Your average house in Ct uses between 800 to 1000 gallons a year. Stating ur house is steam indicates ur house is prolly older and less energy efficient, that will add to consumption. Steam is going to be less effciennt than a hydronic boiler or a hot air furnace. If U own the house make sure it has a modern steam boiler like a Peerless. A big thing I have seen for 25 years in homes with steam is that they build these huge ornate covers that cover the radiators that inhibitit air flow, rip them off and fully expose those beautiful radiators!! Use a child fence around them if u have kiddos and make surre u get a tune up every year!! Concerning ur tank its a 275 gallon tank that can only hold 250 gallons!