[NeedSpace]

I recently I purchased a rental property. The house is about 140 years old. One of units I pay the electrical bill because the basement is on it and it has the washer and dryer.

The previous owner told me the bill varied about $150-200 a month. my first bill was $580. I figured, maybe startup charges (which turned out to be untrue) caused the big cost. In Aug I didn't get a bill. So I didn't worry. Today I logged into my account and found a bill for a whopping $1600! This is a 1 bedroom unit. This is about what I have paid for my electric in my own house for the year. There is no electrical equipment I can imagine would cause this. I have owned 4 other houses in my day so not my first rodeo.

Called electric company, they said they sent a driver to my house and physically checked the meter. They also confirmed about $150-200 electric bills to prior owner.

Water heater is gas, furnace is gas, ac is a window unit but not that old. Tenant has a computer and a tv but really nothing else. Basement has a few lights, no sump pump or anything like that. Water is town water (no pumps). Frig is 1 year old. No dishwasher. Just a washer and dryer. Tenant is responsible and turns off AC when out of the house. Plus he was away for about half the month.

I am having the electric company come out and check the meter to make sure it is working properly but do you guys have an ideas on:

1) what could be causing this?
2) How to diagnose what is causing this?
3) How to fix the situation?

Thanks in advance.