Rick Blaine wrote:

Dave in Denver wrote:

So are the new ones just more efficient and need less gas... or do the
new ones have a lower recovery rate? (can not find stats on old
unit... new units have a recovery rate of aprox 40 gph.

Recovery rate and energy efficiency are really unrelated.

Other things being equal, eg wall insulation and heat exchange surface,
a gas water heater with a lower recovery rate, ie a lower heat transfer
rate should be more efficient. Changing to a smaller gas orifice would
likely increase efficiency.

Nick