[stevehull]

I use a dual tank set-up- and it works great! The first tank is preheated by the superheater in my geothermal heat pump. In the summer, this provides about 80-100% of our hot water needs. I used to have my drain back solar system plumbed into it, but I get a lot more efficiency from the GT heat pump by cooling off the desuperheater.

This tank is just a 50 gallon standard dual element hot water tank. It was a "dent" special from Lowes for $50.

The output of that first preconditioning tank then goes to a tankless water heater for a small boost (if needed).

My ground water temp is about 60F and I need 110F water - delta t of ~ 50 degrees F. In the summer, the temp is often 100-105F (or higher) in this preconditioned tank, so I save some 80-90% on water heating costs.


I do have the electric resistance elements hooked up in the preconditioning tank for back-up, but I have literally never turned them on. This tank is wrapped in fiberglass, then scrap bubble wrap and finally some re purposed laminate fashioned into a cylinder (additional R40) surrounding the extra insulation. Put it on a safety pan with a drain hose and it just sits there and has for years.

At installation, I did put in a bypass (with unions) for the tankless so that if I need to remove the tankless for service/replacement, then I still have hot water.

Very basic, inexpensive and it works well. I can't understand why a air source geothermal hot water tank then feeding into a tankless would not offer similar attributes.

Steve