments, probably in a locked box so the tenants can't actually control it, but it at least reflects the real temperature. You can also get thermostats with remote temperature sensors, in which case you could install the sensor in the apartment
• Install a radiator in the common area, so it at least somewhat reflects the temperature of the apartments
• Install a multi-zone system, with a thermostat in each apartment and independent solenoids that control heat to each apartment. This is obviously the most invasive and costly option, but would put individual control to each apartment and possibly reduce your overall heating costs. Using programmable thermostats would also help, as it could lower the temperature at night and possibly during the day while no one is home. The only problem with this is you can probably only do it with individual tenant control, and if the tenant is not paying for the heating costs they don't really have any incentive to lower the temp at any point (unless they like it colder at night).

Try this on for size:

Annual Oil Bill * Efficiency = Cost of Oil actually used for heating. (The rest is waste).

So on an annual bill of $1000, you are currently paying $650 for heat, and $350 out the chimney. (i.e. $650 is as low as you can go with a 100% furnace)

So, if you were to replace that with an 87.2% furnace, your annual cost would be $650/87.1% = $747, and there is about $100 waste. (Note! this is a savings of $250 per $1000 of Oil)

On the 86.1%, that's $650/86.1% = $755 for a difference of $8 per thousand of oil currently used. At that rate, the new furnace would take 375 * (time in which you use $1000 of oil) to pay off the difference.

This analysis is based purely on BTUs produced at the burner.

Now, there are other factors, such as air flow and distribution which may significantly affect your oil use, and the bigger furnace may be more efficient in other ways.