Cast iron baseboard radiators do not cool off at the same rate within the same apartment

ak3366

Hello, a plumber recently installed 9 cast iron baseboard radiators (9” tall) in the entire apartment, including bathrooms. This replaced copper baseboards. The new cast iron baseboard radiators heat up well when the thermostat turns on, about equally warming up in all rooms. However, once the radiators cool off, only 4 out of 9 keep the heat for a long time while 5 cool off much sooner than others. The ones that cool off sooner are located BOTH on internal and external walls, so my theory about external walls being cooler is out the window. Note that the smallest of the radiators, in the bathrooms, 1.5’ length, stay warm the longest. In the bedroom, one of the 3’ radiators on an internal wall stays warm for a long time while the another 3' radiator in the same room on another internal wall cools off much faster. This particular room may have one radiator much earlier on the supply than the other one, though…Is there a reason why this uneven cooling takes place? I would hope they all have consistent characteristics, given they are all the same brand, OCS Industries. Any ideas would be appreciated. Thank you.

JUGHNE

Are they all on the same floor?

ak3366

Yes the same floor. Actually, correction: they cool off at the same rate, but the issue is that sometimes only 4 out of 9 heat up while the other 5 stay cold when the thermostat turns on. On other occasions, all 9 heat up well. Can this be related to air in the system?

BobC

Is this a single zone system and is there more than one heating loop?

Bob

Jamie Hall

ak3366 said:

Yes the same floor. Actually, correction: they cool off at the same rate, but the issue is that sometimes only 4 out of 9 heat up while the other 5 stay cold when the thermostat turns on. On other occasions, all 9 heat up well. Can this be related to air in the system?

The simple answer is, yes it could be air in the system -- among other things. As @BobC said, though, we need to know more about how this is piped.

ak3366

It's a single zone system. The boiler is on the roof, the apartment is on the top floor, beneath the boiler room. Supposedly, pipes are not run on the same level, but rather go up and down within the walls for each radiator.

JUGHNE

Does each floor have it's own boiler or do you share?

EBEBRATT-Ed

The system most likely needs the air bled out

ak3366

Each apartment has its own boiler. My unit has a dedicated boiler.

GW

Iron is iron, I'd be looking at heat loss issues, greater heat loss will cool off the units faster than rooms with lesser heat loss.

JUGHNE

AK, how well did this work before for your apartment?
What prompted you to change from copper to CI?

I have visions in my mind that because of the boiler on top and radiation under and piping hidden in ceilings and walls, that you get "ghost" flow of hot water migration. If there are tees branching off to various rooms anything could happen with this.
It may have happen before but because of the light weight copper you did not notice.

I wonder if you have a flow check valve at your boiler, these usually are installed in the supply line to keep the water from moving without the pump on which opens the flow check. For your situation you might need a flow check on the supply and also return lines, because the boiler is over your head.

Techman

Ghost flow happens when the boiler is ABOVE the piping?

JUGHNE

I think so. As the water cools in the risers, of which there could be several in this case, the cooler water would drop to the bottom of the system (BB).
Depending upon the piping, the ghost flow areas could be a crap shot.

As I re-read the OP's 2nd comment he could also have "Ghost air" traveling around in the same hidden piping.

I know, a crazy idea, but gravity rules with a change in water density.