I had a Munchkin boiler installed a couple years ago with 3 zone valves. Only one of the zones was initially connected -- to baseboards on my main floor. The other 2 zones were intended for a future 2nd floor addition and finished basement.

I've now had the 2nd floor addition framed (plumbing and wiring finished, insulation next) so want to heat it now. I'll have access to the 2nd story subfloor (from below) and would like to install radiant tracks and tubing to the underside of the subfloor to heat the 2nd floor (instead of installing baseboards). I plan to convert the main floor zone from baseboards to in-floor as well.

My main question is: can I use one continuous loop (1/2" tubing?) for the 2nd floor zone? Or do I need to split up that loop into 2 or more sub loops? If the latter, is it as simple as adding wyes/tees to the start and end of the zone loop? (I'm concerned whether that will ensure even heat flow through the sub loops?) The second floor is approximately 800 sq feet and consists of 3 bedrooms and one bath.

I am aware that I will also need to reduce the boiler temp for the conversion from baseboard to radiant.

Anything else I need to know or other recommendations for this conversion?