condensing hot water heater...

I have a desire to learn more about "commercial" hot water heaters that have the heat evenly distributed within the water, as opposed to just heating the bottom like in a conventional hot water heater.
AO Smith makes the Cyclone and Vertex. A company called Phoenix (I think) makes one that is stainless and therefore requires no anode rod (is that true?).
Are there a bunch of companies that offer these products? Is there a national wholesaler to turn to?
I'll go thru the Craigs Lists again, too. Just looking for a bargain.
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