tankless w/air handler

rheemball

Rheem has come out with a condensing tankless unit as well as an air

handler with hydronic coil.  put together we have a modulating home

heating application as well as domestic water.  I am thinking of leaving

my 40 gallon water heater as a holding tank only to raise water temp

from the street to room temp...this tank will not be used to heat the water at all. 

then throw the return water from the hyd a.h into the 40 gallon tank to

raise that water temp even more.  my goal is to lower the temp rise at my tankless for better efficiencies!!    the tankless unit is designed to periodically cycle the pump to prevent stagnant water from sitting in air handler.  any comments on this application?  should I be worried about the condition of water sitting in my tank at such a low temp potentially?

Ironman

Yes, You Should Be Concerned!

Doing what you're proposing will make a giant Legionella breeding machine!



And returning warm water to a tankless will make it less efficient, not more. It will also decrease your warranty.