Hot Water Loop for Harman SF-250 Into Oil Burner

I would like to use a single wall hot water holding tank and piggyback into oil burner, this way in the summer it would also act as a tempering tank. I spoke with the local Harman service guy, he seemed to think it was a good idea, and should work.
Do you guys think this will work? What psi rated tank do I need, and where can I get one? I have about 63 pounds of pressure coming into the house.
There is a plumbing diagram in the Harman manuel, but it has a hot water heater instead of a single wall holding tank. I want to use this tank to let some of the heat off, and also act as a tempering tank when the stove is not burning. I was reading some posts on here pertaining to this set up,it seems when to much heat builds up the pressure valve opens, letting the hot out and cold in, also is there a difference between a temp. pressure relief valve and a pressure relief valve as shown in the thermo-siphon diagram in the Harman manuel? I have learned a lot from you guys just reading all the posts on here I hope you can help me with this, any input is really appreciated Thank you Craig.