I have an outdoor boiler running into my house. I also have a 135 litre tank that I want to use to transfer heat to copper tubing that I can wrap around the tank and hook up to the hot water tank. My question is " do I run the 160 degree boiler water through the tank to heat the water in the copper tubing which would pre heat water to the hot water tank OR run the 160degree boiler water through the tubing and the heat the water in the tank?? Hope that makes sense. Thank you in advance for your help!

I would think you would want to use the boiler water to heat the tank, and then run your domestic hot water through the tubing on the outside of that. Is this water constantly circulated or only as needed?

The water through the tubing is on demand, the boiler water is constantly circulating, it would have 100' of 1/2 " copper tubing tightly wrapped around it with heavy duty glass insulation around the whole tank

I am concerned at how quickly, if at all, the hot water in the tubing would cool