Just bumping this thread since we are finally in the midst of making a decision on a water heating system.
Two options:
Keep the present water heater and add an additional storage tank with a recirculation pump between the two (50 gallon plus another 80 gallon for a total of 130 gallons BUT have two tubs which together when full consume 80 alone).
or
Go with a hybrid tankless design.
http://www.hotwater.com/water-heaters/residential/hybrid/next-hybrid-gas/Pluses and minuses:
Extra storage tank means reduced storage space and would not have unlimited hot water (estimating that the extra volume would be enough is still an uncertainty). Cheaper installation and can keep present venting (steel pipes connecting to and out the furnace chimney).
Hybrid means smaller footprint, high efficiency, endless hot water and based on the design, no cold water sandwiches (our main issue with the standard tankless system).
However, new ventilation is required (cpvc piping and not out the furnace flue) which means higher installation costs.
Potential for higher maintenance (the tech is still a bit new and we've heard downsides to the required annual flushing of a tankless setup as previously mentioned). At least the AO Smith unit has a 6 year warranty for tank AND parts which provides a bit of confidence in the product.
Just waiting to hear on prices for these options which could also be a deal breaker.
If the extra tank idea comes in around 2k but the hybrid option is say 8k, the choice is easy.
