I bought a o smith water heater at a builders auction. The spec sheet on the unit says natural gas. The auction says it is propane. Is there an easy way to find out which it truly is?

Look at the gas valve, it should say. If it has been changed by someone and not marked, you will need to measure orifice and manifold pressure.

Changing a gas water heater from natural gas to Propane is a easy job. You simply swap one orifice for another. Purchase the orifice you need and change it out. Good luck, Tom

Changing a gas water heater from natural gas to Propane is a easy job. You simply swap one orifice for another. Purchase the orifice you need and change it out. Good luck, Tom

How about pressure regulation?