Improving the efficiency of heating water with a holding tank?

Question

How does adding a small (40 gallon), efficient holding tank (like a Maraathon or Stiebel Eltron) along side my exisitng system improve the efficiency of heating domestic hot water (I use heating oil to heat my water)?

It makes no sense to me, because my boiler keeps water in the water jacket and the additonal water is just more heating load... or maybe I'm confused about how my boiler really works???

Answer 1

You said it - it makes no sense.  The coil in your oil-fired hot water boiler has a better "recovery" rate than any seperate hot water heater and any other type of fuel.  And, the more water you have to "keep" hot, the more fuel you consume on "stand-by".  All this would do is provide additional back-up reserve that you'll probably never need.  If you don't have a current problem with hot water supply running short, don't mess with it.  To me, people who put out these kinds of ideas are just out to sell another gimmick.