Any pointers when doing a homerun type system?

You can definitely run ½" PEX to each BB unless the BB longer than 30' which I doubt you have there. PEX A, yes, good. Insulate those runs with insulation that has at least 3/4" wall thickness. Use a good manifold like Roth, Uponor or Rehau that has flow gauges and shutoffs.

Do you want to zone individual rooms? It doesn’t seem like you would have many fin tube emitters in that sized space

A series loop with less than 75 feet of element is within reason. That would make for a lot less concrete cutting. Placing any tubing in the concrete with 3/4" pipe insulation will retain heat in the piping so only the elements are heating the room. If you were to cut channels in each room to a home run location, you might as well just do a radiant floor heat system. (that was a joke). It will be easy to service and purge air from the system with only one series loop. Or perhaps 2 series loops with a common return from the farthest point.

This is a slide that I used to teach Hydronics for the Eastern Heating Cooling Council.

It illustrates that running 120 feet of 3/4" baseboard in a series loop will not work past about 78 feet. So the service call might be not enough heat in the last three rooms on the system but the rest of the house is just fine. This call will happen only on the coldest days of the winter. The milder days will eventually get heat form that poor piping design.

This next slide shows how to fix the problem without a major repiping of the entire system. Take the radiators that are connected to the return and place them on the supply side of the boiler. Increase the common pipe from the boiler to the circulator to 1" and use a 1x3/4x3/4 tee fitting to connect both loops to the supply. Take the mid point of the system so that there are about 60 feet on each loop and run a common 1" return back to the boiler.

I actually did this for a customer that called me up for a price on a new boiler because the old boiler was "too small". Three other contractors bid on the replacement boiler without thinking about the fact that a new boiler with this top illustration's piping arrangement would not solve the problem. For less that 10% of the cost of a new boiler I was able to solve the "too Small" bpoiler preoblem by increasing the pipe size and splitting the series loop into two series loops.

Since you are designing this from the beginning you can design a series loop that will work with no problem. Making a home run system for 7 to 10 radiators is really overkill unless you are placing a thermostat in each room. I do not recommend that! Two series loops maximum on this job is recommended. 3/4" supply and return is all you need for 68 feet of element And if you are operating this from a single boiler for each unit, you will need the smallest boiler you can get. They will all be too big becauseno one makes a boiler that small.

If you are operating one boiler for the entire building and this is just one of the apartment units then you can run 3/4" from the manifold location back to the central boiler room. Just look at this mockup of a 950 sq ft two bedroom layout with 8 baseboard radiator units. there is a lot of cutting needed for the home run system even if you can get a lot of them to a central "shared" trench for a part of the distance from each radiator to the manifold location.

There is a lot less concrete cutting with the series loop design.

Hope this helps.

Mr. Ed

the Viega FostaPex in straight 20’ lengths was good tube for running inside the fin tube enclosure.

The return tube can also run below the fin if you make some hanger wires.

Regular pex or pert in straight lengths will work but needs more supports and expands/ contracts more.

Look for a brand of tube with the outer UV layer