Water heater options
We just moved into a 7000 sq foot (3000 main floor), 15 year old house. It has two 50 gallon power vent gas water heaters on each side of the house. One of the water heaters gave up couple days ago. The other one supplies a guest bath and an extra bathroom in the basement that we don't plan on using. What are our options as far as replacing the water heater. We are family of four and don't take showers simultaneously. In our old house we had a 50 gallon water heater and never felt we ever ran out of water.
1) Should we just replace the main water heater that is broken with a similar one?
2) Replace both the water heaters with one 50 gallon since we don't use the other water heater and it is already 15 years old?
3) Go for a solar water heater?
We are also considering going for geothermal/heat pump when the need for replacing ac/furnace comes up in future. Keeping that in mind, any specifications to get the kind of water heater? Thanks.