Built an addition and added radiant heat in basement - looking for recommendations\approaches to heat this space.

Old space heated by a Weil-McLain HE-6 boiler (Input BTU 167K/Output 137K). Approximately 18 yrs old. 4 zones with 154 feet of baseboard. Sq ft of original space (sans basement = 2,767 sq ft). Old space is 2x4 construction R13 walls. I also have a AMTROL\Boilermate indirect water heater.

Added radiant tube to basement (in slab for addition and slab on slab for old space). I have 1,200 linear ft of 1/2" PEX in slab\slab on slab. 600 linear ft of 1/2" PEX staple up for kitchen tile floor and 600 linear ft of 7/8 PEX in slab to heat garage. I've been told that this totals to something around 77K BTU required for heating. All of this tubing lacks Oxygen barrier. Basement is approx. 2,621 sq ft.

The new addition is heated by force air via coils (both of which have a capacity of 45k BTU). New space is 2x6 with closed cell foam (R7/inch) insulation. R25/walls and R40/attic. New area is approx. 2,000 sq ft.


I did Heat Loss calc with the Slant Fin Hydronic program and total Heat loss (BTU/HR) is about 96,998.

My questions are:
- Do you recommend that I keep the radiant heat on a separate system? Would you recommend tankless (e.g., Takagi or Munchkin) for this application?

- Should I replace the old boiler and size a new unit for both the baseboard and force air? My assumption is that as a side benefit I could go with a modulating type that would help during non-Winter months for hot water.

- Should I leave the old unit and add a new unit for both the radiant and forced air?

Thanks for your help.