Hello. New guy here so bare with me on this question. I am a do-it-yourselfer looking to add a 4-ft hot water baseboard to our unheated mudroom. The mudroom is about 5x15. A 15-ft wall (with door) separates the mudroom and living room. On the opposite side of the wall (living room side) is a baseboard. Basically the living room has its own loop. So it comes up through the floor, along this wall, turns 90 goes down another wall, then loops back the same route and then down through the floor. Ok..so here's the question:

Can I place a tee on the supply line going into the existing baseboard, go through the wall, and then tie into the new 4-ft baseboard for the mudroom on the opposite side of this wall? Then can I just cap this line at the end of the baseboard? or do I have to make a loop?

Hopefully someone can shed some light on this. Thanks in advance for any help.