On 2005-10-06, Wayne Whitney wrote:

If so, why doesn't anyone make a condensing tankless gas water
heater?

To followup up on myself, apparently there is at least one condensing
tankless gas water heater, the Takagi T-H1. Unfortunately, it seems
to cost 2.5 times as much as a comparably sized non-condensing unit.
That's a big price increased to go from a 0.85 Energy Factor to a 0.94
Energy Factor. I'm also surprised that it still requires a Category
III (sealed stainless steel) vent.

Cheers, Wayne