This project involves abandoning a chimney and replacing a Natural Gas HWH. We were going to go solar (with condensing direct vent back up), but after realizing how efficient the new generation HWH are, the savings of going solar are quite small, the payback after incentives AND self install still around 20 years.

Our decision is to just get the most efficient, durable HWH out there and forgo the added expense of solar thermal. We currently have a conventional 50g, 40k BTU with an 89 FHR. Our family of six has been well served by the capacity of this HWH. We currently have no space-heating requirements of the HWH. I'm having a hard time finding a 95% or better efficient HWH in this size and capacity. The best units (listed below) seem to be much larger and often designed for space heating as well. We are not adverse to spending $2-$4k as long as there is real value.

We will be adding a 200 sq. ft. room addition in the next couple years. It's long side faces due south and passive solar heating opportunities abound. Maybe one of these larger WH with side mounted taps would be wise for a radiant slab in the future addition? Is it wise to put radiant in a solar thermal mass? I have seen it done before, locally, but never experienced it.

I have narrowed it down to:
A.O. Smith Next Hybrid (
A.O. Smith Vertex (
Phoenix (
Bradford-Whites Residential Ultra High Efficiency Energy Saver Gas Water Heater (

Does anyone have experience with these units, recommendations of others, or a different strategy to offer?

Many Thanks!