Isolating a condensing boiler

[mustangfan]

My plans are to run a condensing boiler to heat my radiant floors for the house. I have 4 loops at 200 feet long for the kitchen and another 4 loops at 200 feet for the bedroom and bathroom.
I have a 40 gallon hot water heater that I want to use for a storage/buffer unit and I will fee that from my outdoor boiler most of the time.
I will have a primary loop around the hot water heater that will include a heat exchanger so I can use the condensing boiler to heat the water in the buffer tank, when not using the outdoor boiler. I will feed the floor on secondary loops via a mixing valve to get the water temp to the correct setting for the floor.
My question is can I run the condensing boiler thru the heat exchanger and then back to the boiler? Will this be enough of a temperature drop for the boiler?

 

[Vtor]

Many are setup like that when you need to separate potable or not-oxygen free water from the condensing boiler. Circulator on boiler side and of course, circulator for the radiant.