I am closing tomorrow on a property with a fuel oil fired water heater from 1988. The heater is rusted at the bottom and is "on borrowed time" so I am looking to replace it with a natural gas heater. The heater is in the basement next to 2 forced air natural gas furnaces and should be easy to install a new gas water heater however the current tenants in this duplex split the cost of the fuel oil. The gas and electric are separated but if I put a new heater in, I would have to put it on one of the tenants gas meters. Is there something I am overlooking? This property has only 1 water heater and 1 water meter so I pay the water.

@Samantha Klein It sounds like you are not overlooking anything. 

Are the water lines to each unit clearly marked? If so, maybe it makes sense to put in 2 Hot Water tanks and split out that utility as well. 

@Jim Murray I'll have to talk to the plumber about that. If we can't easily add another one, what would you do?

2 water heaters. one for each

If the tenants presently split the cost of the oil why would you ever change the hot water to gas. There seem to be no upside in complicating the situation since there is absolutely no benefit to you.

Buy a new oil fired hot water tank.

@Samantha Klein If you I couldn't easily add another one I would include it. Typically for including hot water we could get between $25-50 per month for rent in my area and the gas for hot water should only cost $25-50 monthly. 

get an electric water heater.

Originally posted by @Thomas S. :

If the tenants presently split the cost of the oil why would you ever change the hot water to gas. There seem to be no upside in complicating the situation since there is absolutely no benefit to you.

Buy a new oil fired hot water tank.

Oil hot water heaters are very expensive and require routine service calls for cleaning 

i think I have a solution . But it depends on the layout of your plumbing . If you can isolate the hot water feeds for both units , put in gas fired instant heat hot water systems