Is this a harebrained idea?

[6t7gto]

I have 2 Raypacks. 500 k and 600k btu.
500 is for floor heat.
600 is for hot water with a 115 gallon storage tank.
I want to take the 600k heat exchanger and place it on top of the 500k heat exchanger.
The 600k HE will be plumbed back into the storage tank with its own set of controls to turn the burner on and off.
And circulating pump.
It will need some sheetmetal work, as the 600k HE is 5 inches longer than the 500k.
I may have to plumb in a mixing valve so the hot water does not get to hot when the floor heat is calling.
Harebrained idea?
thx
david

p.s. Yes I know I could purchase a new heater to do the above but I have all the parts now.
And being retired with too much time on my hands.

 

[MEP001]

Raypak used to have a boiler that worked a lot like that, except the water flowed through the larger heat exchanger before entering the insulated tank. The boiler rotted out because the upper exchanger had colder water going through and constantly rained condensate down on the rest of the unit.