Convert heat to electric or hot water to gas?

[John A.]

Here's the situation: I've got a single story SFH in southern AZ. The house has natural gas lines running to the gas furnace, the kitchen and the laundry room. The only thing hooked up to the gas line is the furnace. Currently, the stove, clothes dryer and water heater are all electric. The water heater is in the laundry room. There is no roof vent in the laundry room.

Now my question:  The tenants always complain they have to pay $20 a month in the summer for gas service they aren't using.  Both the furnace and the water heater are getting up in age.  Given this situation, would you convert the house to 100% electric or convert the water heater (and maybe the stove) to gas?  Or are there other options?