Post Reno. heating troubles

[Foz682]

My neighbor has an OWB heating his closed system oil boiler through a plate heat exchanger. The oil boiler never has to fire, simply supplies the house cast iron rads with its circ.
They did a major renovation on the house a few years ago and removed some rads on the main level. Now that level is cool when outdoor temps dip below -15°C. He still has the rads they removed and we're going to put them back in.
Also, the second floor has 4 rads, before the reno they each had a designated supply and return to the boiler headers in the basement. Those all got removed. The guy doing the plumbing decided that the 4 rads could operate in series fed by one 3/4 supply, and returned to the basement by one line.
I checked it out today, supply is 175°-180°, no air in the system that I can tell, first rad it hot, second is warm , others cold and return line in the basement is cold.

He's not overly interested in tearing his house apart again to fix the problem. I'm thinking for the sake of not being too invasive, getting two pipes sent upstairs from the basement between the second and third rad, one to supply the third & fourth rads and the other to return the first 2.
I don't really see any other options, but if anyone has any advice, it would be much appreciated.

 

[Karl_northwind]

That sounds like a reasonable solution. what kind of radiators are they, and are they fed by a dedicated zone circulator or a zone valve with one central circulator? increasing the flow rate may help a bit for this season, so you don't have to shut down for too long, but it certainly sounds like you need more pipes. you can bypass a little of the flow past the first radiator (panel radiators with their shutoffs below them have this built into the connections so you can bypass 1/2 of the flow past the first radiator so the second gets hotter water) which should help if you have good access.

 

[salecker]

Cast iron rads are very efficient at removing the BTU's from the water.
When i was building my house/sytem i needed to get the upstairs rads plumbed so the ceiling could be finished under the loft bedroom.Not having or finding much on CIR's i decided to put 2 10 row rad's on each run of 1/2 pex.
The only time you feel any heat out of the second rad is if the outside temp is below -20C.Otherwise the call for heat is so small that the first rad will remove the majority of BTU's from the water.
So after a couple of winters of use on the upstairs rads,i had a couple of 14 row rads for the main floor to hook up.They each got a run of 1/2 pex.