2-family: How do I account for some shared electrical

[Ben Morris]

I am in the inspection period for a 2-family where the owner lived on the lower level and rented the upper.  The electrical is split per unit but there is a single furnace and hot water heater for the entire house.  The lower unit controls the furnace, and thus the electricity required to run the furnace blower gets billed to the lower unit.  This works fine when the landlord lives in the lower unit, but I am planning on renting it out.

I am fine with covering heat and water which is pretty common in my area, but I am having difficulty coming up with a way would be to account for the electricity required to run the furnace.

Here are the average utilities for the last 24 mos:

• Lower electric - 86 Paid by tenant, but includes some electrical for whole house
• Upper electric - 45.  Paid by tenant
• Gas - 60 (hot water + furnace)  Paid by landlord