Dual Water Heater question

Does anyone know if there are any codes or requirements or best practices about hooking up two conventionally drafted water heaters in parallel or in series?

Thanks, in advance.

Will, I have seen them both ways, with them separate or combined in series, both for plumbing and vent. I don’t know of any installation requirements that go either way.

No codes or requirements that I know of but regarding best practices I had a water heater added to my system several years ago.

They added it in series with the existing one and the one up stream was the only one that came on whenever water was needed/heated.

I had them switch to a parallel hookup, where the pipe lengths were uniform, and the both came on when water was needed/heated.

Series hook-up is worthless. Parallel (tandem) is the preferred and most efficient method.

You will not find any building codes that address dual-heater installations.

Thanks, Jeff. I agree. Just looking for some back-up.

The only way dual heaters are addressed is how gas or electric is run to them (pipe sizing and load etc.). I agree with Jeff, parallel is the only way to go.