Hot water is generally what really pushes up gas bills, how many people will be taking showers? how much laundry, dishwashing? I have seen one tenants bills be 200% more than another for the same amount of space in the same building. Calling National Grid to see how much the prior occupants use was, does not help if you do not know more about how they lived in the space.
Realty on the Greene, LLC
Good luck and I hope this helps!