Why? What is your heating load?

You don't need 2 different systems, you just can't use your Domestic Hot Water as the 'heating agent'.

You can use your boiler to heat both your house and your DHW, you just need to use a Heat Exchanger in your hot water storage tank. You won't be drinking or showering in the same water that is flowing through your floor.

I don't like it. Seems to me that if you have a heat source capable of warming a house of this size; an indirect coupled with a mod/con would be much more efficient. Unless the DHW needs (in many cases) exceeds the heat loss of the house. JMHO